Food Microbiology Lecture Notes PDF

Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein Food Microbiology Lec 1: The relationship between food and microorganisms and the new branches of food microbiology One of the most important discoveries in history of biology occurred in 1665 with the help of simple microscope. Antony Van Leeuwenhock discovered the world of m-ms, he discovered the smallest structure units called them: Animalicules. He observed them in the food residues obtained from his teeth, in juice and vinegar and in rain drops. This was the first report about the relationship between food and m-ms. After Leeuwenhock discovery, the scientific community of that time became interested in the origins of the tiny living things until the second half of nineteenth century. Many scientists and philosophers believed that some forms of life could arise spontaneously from non-living matters and they called this process: Spontaneous generation theory (SGT). They believed that snakes and mice could be born from moist soil; flies from manure, maggots (fly larvae), worms, m-ms from spoiled meat and food. In order to refute such theory, Francisco Redi filled two flasks with meat, one left open, the second sealed. Maggots appeared only in open flask after flies entered the flask and laid their eggs, but the sealed flask showed no maggots. However a putrid flavour appeared in the sealed meat as a result of meat putrefaction by anaerobic bacteria (food spoilage process). In order to protect food from microbial spoilage, Spalanzani suggested heating the food extract to kill food m-ms (food preservation process). 2 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein English scientist Tyndall didn’t agree with Spalanzani, because the heat didn’t kill all food m-ms, because the raw food usually contaminated with two groups of m-ms (Food contamination): A) Heat-labile vegetative cells B) Heat-resistant bacterial spores. In order to overcome such problem Tyndall suggested the discontinuous heating (Tyndallization) of food, in which the food heated three successive days every short period of time in order to promote the germination of bacterial spores which resist the heat on first or second day and converted to vegetative cells on third day to be sensitive to the heat. After tyndallization, the European scientists used oil baths, salt solution and steam pressure (autoclave) in order to increase the temperature above water-boiling point to kill heat-resistant bacterial spores (Food sterilization). 1795–Appert discovered food preservation by canning by placing meat in glass bottles and boiled it. In spite of all these experiments, the deep scientific works on food and industrial microbiology was made by the French chemist Louis Pasteur 1857-1887 The main works of Pasteur in this field are: 1- Pasteur demonstrated that m-ms are present in air and can contaminate the food, to prove this Pasteur filled several short-necked flasks with beef extract and then boiled their contents; some were left open for few days. These open flasks were found to be contaminated with microbes. The others sealed after boiling were free of microbes. 2- Pasteur placed the meat broth in flask and bents the neck into S- shape curve (Swan-neck flask) and closed its opening with a cotton plug in the lowest point of neck. The contents of this flask were boiled, the 3 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein meat content didn’t decay even after months, and he concluded that the cotton plug trapped air-born m-ms to protect food from microbial spoilage. 3- Pasteur made a heavy works on food spoilage and on fermentation, he stated that raw food material contain many m-ms causing the spoilage of food product produced from this raw material. He found in the French wine rod-shaped m-ms in addition to the oval-shaped yeast used for production the product. So rod-lactobacilli contaminating the grape produced lactic acid instead of alcohol and spoiled the wine. 4- To kill rod bacteria causing spoilage of wine, Pasteur suggested the Pasteurization of the product. 5- Heavy works on all types of fermentations, Pasteur proposed a (Germ theory of fermentation) He proved that for each fermentation there is a special m-m cause it. 6- Based on the study of butyric-acid fermentation caused by anaerobic Clostridium butyricum, Pasteur made his famous historical statement for first time: Life without oxygen. 7- In addition to his works in food and industrial microbiology, Pasteur strongly proved that: no living things created from non-living matter and the spontaneous generation theory is wrong. Parallel with Pasteurʼs works, other groups of scientists made an emphasis on the role of food m-ms in the food-borne diseases and food poisonings, while third groups focused on the beneficial face of 4 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein food m-ms and used these m-ms as pure bacterial starters to produce improved foods. Storch in 1885 used for first time a pure starter to produce Dannish butter, Feridenreich in 1891 to produce Swiss cheese etc. In the early 1920s, several nasty outbreaks of botulism lead the canning industry to adopt a very conservative heat treatment, known as the 12D process, that reduces the probability of survival of the most heat resistant C. botulinum spores to one in a billion (10-12). At the end of twentieth century a new branches of food microbiology were appeared such as transgenic foods and therapeutic foods. So food microbiology is a multi-purposes science, which has been practiced by human society since the beginning of record history till now in all fields of human activities in medicine, agriculture and industry, so food microbiology at present time includes many old and new branches as shown in the following figure: Therapeutic Foods Transgenic Foods Food Poisonings Food Protection Food Food Hygiene microbiology Dairy Microbiology branches Food-borne diseases Food Biotechnology Definition of Food Microbiology: It is the science studies microorganisms in relation to food from the standpoints of: (1) causing food spoilage (deterioration), (2) causing foodborne diseases (infection or poisoning) and (3) those has beneficial use in food processing (like baker’s yeast and probiotic microorganisms). 5 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein Food microbiology Lec2: Microbial Contamination of Food The raw food usually produced, contaminated with microorganisms (m- ms), because the plants and animals from which the raw food is produced grow in natural environments in contact with soil, water rich in m-ms in addition to the microbial flora of plant and animal from which produced, which are considered as: natural sources of food contamination. Foods also get heavy contamination during handling and processing. I- Natural Sources of Food Contamination: 1- The Water: The water is in continuous contact with foods from the field or farm of production to the table of food in the restaurants and houses (FFTT) as a: a) Irrigation Water b) Cleaning Water c) Processing Water d) Cooling Water. Irrigation water is highly loaded with m-ms because it is raw water rich in organic matter; moreover in the field this water gains more organic residues from plant, sewage, manure, soil, so this water in shallow field streams converted to the optimum medium for microbial growth. This water contaminates the raw food with two groups of m- ms: A)) Psychrophilic normal bacterial flora of water, which will be responsible for food spoilage during refrigeration. B)) Mesophilic contaminating flora which reached the water from soil, sewage, animals, humans, etc. which will be responsible for food- borne diseases and poisonings. Cleaning process and cooling water if they are not disinfected also contributed in the food contamination. 6 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein 2- The Soil, Manure and Sewage: The soil is rich in microbial spores and continuously contaminate the raw food with bacterial and fungal spores, particularly heat-resistant spores that resist the heat treatment of food. Sewage and animal manure used as fertilizers contaminate the food with very dangerous bacteria, viruses and parasites. 3- The animals and plants: The plants particularly leafy vegetables loaded with m-ms because in contact with sources of contamination such as: soil, sewage, water, manure, rodents etc. These m-ms reach the food produced from raw plants. Animals carry many m-ms causing the dangerous diseases to the human such as brucellosis, tuberculosis, anthrax etc. the food gains the m-ms through meat, milk, eggs etc. Generally the animal origin foods more dangerous than plant origin foods because: a) There are hundreds microbial diseases associated between animal and humans, so these microbes transferred to the human through food. b) Microbial spoilage of animal origin food leads to production chemical compounds toxic to human such as toxic polypeptides, fatty acids, ketones, aldehydes etc. 4- The air: The air of open production field usually poor in m-ms and not suitable for growth of m-ms because: 1) Poor in organic matter. 2) Low moisture because of the sun heat. 3) Bactericidal effect of sun U. V. light. 4) Continuously removing of m-ms by winds current. 7 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein However the air of closed food plants, restaurants, food stores; loaded with m-ms and may be served as a source of contamination of food and prepared meals. In such case it is necessary to disinfect the air of closed buildings by bactericidal chemicals or bactericidal U.V. lamps and using special cooling-system and other sanitary particles (replace the oxygen by nitrogen in food stores). II- The food contamination during handling and processing In addition to the natural sources of contamination, the food expose to the heavy contamination during a long way from the field of production to the table of eating (FFTT) through the following stages: 1- Harvesting or collection of raw foods in the farms. The raw food may be contaminated from the soil of the field, manures, insects, rodents, birds, collectors, boxes, equipments etc. 2- Transportation. The food contaminates from the boxes, bags, truck, cars particularly from permanent societies of contamination which formed from food-residues in the boxes, containers or cars. Also the raw food may be contaminated with toxic chemicals if the same car; container used for transportation of fertilizers, pesticides, fuel etc. 3- Manufacturing in the food plants 4- Marketing and Distribution The most important stage of these four stages is the stage of food processing in the food plant for this reason a strict constructions and rules of food plant sanitation was issued for long time. 8 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein Food Plant Sanitation Food exposed to all sources of contamination in the food plant: air, water, soil, sewage, rodents, insects, food handlers, surfaces, equipments, containers, etc. so plant manager hold a big responsibility for production a food with following characteristics: 1) Clean food 2) Fresh food 3) Pure food 4) Safe food 5) Food with normal character 6) Food with high nutritive value. In order to achieve these goals, there are many quality control section established in each plant: 1 Pest control section 2 Chemicals control section 3 Cleaning and Sanitizing control section 4 Microbiological control section 5 Food handlers, employees, workers health section Microbiology – Quality control in food plant Microbiological section of quality control responsible for microbiological examinations of the following items: I) Sites and materials of food plant 1- Microbiology of processing water and drinking water In addition to pathogenic m-ms it is necessary to examine the iron and manganese bacteria, slime producing bacteria and other undesirable bacteria. Chemical composition also needed particularly the hardness of water, iron & manganese content and excessive organic matter. 2) Microbiology of products: Raw materials, ingredients, additives, end product, packaging materials, etc. 9 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein 3) Microbiology of sewage and waste-treatment units. 4) Microbiology of food plant and equipments: Floor, ceiling, walls, windows, doors, sinks, air, processing surfaces and equipments …etc. 5) Microbiology of food stores, cartons, bags, containers, cars, trucks …etc. II) Microbiological examinations of food handlers, workers, employees. Food handlers are very dangerous source of food contamination especially in our country; because they are closely contact with the food from the field of production to the fork of consumer (FFF). They contaminate the food by their dirty hand, acne on the face mostly contaminate food & prepared meals with two groups of pathogenic m-ms: 1- Respiratory system pathogens through sneezing, coughing, laughing, chatting; by droplets. 2- Enteric pathogenic m-ms. Due to improper hygiene habits. For these reasons a special care must be taken with the food handlers from the health point of view. So they must wear a special head cover, mask, gloves, work coat, shoes.. etc. Food handlers' external feature must be similar to the heart surgeon, moreover food handler is more dangerous than surgeon; because if he contaminates the food, hundreds consumers may be killed, while the surgeon may kill only one person (patient) in such case. The main microbiological tests in food plant The tests are determined according to the food type from this list of tests: 1) TBC : Total Bacterial Count 2) TYMC: Total Yeast Mold Count 3) TPBC: Total Psychrophilic Bacterial Count 01 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein 4) TTBC: Total Thermophilic Bacterial Count 5) TSC : Total Spore Count 6) TCC: Total Coliform Count and Fecal E. coli 7) Enterococci 8) Clostridium perfringens 9) Test for Pathogenic Bacteria 10) Test for Parasites 11) Test for Viruses 12) Test for Bacterial Toxins 13) Test for Mycotoxins Food Adulteration The famous world-wide organization Food and Drug Administration (FDA) considered the food product in food plants as (Adultered food) in the one of the following cases: 1) If the food contains: Filthy, Putrid, or decomposed substances. 2) If the food contains: Poisonous or unsafe chemicals & food additives 3) If food has been prepared, handled or packed under unsanitary conditions whereby become contaminated with m-ms. and chemicals. 4) If food is a product of diseased animal or an animal was died not by slaughtering. 5) If food container is composed of poisonous substances. 00 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein Food microbiology Lec3 : Microbial Spoilage of Food Microbial spoilage is any organoleptic change in food makes it unacceptable by consumer. The change usually occurred in the flavor, color, odor, taste and texture. In spite, the differences between the signs of spoilage according to the type of food, there are three main signs of microbial spoilage are common in most foods: I) Color change: Many colors may be appeared on the surface of the spoiled food as a diffusible exopigments or colored colonies with endopigments. This food discoloration caused by bacteria, yeasts and molds. 1- Bacterial Discoloration Appeared Color Causative agents Fluorescent yellow-green Pseudomonas fluorescence (pyoverdin production) Blue P. aeruginosa (pyocyanin production) Black Bacillus sp. (Melanin production) Yellow Micrococcus luteus , Flavobacterium Rose Micrococcus roseus Red Serratia marcescence 2) Yeast Discoloration A) White-Pale colonies of non-pigmented yeasts ex. Saccharomyces cerevisiae. B) Red-Pink colonies of pigmented yeasts ex. Rhodotorula. 02 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein 3) Mold Discoloration Wide range of water-soluble and insoluble pigments and color mold colonies on food surfaces. II) Sliminess: Activity of m-ms in the food may be lead to form a slime on the food surface by one of the following mechanisms: 1) Production of light slime; by pectolytic bacteria such as Erwinia carotovora which lyses the pectin in plant tissues (Pectin is adhesive material between plant cells). 2) Production of heavy viscous slime; through production of viscous polysaccharides such as levan and dextran from food mono and disaccharides by Pseudomonas viscosa or Leuconostoc mesenteriodes. III) Changes in flavours and odors: The normal acceptable flavor of food may be changed to non- acceptable flavor in spoiled food; the change is occurred by two mechanisms: 1- Microbial destruction of natural flavor compounds of food; as in the destruction of natural flavor of butter di-acetyl to off-flavor acetyl-methyl carbinol by Pseudomonas fragi, or destruction of natural fruit organic acid to unacceptable alcohol, ethers, ketones, aldehydes. 2- Microbial production of unacceptable off-flavors and off-odor in the food as in the following examples: 03 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein Bacterial production of off-flavor or off-odor in food Off-flavor Causing m-ms Mechanisms of production Souring flavor Lactobacillus Foods sugar Lactic acid Acetobacter, Acetic acid Probionibacterium, Probionic acid Clostridium butyricum Butyric acid Bitterness flavor Pseudomonas Protein hydrolysis, Fatty acid Bacillus degradation, sugar Bitter Aldonic acid Sulfide odor Clostridium Proteus Protein Sulfur A.A. H2S Rancidity Lipolytic m-ms Lipid Fatty acids Ketones Unclean flavor Escherichia coli (heavy Tryptophane Skatol+Indol growth) Earthiness (soil Streptomyces Production of "Geosmin" flavor) adsorbed by food contaminated with soil Cabbage & potato Pseudomonas Production of vegetable, fruit flavor flavour in refrigerated milk & meat Soapiness of meat and Pseudomonas Reaction between free A.A. and cheese free F.A. leads to production of soapiness compounds F. A. Fatty acid A. A. Amino acid m-ms microorganisms 04 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein Indicator Bacteria of Food Contamination & Microbiological Standards of Food We should examine the food and food plants for contamination indicators for the following purposes: 1) To detect the food is healthy or not healthy for human consumption. 2) For assessment the sanitary practices of food plant. 3) The official standards are meeting the produced food. (For compatibility with official standards and sanitary constructions). Routine tests for selected food pathogens or toxins such as salmonella or staphylococcal enterotoxins are necessary whenever epidemiological outbreaks are occurred. 1) In most cases such as infectious hepatitis, detecting methods for causative agent are not available to food microbiologists. 2) For other food-borne infections such as shigellosis, the methods may be unreliable, especially when the pathogens are distributed in food heavily contaminated with other m-ms. 3) In addition tests for pathogens directly are very dangerous for laboratory workers. For all these reasons and difficulties all microbiological labs firstly test species which are more readily cultivated, enumerated, not dangerous to the workers and environment, normal inhabitants of human and animal intestine which indicate the exposure of food to wastes and conditions containing pathogenic m-ms and their toxic products. These species so used are called (Indicator Bacteria). 05 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein Such indicators also help in assessing the quality of food and the presence of dirty particles such as insects parts, hairs, rodents excretion.. etc. Microbiological Standards of Food The main purposes of microbiological standards of food are to give assurance that: 1) The food will be acceptable from the public health standpoint. 2) The food will be acceptable from the nutritive value and normal characteristics. 3) The food will be acceptable from an esthetic viewpoint. (Not filthy with fecal materials, parts of vermin, pus cells, mycelia…) 4) The food will have keeping quality that should be expected. In order to issue food microbiological standards it is important to take into consideration the following principles. (1,2,3,4 example1) (5example2). 1- Determination the higher limit of m-ms permissed in each food. 2- Determination the types and higher limit for each type of m-ms in each food. 3- All types of food must be free of any pathogenic and toxigenic m- ms (in some cases except staphylococci). 4- For the same food may be more than one standard according to the state of food (Fresh, canned, minced, dried, frozen..etc.). 5- In some cases as in the milk, the food divided into many grades: A, B, C) according to the microbial content, and a standard for each grade. 6- The standards may be not identical for all countries, all town; because different conditions between these countries as follow: A- Level of food productivity and available foods. 06 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein B- Economical situation C- Sanitary situation D- Nutrition habits E- Emergencies outbreaks such as war and catastrophes. There are many organizations responsible for microbiological standards of foods such as: 1) WHO: World Health Organization - U. N. 2) FAO : Food Agriculture Organization - U. N. 3) CAC : Codex Alimentaricus commission 4) FDA : Food & Drug Administration 5) APHA: American Public Health Association 6) EPA : Environmental Protection Agency 7) EOF : European Organization of Food 8) COSQC: Central Organization for Standardization and Quality Control. (Local organization). Examples of Microbiological Standards of Food 1) Bacteriological Standards of meat, chicken, fish (principal 1,2,3,4) Type and state of meat m-ms Maximum count/gram Fresh red meat T.B.C. 1-5x106 E. coli 10-50 Salmonella ___ Minced red meat T.B.C. 1-5x107 E. coli 50-100 Salmonella ___ Frozen red meat T.B.C. 1-5x106 E. coli 10-50 Salmonella ___ Fresh frozen chicken T.B.C. 1x105 E. coli 10-50 Salmonella ___ 07 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein 2) Milk and milk products m-ms Milk Grades Milk powder (m- Grade A Grade B Grade C count) Raw Pasteurized Raw Pasteurized Raw& Standard Extra Pasteurized quality T.B.C 2x105 3x104 1x106 5x104 More than 1x105 5x104 Coliform 10 10 10 10 count of B. 90 90 grade 3) Butter Tests Microbial count T.B.C 1x104 Mold & Yeast 20 Psychrophilic Bacteria 103 Lipolytic Bacteria 103 Proteolytic Bacteria 50 Coliforms 10 Fecal sterptococci 10 4) Ice cream Tests Microbial count T.B.C 1x104 Coliforms 10 S. aureus 10 Salmonella ___ 08 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein Food microbiology Lec 4: Intrinsic & Extrinsic Factors Affecting Microbial Spoilage of Food There are many factors related to the food itself (Intrinsic) and factors surrounding the food (Extrinsic) strongly affect the type and time of food spoilage, some of these factors are: I- The number and kind m-ms in food Generally when the number of m-ms on food surface is high; the spoilage will be occurred faster and vice versa, for example slime appeared on the meat surface with high load faster than on the meat with low number of bacteria. This is not always true, because in spite of a high number of m-ms there is no microbial group or type which can act on a food with a special chemical composition as in the proteolytic group in protein food and the lipolytic group in fatty food. 4 3.5 3 *High microbial load 2.5 log No. of Bacteria 2 1.5 1 0.5 *low microbial load 0 0 0.5 1 1.5 2 2.5 3 3.5 Days of Slime Appearance on meat surface II- Chemical composition of food M-ms need simple sources of carbon, nitrogen and energy for growth and activity, so food with simple chemical composition and simple 09 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein sources of carbon such as glucose and nitrogen as amino acids spoiled faster than complex food. According to the main chemical constituent, the foods are divided into three big groups: 1- Protein Foods: The main spoilage in this food is: Putrefaction which occurred as follows: Protein food True proteolytic m.o Polypeptides Proteolytic m.o Amino acids Organic acid, Amines, Gases, Putrid compounds The main pathways of amino acid break down which lead to putrid compounds production: A. Deamination CH3CHNH2COOH Alanine deaminase CH3COCOOH+NH3 B. Decarboxylation CH3CHNH2COOH Alanine decarboxylase CH3CH2NH2+CO2 Escherichia coli C. Tryptophan Skatole + Indole 2- Sugar Foods The common spoilage is fermentation. The type of fermentation is determined according to the sugar content: 21 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein 1- Low sugar food (Meat) Bacterial oxidation Organic acid+ Gases 2- Medium sugar food (Milk)Organic acid fermentation Lactic A+Org.A.+Gases 3- High sugar food (Juice) Alcoholic fermentation by yeast Alcohols very slow alcoholic fermentation 4- Very high sugar food (Honey) Little amount by osmophilic yeast of Alcohol (Yeasty honey) 3- Fatty Foods The main spoilage is: Rancidity; there are two main types of rancidity: 1) Oxidative Chemical Rancidity: All fats are exposed this non-microbial rancidity during the storage particularly in the light and sun. This rancidity occurred as a result of autochemical reaction in the fat and produce rancid fatty acids, ketones and aldehydes. 2) Microbial Hydrolytic Rancidity: Occurred by the activity of lipolytic m-ms. Lipid lipase by lipolytic m.o Fatty acids+ Glycerol Rancid aldehydes& Ketones III- Food pH: Most foods are with neutral pH suitable to activity of most of bacteria and spoiled faster than some foods with low or high pH. Food pH strongly affects the type of m-ms growing in that food and consequently the type of spoilage as shown in the following table: 20 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein Table: The relationship between food pH and food spoilage Food Type Food pH Main Spoilage m-ms Alkaline Foods 8-10 Alkaliphilic m-ms, some strains Egg white (pH 9.6) of Pseudomonas and Proteus Neutral Foods 6-7 Most of Bacteria Low acid Foods 5-6 Acidophilic bacteria, Fruits&Vegetables Lactobacillus Medium acid Foods 4-5 Most yeasts, Lactobacillus Fruit Juices& Fermented milk Acid Foods 3-4 Acetobacter, Lactobacillus Juices& Pickles High acid Foods 2-3 Rarely spoiled by m-ms Lemon Juice (pH 2) *If occurred by fungi IV- Food Moisture: Water is necessary to the growth of bacteria and to the enzymatic activity in the food, particularly the food free water which could be expressed as Water activity aw (aw=P1/P2) P1: vapor pressure of solution, P2: vapor pressure of solvent (usually in food is water). Food with aw more than 0.90 is spoiled by bacteria while less than 0.90 spoiled by mold and yeasts, except some rare cases: M-ms causing spoilage Lowest aw Value Examples Bacteria 0.91 Fresh meat, Fresh cheese Yeasts 0.88 Salted meat, Salted cheese Molds 0.80 Dry fruits, Grains Halophilic Bacteria 0.75 Salted foods Xerophilic Molds 0.65 Dry fruits, Grains Osmophilic Yeasts 0.60 Sugar Foods (Jams, Honey) No Microbial Spoilage ˂0.50 Corn flaks, Milk powder 22 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein V- Other factors less important such as: 1- Aerobic & anaerobic conditions. 2- Biological structure of food particularly the surface of food which protects the entrance of m-ms inside the food. 3- The presence of antimicrobial substances in the food. 4- Some food treatments that stimulate the microbial growth, for example: A- Washing with raw water without drying or disinfectants. B- Non-efficient heating that promotes the spore germination, not killing them. C- Mincing or slicing the food: such treatment lead to promote the microbial growth in the minced food because: 1) Increasing the food surfaces for microbial growth. 2) Increasing the oxygen content inside of food. 3) Outflow the food juices rich in nutrient from the inner tissues to form optimal medium for microbial growth. 4) Increasing the sources of contamination from mincing and slicing machines; rest food in these machines forms permanent sources of contamination, knife working surfaces, etc.. Investigation and inspection of food disease outbreaks Gastro-intestinal disturbance resulting from the ingestion of food (Food illness) have a variety of causes: 1- Overeating 2- Allergies 3- Nutritional Deficiencies 4-Toxic Plants 5- Toxic Animals 6- Toxic Chemicals 7- Bacterial Intoxication 8- Bacterial Infection 9- Food Mycotoxins 10- Fungal Infections 11- Food Viruses 12- Food Parasites 13- Unknown Causes. 23 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein However for long time, thousands researches proved that m-ms are the main cause of food illness. For example the following table has been issued by U.S. disease center: Disease agent Percentage % A- Microbial agents 65 1- Staphylococcus aureus 25 2- Clostridium perfringens 15 3- Clostridium botulinum 6 4- Salmonella 10 5- Other Bacteria 3 6- Viruses& Parasites 6 B- Chemicals & Unknown 35 The most important food microbial diseases are: food microbial disease Causative agent Staphylococcal Food Poisoning Staphylococcus aureus (SFP) Botulism Clostridium botulinum Clostridium perfringens F. P. Clostridium perfringens Salmonellosis Salmonella sp. A- Typhoid fever (human) B- Paratyphoid fever(zoonotic) Shigellosis, Bacillary dysenteriae Shigella sp. Food poisoning Enterotoxigenic E. coli Enterocolitis Yersinia enterocolitica Food poisoning Vibrio parahaemolyticus Food poisoning Bacillus cereus Food poisoning Entamoeba histolytica, Cryptosporidium, Giardia Chemicals, toxic plants, toxic Arsenic , Vicia faba , Shark animals 24 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein The main purposes of the investigation of an outbreak of food born disease are to determine: 1- How the foodstuff became contaminated? 2- How the growth of toxigenic or infectious m-ms could take place. 3- How can we prevent the repetition of this case? This requires: 1) Location of the outbreak 2) Identification of the causative agents 3) Route of transmission 4) Demonstration of the opportunity for growth of pathogen 5) Proof that pathogen has infected the publicity given an outbreak. The investigation team includes: 1- Field group: A- Persons consumed suspected food, physicians and nurses who are treating the victims. B- Collecting samples of suspected food, specimens from food handlers and patients and transmitting them to lab. C- Inspects the site where the food was stored, prepared, served and sold. 2- Lab. group: Microbiological and chemical tests. 3- The person in charge who can explain the data from all sources to determine the cause and the source of disease outbreak. Collection the Food Inspection 1- Collection of food samples 2- Collection of specimens from human sources a- Fecal samples b- Blood samples c- Vomit 3- Laboratory testing: 25 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein A- Test for botulism B- Test for Staphylococcal food poisoning C- Test for Salmonella and Shigella D- Test for C. perfringens & B. cereus E- Test for Mycotoxins F- Test for Parasites: Entamoeba histolytica, Cryptosporidium, Giardia lamblia G- Test for viruses H- Test for toxic plants & animals I- Test for pesticides and heavy metals. The practices employed to protect food from dangerous m-ms: 1- Keep food free from contamination with pathogens and food handlers and other sources. 2- Prevention the microbial growth in food 3- Rejection suspected food 4- Educate the public about the prevention of food borne illness. 26 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein Food-borne Diseases Lec 5: Food-borne Infections and Intoxications Food-borne Diseases: Gastrointestinal disturbances resulting from the ingestion of food have a variety of causes, e.g. overeating, allergies and nutritional deficiencies; actual poisoning by chemicals, toxic plants or animals; toxins produced by bacteria; infestation by animal parasites and infection by microorganisms. Fig (1): Groups of Foodborne Pathogenes Pathogenic Bacteria Gram‐positive bacteria Gram‐negative bacteria Clostridium perfringens. cillus cereus and other Bacillus spp... Mycobacterium bovis. Parasitic Protozoa and Worms non‐O1 and non‐O139. nensis... Francisella tularensis Pathogenic Escherichia coli Group. c Escherichia coli (ETEC). gastrointestinal illness (EHEC) Ascaris lumbricoides and Trichuris trichiura 27 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein Viruses ASP, AZP) otoxin Other Pathogenic Agents Encephalopathies Natural Toxins FBD is an acute illnesses associated with the recent consumption of food. These illnesses often are grouped together because they may have similar symptoms. Ordinarily the term "Food Poisoning" as applied to diseases caused by microorganisms, is used very loosely to include both illnesses caused by ingestion of toxins elaborated by the organisms & those resulting from infection of the host through the intestinal tract. A further classification food borne diseases is shown in Fig. (2), here all food borne diseases are subdivided into poisoning and infections. Food poisonings can be the result of either chemical poisoning or the ingestion of toxicant (intoxication). The toxicant might be formed naturally in certain plants or animals or be a toxic metabolic products excreted by a microorganisms. Bacterial food intoxication refers to foodborne illnesses caused by the presence of bacterial toxin Preformed in the food. Bacterial food infection refers to foodborne illnesses caused by the entrance of bacteria into the body through ingestion of contaminated foods and reaction of body to their presence or their metabolites. 28 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein Food borne infections Food borne intoxications Entrance of pathogenic microorganisms Presence of bacterial toxin Preformed in contaminating food into the body, and the food. the reaction of the body tissues to their presence. long incubation periods short incubation periods (minutes to hours) usually characterized by fever characterized by lack of fever. These can either be fungal, bacterial, Food borne intoxications can be viral or parasitic classified into: a. Bacterial food borne inf. a. Bacterial intoxications b. Mycotic food borne inf. b. Fungal intoxications c. Viral food borne inf. c. Chemical intoxication d. Plant toxicants, and e. Poisonous animals. 29 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein 1- Botulism: Caused by the presence of toxin produced by Clostridium botulinum in food. 2- Staphylococcal intoxication: Caused by a toxin produced by Staphylococcus aureus in food. Food infections also can be divided into two types: 1) Those in which the food does not ordinarily support the growth of the pathogens but merely carries them, pathogens such as those causing tuberculosis, diphtheria, dysentery, typhoid fever, brucellosis, cholera, infectious hepatitis, Q-fever, etc... 2) Those in which the food can serve as culture media for growth of pathogens to numbers that will increase the likelihood of infection of the food consumers; those include Salmonella spp., Vibrio parahaemolyticus and enteropathogenic Escherichia coli. Outbreaks of food infections of the second type are likely to be more explosive than outbreaks caused by other intestinal pathogens. Staphylococcal Food Poisoning (SFP) Staphylococcal Food Poisoning is an intoxication caused by the ingestion of an enterotoxin formed in food during growth of certain strains of Staphylococcus aureus. The toxin is termed as enterotoxin because it causes gastroenteritis of inflammation of the lining of the intestinal tract. Most enterotoxin producing S. aureus cultures are coagulase-Positive (CoPS), produce a thermo-stable nuclease, however not all CoPS are necessarily enterotoxigenic. Some of the toxigenic cocci are very salt- tolerant (10-20% NaCl), they also are fairly tolerant to dissolved sugars (50-60% sucrose). 31 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein At least 10 of the coagulase-Negative Staphylococcus spp. (CoNS) produce enterotoxins, for example: S. epidermidis & S. haemolyticus. Incidence in food According to the Centers for Disease Control and Prevention (CDC), S. aureus is a common bacterium found in the nose and on the skin of about 25 percent of healthy people and animals, so it is expected to exist; at least in low numbers in any or all food products that are of animal origin, or in those that are handled directly by humans, unless heat processing steps are applied to affect their destruction (milk and milk products including pasteurized milk, yoghurt, chocolate milk, fermented milk, cream filled pastries, poultry, fish, shellfish, meat and meat products, non meat salads, egg and egg products, vegetables and cereal products have been involved). Temperature growth range o In general growth occurs in range 7-47 C and enterotoxins are produced between 10 oC& 46 oC with the optimum between 40 oC & 45 oC. These minimum and maximum temperatures for growth and toxin production assume optimal conditions stable to the other parameters. Effect of salts Although S. aureus grows well in culture media without NaCl, it can grow well in 7-10% conc. of NaCl and some strains can grow in 20%. The maximum conc. that permit growth depends on other parameters such as temp., pH & aw. Effect of pH & water activity (aw) Regarding pH, S. aureus can grow over the range 4-9.8 but its optimum is the range 6-7. With respect to aw the staphylococci are unique in being able to grow at values lower than any other non halophilic bacteria. 30 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein Growth has been demonstrated as low as 0.83 under otherwise ideal conditions, although 0.86 is the generally recognized minimum aw. Symptoms of SFP include diarrhea, vomiting, and abdominal pain. They are usually not life threatening. Symptoms may appear rapidly, sometimes in as little as 30 minutes. However, it typically takes up to six hours for symptoms to manifest. Most cases of SFP do not require treatment because the disease will pass on its own. Most people get over the food poisoning in about two days. According to the U.S. Food and Drug Administration (FDA), SFP related deaths are very rare. However, there is increased risk for this complication among the elderly, small children, and people with weakened immune systems (Immunocompromized). The minimum quantity of an enterotoxin needed to cause illness in humans is about 20 ng. The repertoire of S. aureus SEs/SEls comprised 22 members, excluding molecular variants: (i) the classical SEA, SEB, SEC (with the SEC1, SEC2 and SEC3, SEC ovine and SEC bovine variants), SED and SEE, which were discovered in studies of S. aureus strains involved in SFP outbreaks, and classified in distinct serological types ; and (ii) the new types of SEs (SEG, SEH, SEI, SER, SES, SET) and SEls (SElJ, SElK, SElL, SElM, SElN, SElO, SElP, SElQ, SElU, SElU2, and SElV). The toxic shock staphylococcal toxin (TSST-1), initially designated as SEF, lacks emetic activity These SE are proteins have a remarkable ability to resist heat and acid, therefore, they may not be completely denatured by mild cooking of contaminated food, SE ability to induce emesis and gastroenteritis, they are resistant to inactivation by gastrointestinal proteases including pepsin, trypsin, rennin and papain, thus they can easily outlast the bacteria that produce them. 32 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein Botulism Botulism is an intoxication caused by ingestion of food containing the neurotoxin (botulinum toxin), which is produced by Clostridium botulinum, a Gram positive, anaerobic, spore forming rod with oval to cylindrical terminal spores. Seven antigenically distinct toxin types (A, B, C, D, E, F, G) have been identified. Types A, B, E, and F cause natural disease in humans. The vast majority of disease is caused by types A, B, and E; type F rarely occurs, Types C and D cause natural disease in birds, horses, and cattle. The species is further subdivided on the basis of proteolytic activity: the main strains of concern in foods are proteolytic types A, B, F and G, and non proteolytic type E as are some strains B and F. Growth & Toxin production Toxin production by Clostridium botulinum depends on the ability of the cells to grow in a food and autolyze there, for the types A, B, E&F toxins apparently are synthesized as large, comparatively in-active proteins which become fully toxic after some hydrolysis. Therefore the factors that influence spore germination, growth and hence toxic production are of special interest. These factors include the composition of the food especially its nutritive properties, moisture, pH, salt content, temperature and time of food storage. The concentration of sodium chloride necessary to prevent growth & toxin production in food depend on the composition of the food and the temperature. A pH near neutrality favors C. botulinum, the minimal pH at which growth and toxin production will take place depends on the kind of food & the temp. A pH of 4.5 or lower will prevent toxin production in most foods. 33 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein The optimal temp. for toxin production & growth of the proteolytic strains is about 35˚C while 26-28˚C is usually given for the optimal temp. for the non proteoytic strains. Botulinum toxin is a protein, is so powerful that only a tiny amount is sufficient to cause death. It is absorbed mostly in the small intestine & paralyzes the involuntary muscles of the body. An important characteristic is its comparative thermolability. The heat treatment necessary to destroy it depends on the type of the organism producing the toxin & the medium in which it is heated. Salmonellosis Salmonellosis is a foodborne infection caused by Salmonella bacteria. Most people infected with Salmonella develop diarrhea, fever, vomiting, and abdominal cramps 12 to 72 hours after infection. In most cases, the illness lasts four to seven days, and most people recover without treatment. In some cases, the diarrhea may be so severe that the patient becomes dangerously dehydrated and must be hospitalized. Incriminated food: Poultry, pork, beef and fish (seafood), if the meat is prepared incorrectly or is infected with the bacteria after preparation. Infected eggs, egg products, and milk when not prepared, handled, or refrigerated properly tainted fruits and vegetables. Carriers: Humans and, occasionally, domestic animals are the carriers of Paratyphoid Fever. Members of the same family can be transient or permanent carriers. Conditions necessary for an outbreak The following conditions are necessary for an outbreak of foodborne Salmonella gastrointestinal infection: 34 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein 1- The food must contain or become contaminated with Salmonella bacteria 2- These bacteria must be there in considerable numbers, either because of contamination with Salmonella or more often because of growth; these high numbers mean that the food must be a good culture medium, the temp. must be favorable and enough time must be allowed for appreciable growth. 3- The viable organisms must be ingested S. enteritidis and S. typhimurium are the most common, the incubation period for S. enteritidis is typically between 6&48 hours. Prevention of outbreak 1- Avoidance of contamination of the food with Salmonellae from sources such as diseased human beings & animals & carriers. e.g.: contaminated egg. 2-Destruction of the organisms in foods by heat (or other means) 3- Prevention of the growth of Salmonella in foods by adequate refrigeration or by other means. #Typhoid fever occurs when Salmonella bacteria enter the lymphatic system and cause a systemic form of salmonellosis. Endotoxins first act on the vascular and nervous apparatus, resulting in increased permeability and decreased tone of the vessels, upset thermal regulation, vomiting and diarrhea. Septic shock may also develop. Paratyphoid fever is an enteric illness caused by one of the following three serotypes of Salmonella enterica subspecies: S. Paratyphi A, S. Paratyphi B and S. Paratyphi C. Like S. Typhi they are transmitted by means of contaminated water or food. The paratyphoid fever bears similarities with typhoid fever, and the two are referred to by the common name enteric fever. The course of paratyphoid is more benign. 35 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein Bacillus cereus food borne illness This is a food borne illness caused by consumption of enterotoxins produced by some strains of Bacillus cereus. The organism produces the following enterotoxins which are involved in a food borne intoxication A- Two diarrhoeal enterotoxins: -hemolysin BL enterotoxin, non- hemolytic enterotoxin, and B- Emetic toxin Incriminated foods: meat, eggs and dairy products, Cereal dishes e.g. rice, spice, mashed potatoes, herbs, vegetables, minced meat, cream and milk pudding have been involved in B. cereus poisoning. Symptoms of disease in man Emetic syndrome The syndrome is characterized by nausea, vomiting, abdominal cramps and sometimes diarrhea that occurs 1-6 hr after consumption of contaminated food. The syndrome is associated with ingestion of rice and pasta based foods. Diarrhoea syndrome In the diarrhea syndrome, patients experience profuse diarrhoea (watery stool), abdominal cramps and tenesmus (rarely vomiting) beginning 8 to 16 hours after ingestion of contaminated food. Fever is absent and symptoms resolve within approximately 12 hours. 36 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein Clostridium perfringens intoxication This is a food borne intoxication caused by Clostridium perfringens enterotoxin (CPE) produced in the gastrointestinal tract by enterotoxigenic strains of C. perfringens. The organism is found in the soil, dust, water, sewage marine sediments, decaying materials, intestinal tracts of humans and other animals. This organism is a spore-forming, anaerobic, gram positive bacillus. Food poisoning strains have a variety of origins including human and animal feces, abattoirs, sewage and flies. Spores produced by these organisms can resist boiling for 4 or more hours. If the spores are present as contaminants on raw meat they may resist boiling or steaming, and on slow cooling the spores will germinate into rapidly multiplying bacterial cells, which produce large amounts of toxin. Clostridium food borne intoxication is caused by the ingestion of food containing large numbers of vegetative cells of enterotoxigenic C. perfringens type A and some type C and D strains. These cells multiply in the intestine and sporulate releasing Clostridium perfringens enterotoxin (CPE). Sometimes CPE may be pre-formed in food, and once the food is consumed, symptoms may occur within 1-2 hours. Clostridium perfringens enterotoxin (CPE) is synthesized during sporulation. CPE is heat labile (destroyed at 60oC for 10 min) and its activity is enhanced by trypsin. 37 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein Note: The food poisoning strains are heat resistant and survive heating at 100oC for 1 hr). Incriminated food: The food involved are those that are prepared one day and served the next day. Foods that have been involved include red meats, chickens, fish, pork, fruits, vegetables, spices etc. The heating of such foods is inadequate to destroy heat resistant endospores, Upon cooling and warming the endospores germinate and grow. Cooking kills the vegetables cells of Cl. perfringens but activates surviving spores, which will germinate and multiply. Foods poisoning occurs when the level reaches 107-108 cells/g of food, Growth is enhanced by anaerobic conditions achieved after removal of oxygen by cooking Symptoms of Diseases: Symptoms appear 6-24 hours after ingestion of a large number of viable vegetative cells up to 5x108/g food, but not after ingestion of spores. Symptoms include nausea, intestinal cramps, pronounced diarrhea, vomiting is rare and the illness takes a duration of 1-2 days. 38 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein Important informations about FBD According to health risk the food could be divided into two groups: 1- High-risk foods: are those foods that are most likely to be the vehicles of the food-poisoning and disease-causing pathogens under favorable conditions support the multiplication of pathogenic bacteria such as: A) All cooked meat, poultry, fish, eggs and their products. B) All foods which do not exposed to food treatments. C) Ready to eat foods (fast foods). 2- Low-risk foods: such as preserved foods (Sterilization, canning, drying etc.), acid foods such as vinegar, high acid juices pH˂ 4. Foods with high sugar, salt, fat content. Generally the most common diseases caused by contaminated food are shown in the following table: Disease Contaminated Food Microbial agent Tuberculosis Milk Mycobacterium tuberculosis Anthrax Meat Bacillus anthracis Brucellosis cheese Brucella melitensis Staphylococcal Food Bakary products Staphylococcus aureus Poisoning Salmonellosis Food Poisoning Poultry, eggs Salmonella spp. Botulism Food Poisoning Canned foods Clostridium botulinum Fungal Food Poisoning Cereals, nuts Aspergillus flavus (Aflatoxin) Parasites diseases Meat, leafy vegetables Parasites, Protozoa, Worms Viral diseases Milk, vegetables Hepatitis, Poliomyelitis viruses Toxic plants, animals, toxic Meals prepared from toxic Non-Microbial agents chemicals (Non-microbial plants, animals, food diseases) contaminated with chemicals Foodstuffs may become contaminated with viruses by two ways: 1) Primary Contamination: some human viruses have been found in animals which then products of this animal may act as a vehicle for transmission to the human. 2) Secondary Contamination: This occurs after the time of slaughtering or harvesting. The main source of secondary contamination is via food handlers during food preparation or processing. 39 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein Lec 6: Listeriosis Listeriosis caused by Listeria monocytogenes which is a Gram- positive rod, non-spore-forming,motile with peritrichous flagella , facultatively anaerobic, grows at 0-45 °C (psychrotrophic). The bacteria are able to grow in the presence of 10% salt. Listeria monocytogenes is a special problem since it can survive adverse conditions. It is salt tolerant surviving concentrations as high as 30% for 100 days at 39.2 ºF. Listeria is now recognized as an important food borne pathogen. Symptoms: host Influenza-like symptoms such as fever, headache and occasionally gastrointestinal symptoms or symptoms may be so mild that they go unnoticed. Listeriosis in humans is not characterized as a unique set of symptoms because the course of the disease depends on the state of the host. Non-pregnant healthy individuals who are not immunocompromised are highly resistant to infection by the bacteria. Immunocompromised humans such as pregnant women or the elderly are highly susceptible to virulent Listeria. Abortion, premature birth or stillbirth is often the consequence of listeriosis in pregnant females. When the newborn is infected at the time of delivery listeriosis symptoms typically are these of meningitis and they begin 1- 4weeks after birth. Following invasion of macrophages virulent strains of Listeria may then multiply, resulting in disruption of these cells and septicimia. At this time the organism has access to all parts of the body. Death is rare in healthy adults; however, the mortality rate may approximate 30% in the immunocompromised, newborn or very young. Mode of transmission and associated foods :Foods involved include raw milk, soft cheese, meat-based paste, fresh and frozen meat, poultry and sea food products and raw fruit and vegetables. Reservoir/source: the Listeria bacteria are widely distributed in nature and can be found in decaying vegetables and in soils, animal feces, sewage, water, silage and faeces of numerous wild and domestic animals. Other sources may be infected animals and people. Other bacteria that cause food poisoning (less common bacteria) 41 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein 1. Enteropathogenic E.coli: A- ETEC (which cause syndroms like cholera) B- EHEC.O157H:7 2. Shigella-Endotoxins: (shiga toxins). 3. Yersinia enterocolitica (Endotoxins) causes Yersiniosis. 4. Vibrio parahaemolyticus. (Causes Gastroenteritis). 5. Campylobacter jejuni. (Causes Campylobacteriosis). 1-A Enterotoxigenic Escherichia coli (ETEC) Enterotoxigenic Escherichia coli (ETEC) are bacteria that cause disease in humans and domestic animals by producing a heat labile or heat stable toxin or both. Enterotoxigenic Escherichia coli (E. coli), or ETEC, is an important cause of bacterial diarrheal illness. Infection with ETEC is the leading cause of travelers' diarrhea and a major cause of diarrheal disease in lower-income countries, especially among children. ETEC is transmitted by food or water contaminated with animal or human feces. Food sources reported for ETEC-related diarrhea include fresh fruits and vegetables (especially lettuce), parsley, basil, scallops, shrimp, crab meat, tuna paste, prepared salads, and soft cheese. Contaminated water and food have been implicated as vehicles for transmission of ETEC infection. Infection can be prevented by avoiding or safely preparing foods and beverages that could be contaminated with the bacteria, as well as washing hands with soap frequently. What are the symptoms of ETEC? The main characteristic of the disease is a watery diarrhea. It begins about 14 to 50 hours after the bacteria have been ingested. The diarrhea may be mild and last only a few days or it may be more severe and prolonged, lasting up to three weeks. Generally the diarrhea does not contain blood or mucus. Other symptoms include:Abdominal cramps, Low-grade fever, Nausea, Headache and Muscle aches. The pathogenesis of ETEC-induced diarrhea is similar to that of cholera and includes the production of enterotoxins and colonization factors. 40 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein The clinical symptoms of ETEC infection can range from mild diarrhea to a severe cholera-like syndrome. The effective treatment of ETEC diarrhea by rehydration is similar to treatment for cholera, but antibiotics are not used routinely for treatment except in traveler's diarrhea. 1-B Enterohemorrhagic E. coli (EHEC): (Incubation period: 72-120 hrs). Escherichia coli are Gram negative enteric bacilli that are carried normally in the intestine of humans and animals. E. coli O157:H7 is the most common serotype of EHEC. Suspected foods: Cattle are the main source of infection. This disease is often associated with ingestion of inadequately cooked hamburger meat, raw milk, cream and cheeses made from raw milk. Pathogenesis: EHEC strains may produce one or more types of cytotoxins, which are collectively referred as Shiga-like toxins (SLT) since it is similar to Shiga toxin produced by Shigella dysenteriae. SLTs were previously known as verotoxin. The toxins kill colonic epithelial cells. Symptoms (Clinical features): Initial symptoms may be diarrhea with abdominal cramps, which may turn into bloody diarrhea in a few days. No fever occurs. 2- Shigella Shigella is a species of enteric bacteria that causes disease in humans and other primates. The disease caused by the ingestion of Shigella bacteria is referred to as Shigellosis, or ‘bacillary dysentery’ which is most typically associated with diarrhea (often bloody) and other gastrointestinal symptoms. Shigella is easily spread person-to- person because of its relatively tiny (compared to other bacteria) infectious dose. Infection can occur after ingestion of fewer than 100 bacteria. Another reason Shigella so easily cause infection is because the bacteria thrive in the human intestine and are commonly spread both by person-to-person contact and through the contamination of food. Shigella bacteria are generally transmitted through a fecal-oral route. Foods that come into contact with human or animal waste can transmit Shigella. Thus, handling toddlers’ diapers, eating 42 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein vegetables from a field contaminated with sewage, or drinking pool water are all activities that can lead to shigellosis 3-Yersinia enterocolitica Yersinia enterocolitica: is a Gram-negative bacillus- shaped bacterium that causes an infectious disease called yersiniosis. Yersinia enterocolitica is a member of the Yersinia family of bacteria. Common symptoms of yersiniosis in children (who most often contract the disease) are fever, abdominal pain, and diarrhea, which is often bloody. Symptoms typically develop 4 to 7 days after exposure and may last 1 to 3 weeks or longer. In older children and adults, right-sided abdominal pain and fever may be the predominant symptoms and may be confused with appendicitis. Yersiniosis is most often acquired by eating contaminated food, especially raw or undercooked pork products. The preparation of raw pork intestines may be particularly risky. Drinking contaminated unpasteurized milk or untreated water can also transmit the infection. 4- Vibrio parahaemolyticus V. parahaemolyticus is a Gram-negative curved rod, facultatively aerobic, non-spore forming, oxidase positive bacterium. It also has one polar flagellum contributing to its motility. Vibrio parahaemolyticus is a self-limiting, enterotoxic bacterium, typically causing acute gastroenteritis in humans. More severe cases of infection can occur in immune-compromised individuals, which can lead to septicemia and death, although this is very rare. Moderate to severe skin infections can also result from open wound exposure to V. parahaemolyticus in warm seawater, Vibrio parahaemolyticus is typically transmitted to human hosts through the 43 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein consumption of raw and undercooked shellfish including clams, muscles, and oysters, or drinking contaminated water. 5- Campylobacter jejuni These are small, curved-spiral Gram negative bacilli with polar flagella, appearing mainly in comma shape. Campylobacter are harbored in reproductive and alimentary tracts of some animals. Suspected foods: Transmission to humans occurs via a fecal-oral route, originating from farm animals, birds, dogs, and processed poultry, with chicken preparation comprising 50-70% of all campylobacter infections. The organism is transmitted to man in milk, meat products and contaminated water. Undercooked poultry and unpasteurized dairy are most often implicated as a source of it.The infective dose—that is, the amount of bacteria that must be ingested to cause illness—is relatively small. Ingestion of as few as 500 organisms, an amount that can be found in one drop of chicken juice, has been shown to cause human infection. Campylobacter jejuni has come to be understood as one of the leading causes of bacterial gastroenteritis. When a person is infected and develops symptoms, the illness is called Campylobacteriosis. “the incubation period varies from 2 to 7 days, a characteristic that is probably inversely related to the dose ingested.” Campylobacteriosis symptoms can range from diarrhea and lethargy that lasts a day to severe diarrhea and abdominal pain (and occasionally fever) that lasts for several weeks. Diarrhea and abdominal pain are the most common symptoms and the vast majority of cases are mild. Other typical symptoms of C. jejuni infection include fever, nausea, vomiting, abdominal pain, headache, and muscle pain. Campylobacter jejuni grows poorly on properly refrigerated foods, but does survive refrigeration and will grow if contaminated foods are left out at room temperature. The bacterium is sensitive to heat and other common disinfection procedures; pasteurization of milk, adequate cooking of meat and poultry, and chlorination or ozonation of water will destroy this organism. 44 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein Mycotoxins Mycotoxins are natural chemical substances (secondary metabolites) produced by fungi (molds) growing as contaminants on some food crops (in field and in storage), in particular cereals, nuts and fruit. Their presence in crops and in foods and animal feeds produced from them is undesirable, as they are toxic and have a number of adverse effects on health, both in humans and animals. Mycotoxins can affect the immune system, nervous system, liver,kidneys, and blood, and some mycotoxins are known to be carcinogens (cancer-causing). There is a major difference between the toxic metabolites of fungi and the toxins of most bacteria associated with food poisoning, the fungal toxins have relatively low molecular weight compounds, although their chemistry may be very complex, while the bacterial toxins are macromolecules such as polypeptides, proteins or lipopolysaccharides. The chemical and biological properties of the mycotoxins, as well as their toxic effects are extremly variable.Some mycotoxins were shown to be mutagenic, teratogenic, or/and carcinogenic. Exposure to mycotoxins The Food and Agriculture Organization (FAO) estimates that 25% of the world’s food crops, overall, are affected by mycotoxins. Considering that these food crops include cereals, nuts, fruit and vegetables which comprise a significant part of the European consumer’s diet, there is potentially a significant exposure to mycotoxins. Exposure of consumers to mycotoxins is mainly via plant foods. However, an additional potential exposure may be via foods of animal origin such as milk, cheese and meat, as a result of consumption of contaminated feed by food animals. This illustrates the need to control levels of mycotoxins in animal feed as well as food. The most common mycotoxins are aflatoxins, ochratoxin A, etc... Many foods and feeds including corn, wheat, barley, rice, oats, nuts, milk, cheese, peanuts and cottonseed can become contaminated with mycotoxins since they can form in commodities before harvest, during the time between harvesting and drying, and in storage. 45 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein The poisoning by mycotoxin is referred to as mycotoxicosis. A wide range of adverse and toxic effects in animals are produced by mycotoxin in addition to being food borne hazards to humans. TYPES OF MYCOTOXIN Mycotoxins have been reported to be carcinogenic, tremorogenic, haemorrhagic, teratogenic, and dermatitis to a wide range of organisms and to cause hepatic carcinoma in humans. More than a 100 species of filamentous fungi are known to cause toxic responses under naturally occurring conditions by producing mycotoxins. Mycotoxins can enter the human and animal food chains by direct contamination when the food has been contaminated by toxigenic fungi while growing or after harvest, or indirect contamination, for example in milk from cows fed with contaminated food. More than 300 mycotoxins are known, of which about 20 are serious contaminants of crops used in human foods and animal feeds. Mycotoxin contamination of foods and feeds depends highly on environmental conditions that lead to mould growth and toxin production. 1- Aflatoxin Aflatoxins are produced by three molds of the Aspergillus species: A. flavus (A+fla+toxin), A. parasiticus and A. nomius and various species of Penicillium, Rhizopus, Mucor and Streptomyces, which contaminate plants and plant products. 2-Ochratoxin-A (OTA) Ochratoxin-A: produced by the fungi Aspergillus ochraceus and Penicillium verrucosum. Isolates of Aspergillus niger as well as A. carbonarius are capable of producing OTA. OTA generally appears during storage of fresh produce (in cereals, coffee, cocoa, dried fruit, spices, and also in pork) and occasionally in the field on grapes. It may also be present in some of the internal organs (particularly blood and kidneys) of animals that have been fed on contaminated feeds. 3-Fusariotoxins (Fusarium toxins) Fungi belonging to the genus Fusarium are associated with the production of Fusariotoxins. 46 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein 4-Alternaria toxins Mycotoxins produced by fungi belonging to Alternaria species are referred to as Alternaria toxins. They commonly occur during the pre- and post harvest stages of fruits and vegetables. The most important toxin-producing species is Alternaria alternata, which usually contaminates cereals, sunflower seeds, olives, and fruits. 5-Claviceps purpurea/ergot toxins Sclerotia of fungi belonging to the genus Claviceps produce ergot alkaloids. A sclerotium is a dark-colored, hard mycelial mass that establishes itself on the seed or kernel of the plant. Usually, wild grass species are considered to favor the cross-contamination of C. purpurea onto the cultivated grass. Ergot reduces yield because seeds or kernels are replaced by sclerotia. Ergot produced by the mold Claviceps purpurea, which can cause ergotism in humans and other mammals who consume grains contaminated with its fruiting structure (ergot sclerotium). 6-Patulin It is a mycotoxin produced by a variety of molds, in particular, Penicillium expansum. Most commonly found in rotting apples. In addition, patulin has been found in other foods such as grains, fruits, and vegetables. While not considered a particularly potent toxin, a number of studies have shown patulin to be genotoxic, which has led some to theorize that it may be a carcinogen. Patulin has shown antimicrobial properties against some microorganisms. It is heat- stable, so it is not destroyed by pasteurization or thermal denaturation.Patulin has also become important to apple processors as a method for monitoring the quality of apple juices and concentrates. The presence of high amounts of patulin indicates that moldy apples were used in the production of the juices. Patulin is being considered as a “possible toxin” and is regarded as the most dangerous mycotoxin in fruits, particularly apples, pears, and their products. Patulin is mainly associated with surface-injured fruits, which renders them vulnerable to fungal infection, mainly by Penicillium spp. 47 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein 7-Citrinin It is produced by the mold Penicillium citrinum , Citrinin acts as a nephrotoxin.It causes mycotoxic nephropathy in livestock and has been implicated as a cause of Balkan nephropathy (referred to as "yellow rice disease") in humans. Citrinin is used as a reagent in biological research. It induces mitochondrial permeability pore opening and inhibits respiration. It has been found on human foods, such as grains and cheese.Citrinin often occurs as a common contaminant of food and feed (fruits, barley, maize, cheese, dietary supplements). Production of Mycotoxins Several factors influence mold development, including moisture, temperature, aeration and substrate. Moisture is probably the most important of these factors but the type of mold and whether or not a toxin is produced will depend on the interplay of all these factors.Physical damage, such as breakage and stress cracks in grain, will increase the likelihood of fungal growth. High moisture corn, especially if ground, is highly susceptible to fungal invasion and toxin formation. To prevent production of the toxin on harvested products, care should be taken to prevent physical damage at harvest and to reduce the moisture level soon after harvesting. Rapid ensiling or the addition of organic acids will aid in preventing the formation of additional mycotoxin. 48 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein Lec 7: General Principles of food Preservation Foods for human consumption can be divided into 4 plant and 4 animal origin as well as other additive materials. Food from plants Food from animals Cereals and cereal products. Meat and meat products. Sugar and sugar products. Poultry and eggs. Vegetables and vegetable products. Fish and other sea food. Fruit and fruit products. Milk and milk products. To the list of plant origin it may also contain spices and other flavoring materials, like sodium chloride which is a mineral and flavoring material, an essential nutrient and a chemical preserver. Some foods may be fortified with minerals such as iron and calcium which are added to flour. Some of the coloring and flavoring materials used in food are synthetic. Vitamins usually are presented in foods but may be added or consumed separately after chemical synthesis or production by M.O. Food preservation: is a set of physical, chemical and biological processes that are performed to prolong the shelf life of foods and at the same time retain the features that determine their quality, like color, texture, flavor and especially nutritional value. Food preservation is achieved by destroying enzymes and microorganisms using heat (blanching, pasteurization), or preventing their action by: removal of water, or increasing acidity or using low temperatures. Most kinds of foods are readily to be decomposed by M.O unless special methods are used for preservation. Methods of food preservation Method Procedure Antimicrobial Typical material surviving microbes Physical High temp. - Thermophil 49 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein bacteria , spores Low temp. - Psycrophiles Water content - Xerophiles Irradiation - spores Filtration - Depending on further preservative methods Chemical salting NaCl Halophilic bacteria Curing Nitrites G+ve bacteria Smoking Phenoles ,acids Depending on further preservative methods Preservatives Organic acids Bacteria tolerate acids Biological Fermentation Organic acids Depending on ecological factors Principles of food preservation: To accomplish the preservation of foods by the various methods, the following principles of prevention or delay of decomposition should be involved: 1. CONTROLLING MICROORGANISMS BY: A. Keeping microorganisms out of food, e.g.: Asepsis. B. Removing microorganisms from food, e.g.: Filtration. C. Delaying microbial growth, e.g.: low temp., drying, anaerobic conditions or chemicals. D. Killing microorganisms or spores, e.g. Heat or irradiation. 2. CONTROLLING ENZYMES BY: A. Inactivating endogenous enzymes, e.g.: blanching. B. Preventing or delaying chemical reactions in the food, e.g.: prevention of oxidation by means of antioxidants. 51 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein 3. CONTROLLING INSECTS, RODENTS, BIRDS AND OTHER PHYSICAL CAUSES OF FOOD DETERIORATION. It’s very important in food preservation (i.e.preservation of spoilage) is the lengthening, as much as possible of the lag phase and the phase of positive acceleration. Food protection with low temperature Physical Methods: Non-Thermal processing The application of extreme heat treatments used for food preservation affect the nutritional and organoleptic properties of food. In recent years, the consumers demand for fresher, higher quality and safe food has increased. Therefore, nonthermal methods of food preservation for the inactivation of microorganisms and enzymes as an alternative to thermal processes are being used. However, the high resistance of certain enzymes and microorganisms to nonthermal processes, especially bacterial spores, limit their application. During nonthermal processing, the temperature of foods is held below the temperature normally used in thermal processing; therefore, a minimal degradation of food quality is expected. Nonthermal process of food preservation improves food quality and enhances safety levels. Overall, most nonthermal preservation techniques are highly effective in inactivating vegetative cells of bacteria, yeast, and molds. Bacterial spores and most enzymes are however, difficult to inactivate with these procedures. Thus their use is limited to foods where enzymatic reactions do not affect food quality or where spore germination is inhibited by other prevailing conditions, such as low pH. Low Temperature Preservation Storage at low temperatures prolongs the shelf life of many foods. In general, low temperatures reduce the growth rates of microorganisms and slow many of the physical and chemical reactions that occur in foods. Low temperatures are used to preserve food by lowering microbial activity through the reduction of microbial enzyme activity. However, psychrotrophic bacteria are known to grow even at commercial refrigeration temperatures (70C). These 50 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein bacteria include members of the genera Pseudomonas, Alcaligenes, Micrococcus and Flavobacterium. Some of the fungi also grow at refrigeration temperatures. Slow freezing and quick freezing are used for long-term preservation. Freezing reduces the number of microorganisms in foods but does not kill all of them. In microorganisms, cell proteins undergo denaturation due to increasing concentrations of solutes in the unfrozen water in foods, and damage is caused by ice crystals. Refrigeration Refrigeration slows down the biological, chemical, and physical reactions that shorten the shelf life of food. Exposure of microorganisms to low temperatures reduces their rates of growth and reproduction. This principle is used in refrigeration and freezing. Microbes are not killed at refrigeration temperature for a considerable period of time. In refrigerators at 5°C, foods remain unspoiled but in a freezer at -5°C the crystals formed tear and shred microorganisms. It may kill many of the microbes. However, some are able to survive. Salmonella spp. and Streptococcus spp. Survive freezing. For these types of microorganisms rapid thawing and cooking is necessary. Refrigerators should be set to below 12°C to control the growth of micro-organisms in foods. This lowered temperature also reduces the respiration rate of fruits and vegetables, which retards reactions that promote spoilage. All perishable foods should be refrigerated as soon as possible, preferably during transport, to prevent bacteria from multiplying. Refrigeration is generally used to: i) reduce spoilage during distribution of perishable foods, ii) increase the holding period between harvesting and processing; and iii) extend the storage life of commercially processed foods. All foods are not benefited from cold temperatures. For example, bananas turn black when refrigerated. Freezing Freezing is also one of the most commonly used processes commercially and domestically for preserving a very wide range of food stuffs including prepared food stuffs which would not have required freezing in their unprepared state. For example, potato waffles are stored in the freezer, but potatoes themselves require only 52 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein a cool dark place to ensure many months storage. Freezing makes water unavailable to microorganisms. The chemical and physical reactions leading to deterioration are slowed by freezing. White or grayish patches on frozen food caused by water evaporating into the packages air spaces called freezer burn occurs which causes deterioration of taste and appearance. This occurs in fruits, vegetables, meat, poultry and fish. While many home freezers are held at -10°C, commercial freezers are under -18°C. At this temperature, the growth of micro-organisms is almost stopped. Deteriorative microbial reactions will still occur, but over a much longer time. In addition, deteriorative enzymatic reactions will still take place during frozen storage. Uncooked fruits and vegetables must be blanched before freezing to prevent these reactions. During freezing, the water in food forms ice crystals. The rate of this phenomenon has a big impact on the quality of frozen foods: Slow freezing (e.g. home freezer) forms large ice crystals which puncture cell walls and cellular fluid is released and also results in shrunken appearance of thawed food. In this process the freezing is done for 3-72 h. This method is used in home freezer and temperature is lowered to -15 to -29°C. Rapid freezing During rapid freezing small, numerous ice crystals are formed and cell structure is not changed. In this process the temperature of food is lowered to about -20°C within 30 min. This process blocks or suppresses the metabolism. The shelf life of frozen foods is largely dependent on storage conditions. Under ideal conditions, frozen foods can have a shelf life of one year. However, if foods are continuously exposed to warmer temperatures, such as the opening and closing of freezer doors, then heat shock occurs. Heat shock is when ice melts and re-forms into larger ice crystals. The best example is ice cream, which has a gritty texture if large ice crystals have developed. Advantages of freezing are generally good retention of nutrients and prevention of microbial growth by low temperature and unavailability of water. However, disadvantages of freezing are loss of some B- Group vitamins and vitamin C due to blanching of vegetables prior to freezing and unintended thawing can reduce product quality. Preservation by Freeze Drying 53 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein The process of freeze drying or lyophilization is commonly used these days for preservation. The food is deep frozen, after which the water is drawn off by a vacuum pump in a machine. The dry product is then sealed in foil and is reconstituted with water. This method is very useful for storing, transporting and preserving bacterial cultures. Drying or dehydration involves the removal of water from the food by controlled processes. This may be done by evaporation due to heating of the product, e.g., drying of fruits, osmotic dehydration, e.g. brining of fish and sublimation, or freeze drying e.g. in the drying of coffee. There are two distinct stages in this technology. In the first stage, the removal of surface water depends solely on the state of the air surrounding the food, such as its temperature, relative humidity and speed. In the second phase of drying, the moisture within the food moves to the surface. As the air is heated, its relative humidity decreases, resulting in more absorption of water. Here the rate of drying is dependent on the time the moisture takes to get to the surface. The heating of the air around a food product can, therefore, cause it to dry more quickly. The principle of sublimation is used in freeze drying and lyophilization. This is the process in which a solid changes directly to a vapor without passing through the liquid phase. 54 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein Lec 8 : Food Protection at High Temperature The killing of microorganisms by heat is supposed to be caused by the denaturation of proteins and especially by the inactivation of enzymes required for metabolism. Physical Methods-Thermal Processing Heat kills microorganisms by changing the physical and chemical properties of their proteins. When heat is used to preserve foods, the number of microorganisms present, the microbial load , is an important consideration. Various types of microorganisms must also be considered because different levels of resistance exist. For example, bacterial spores are much more difficult to kill than vegetative bacilli. In addition, increasing acidity enhances the killing process in food preservation. HIGH TEMPERATURE Three basic heat treatments are used in food preservation: pasteurization , in which foods are treated at about 62°C for 30 minutes or 72°C for 15 to 17 s; hot filling , in which liquid foods and juices are boiled before being placed into containers; and steam treatment under pressure, such as used in the canning method. Pasteurization It is the process of heating a food-usually a liquid-to or below its boiling point for a defined period of time. The purpose is to destroy all pathogens, reduce the number of bacteria, inactivate enzymes and extend the shelf life of a food product. Pasteurization treatment is able to kill most heat resistant non spore forming organisms like Mycobacterium tuberculosis and Coxiella burnetti. Foods with a pH of less than 12.6, such as milk and spaghetti sauce, can be pasteurized. Permanent stabilitythat is, shelf life of about two years is obtained with foods that can withstand prolonged heating, such as bottled juices. There is a greater loss of flavour from foods that are exposed to a longer time-temperature relationship. Therefore, temporary stability (that is, limited shelf life) is only obtained with some foods where prolonged heating would destroy its quality. These foods, such as milk, usually require subsequent refrigeration. "High Temperature Short Time" (HTST) and "Ultra High Temperature" (UHT) processes have been developed to retain a food's texture and flavour quality parameters. Pasteurization is not intended to kill all microorganisms in the food. Instead pasteurization aims to reduce the number of viable pathogens so that they are unlikely to cause disease. Pasteurization involves a comparatively low order of heat treatment, generally at temperature below the boiling point of water.. Desired pasteurization can be achieved by a combination of time and temperature such as heating food to a low temperature and maintain for a long time i.e.Low temperature long time LTLT -62.8 0 C for 30 minute, or by heating food to a high temp and maintain for a short time: HTST-71.7 0 C for 15 second. Pasteurization is used when more rigorous heat treatment might harm the quality of the food product, as the market milk and for the main spoilage organisms which are not heat resistant, such as yeast in fruit juice. It also kills the pathogens. 55 Biology 4th stage Food Microbiology 2024-2023 Dr. Marwa H. ALKhafaji & Dr. Alyaa R.Hussein Ultra heat pasteurization In this process milk is heated to 120-138 0 C for 2-4 seconds and followed by rapid cooling. This treatment kills all the spoilage microorganisms. UHT pasteurized milk is packaged aseptically resulting in a shelf stable product that does not require refrigeration until opened. Heat resistance of microorganisms and their spores It is expressed in terms of their thermal death time (TDT). Thermal Death Time (TDT) It is the time taken to kill a given number of microorganisms or spores at a certain temperature under specified conditions. Thermal death point It is the temperature necessary to kill all the organisms in ten minutes. Heat resistance of different microorganisms i

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