Micro Chapter 4 PDF

Chapter 4 Food & Industrial Microbiology  Microorganism Growth in Food Foods are not only of nutritional value to those who consume them but often are ideal culture media for microbial growth Provides carbon sources (amino acids, amines, ketones, gases, organic acids, and alcoho...

Chapter 4 Food & Industrial Microbiology  Microorganism Growth in Food Foods are not only of nutritional value to those who consume them but often are ideal culture media for microbial growth Provides carbon sources (amino acids, amines, ketones, gases, organic acids, and alcohols) , electron donors, electron acceptors, etc. Factors affecting microbial growth in food: A- Intrinsic Factors: factors related to the food itself i. Food composition and pH ii. Presence and availability of water iii. Oxidation-reduction potential iv. Physical structure v. Presence of antimicrobial substances i. Composition and pH Carbohydrates do not result in major odors Proteins and/or fats result in a variety of foul odors (e.g., putrefactions). Putrefaction: proteolysis and anaerobic breakdown of proteins, yielding foul-smelling amine compounds Low pH: favors yeasts and molds and high pH favors bacteria High pH: favors putrefaction ii. Water availability – Can be measured in terms of water activity (aw) – In general, lower water activity inhibits microbial growth Can be achieved by: Drying and Addition of salt or sugar Osmophilic Microorganisms: prefer high osmotic pressure Xerophilic Microorganisms: prefer low water activity iii. Oxidation- Reduction potential – Presence of electron donor and acceptor – Can be altered by cooking – High oxidation-reduction potential favors aerobic and facultative anaerobic bacteria iv. Physical structure – grinding and mixing increase surface area and distribute microbes promotes microbial growth – outer skin of vegetables and fruits slows microbial growth v. Antimicrobial substances: complex chemical inhibitors & enzymes – coumarins – fruits and vegetables – lysozyme – cow’s milk and eggs – aldehydic and phenolic compounds – herbs and spices – Allicin and eugenol – garlic and cloves – polyphenols – green and black teas B- Extrinsic Factors: Environmental conditions in which the food is stored i. Temperature  lower temperatures retard microbial growth ii. Relative humidity  higher levels promote microbial growth iii. Atmosphere (Oxygen and Carbon dioxide gases)  Oxygen promotes growth  Excess CO2 can decrease the solution pH, inhibiting microbial growth  Modified Atmosphere Packaging (MAP) o use of shrink wrap and vacuum technologies to package food in controlled atmospheres e.g., at about 60% CO2 and low level of oxygen content  11.2. Microbial growth and Food spoilage Food spoilage - visible changes in colors, flavor, odor, texture - involves predictable succession of microbes Ex. four steps of spoilage in unpasteurized milk o Lactococcus lactis subsp. lactis (1st), Lactobacillus (2nd), Yeasts and Molds (3rd), Bacteria (4th) different foods undergo different types of spoilage processes  Toxins are sometimes produced – Ergot alkaloid (ergotism)  toxic condition caused by growth of a fungus (Claviceps purpura) in grains – Aflatoxins  carcinogens produced in fungus- infected grains (Aspergillus flavus) and nut products – Fumonisins  carcinogens produced in fungus- infected corn (Fusarium moniliforme) – Algal toxins  may contaminate shellfish and finfish  11.3. Controlling food spoilage: Food Preservation Purpose:- To eliminate or reduce the populations of spoilage and disease causing microbes - To maintain the microbiological quality of a food with proper storage and packaging - There are seven basic approaches of preservation 1- Removal of Microorganisms – usually achieved by pre-filtration and centrifugation – commonly used for water, beer, wine, juices, soft drinks, and other liquids 2- Low Temperature – refrigeration at 5°C retards but does not stop microbial growth – microorganisms can still cause spoilage with extended spoilage – growth at temperatures below -10°C has been observed 3- High Temperature A-Pasteurization- kills pathogens and substantially reduces number of spoilage organisms a) conventional Low-temperature holding (LTH) pasteurization- treatment at 62.8°C for 30 minutes b) High-temperature, short-time (HTST) process- treatment at 71°C for 15 seconds; c) Ultra-high-temperature (UHT) processing- treatment at 141°C for 2 seconds B-Canning: kills spoilage microbes, but not necessarily all microbes in food – food heated in special containers (retorts) to 115°C for 25 to 100 minutes – Spoilage of canned goods spoilage prior to canning underprocessing leakage of contaminated water into cans during cooling process 4- Reduced water availability: Dehydration – Drying – Freeze-drying (lyophilization) – Addition of high concnetrations of solutes such as sugar or salt 5- Chemical-Based Preservation – Listed as chemical agents “generally recognized as safe”: GRAS Ex. simple organic acids, sulfite, ethylene oxide as a gas sterilant, sodium nitrite, and ethyl formate. – Disrupt a critical cell factor Ex. damage the plasma membrane or denature various cell proteins, interfere with the functioning of nucleic acids, thus inhibiting cell reproduction 6- Radiation A- ultraviolet (UV) (non-ionizing) radiation used for surfaces of food-handling equipment does not penetrate foods B- radappertization (gamma radiation) use of ionizing radiation (gamma radiation) to extend shelf life or sterilize meat, seafoods, fruits, and vegetables kills microbes in moist foods by producing peroxides from water 7- Microbial Product-Based Inhibition – Bacteriocins: bactericidal proteins active against related species – some dissipate proton motive force of susceptible bacteria – some form pores in plasma membranes – some inhibit protein or RNA synthesis – e.g., nisin: used in low-acid foods to inactivate Clostridium botulinum during canning process Basic Approaches to Food Preservation: summary 1- 2- 3- 4- 5- 6- 7-  11.4. Food Borne Diseases Two primary types of food related disease on the basis of toxin production by bacteria: 1. Food-Borne Infections – Ingestion of microbes, followed by growth, tissue invasion, and/or release of endotoxins inside the host – Onset of symptoms after incubation time as short as 8hrs to 2weeks – Include Salmonellosis, Shigellosis, Gastroenteritis, Listeriosis, Diarrhea by E. coli O157: H7 2. Food-Borne Intoxications – Ingestion of exotoxins released by microbes in foods in which the microbes have grown – Produces symptoms shortly after consumed (with in 2-6hrs) since growth of disease causing microbe is not required – include staphylococcal food poisoning, botulism, Clostridium perfringens food poisoning, and Bacillus cereus food poisoning Detection of Food-Borne Pathogens 1. culture techniques 2. immunological techniques - very sensitive 3. molecular techniques probes used to detect specific DNA or RNA sensitive and specific  11.5. Microbiology of Fermented Foods Several of the fermented products we consume depend upon yeast fermentation of glucose to ethanol. 1. Alcoholic Beverages 2. Bread 3. Dairy Products 4. Other Fermented Foods Alcoholic Beverages (ex. Beer and wine) – Alcohol is produced from fermentation by the yeast Saccharomyces cerevisiae Beer Processing Wine Processing  Bread – involves growth of Saccharomyces cerevisiae (baker’s yeast) under aerobic conditions – maximizes CO2 production, which leavens bread – can be spoiled by Bacillus species that produce ropiness Dairy Products – At least 400 different fermented milks are produced throughout the world; – fermentations are carried out by mesophilic, thermophilic, and therapeutic lactic acid bacteria, as well as by yeasts and molds. i. Mesophilic- acid produced from microbial activity at temperatures lower than 45°C causes protein denaturation (e.g., cultured buttermilk and sour cream) ii. Thermophilic-fermentations carried out at about 45°C (e.g., yogurt) iii. Therapeutic-fermented milks may have beneficial therapeutic effects (e.g.,Bifid-amended fermented milk products)  Yogurt – Milk is fermented by a mixture of Streptococcus salivarius ssp thermophilus and Lactobacillus bulgaricus (official name Lactobacillus delbrueckii ssp. bulgaricus). – Often these two are co-cultured with other lactic acid bacteria for taste or health effects (probiotics). These include L. acidophilus, L. casei and Bifidobacterium species. – Acid produced from the fermentation causes the protein in the milk (casein) to coagulate into a semisolid curd. Cheese Milk is treated with lactic acid bacteria and an enzyme called rennin that partially hydrolyses the protein and causes it to coagulate into “curds.” The liquid portion of the milk at this time is called “whey.” The whey is separated from the curds, and the curds are aged (“ripened”) Different microbes in the early and late stages of processing give rise to cheeses with different characteristics  Other fermented foods – Sausages - hams – Bologna - salami – izushi – fish, rice, and vegetables - sauerkraut – katsuobushi – tuna Microorganisms and food Amendments (sources) Besides microorganisms’ actions in fermentation as agents of physical and biological change, they themselves can be used as animal and human food sources: Single Cell Proteins Ex. Mushrooms (Agaricus bisporus), Cynanobacteria (Sypirilluna)  Industrial Microbiology and Biotechnology Involves the use of microorganisms to produce an industrial product in large quantities through genetic modifications, particularly by recombinant DNA technology Ex. anticoagulants, antidepressants, vasodilators, herbicides, insecticides, plant hormones, enzymes, and vitamins The use of microorganisms in industrial microbiology and biotechnology follows a logical sequence. 1. Identify or choose a microorganism that carries out the desired process in the most efficient manner from nature. 2. Genetic manipulations to produce microorganisms with new and desirable characteristics 3. Preservation in its original form  Genetic manipulation of microorganisms Genetic manipulations are used to produce microorganisms with new and desirable characteristics. It can be done in a variety of ways including: 1. Mutation- once a promising culture is found, it can be improved by mutagenesis with chemical agents and UV light 2. Protoplast fusion-widely used with yeasts and molds, especially if the microorganism is asexual or of a single mating type;  involves removal of cell walls, mixing two different solutions of protoplasts, and growth in selective media.  Can also be done using species that are not closely related 3. Insertion of short DNA sequences- Short lengths of chemically synthesized DNA sequences can be inserted into recipient microorganisms by site- directed mutagenesis  leads to small changes in amino acid sequence, but these can result in unexpected changes in protein characteristics;  site-directed mutagenesis is important to field of protein engineering 4. Transfer of Genetic Information between Different Organisms: involves the transfer of genes for the synthesis of a specific product from one organism into another, giving the recipient varied capabilities such as an increased capacity to carry out hydrocarbon degradation by combinatorial biology. Ex. the genes for antibiotic production can be transferred to a microorganism that produces another antibiotic, or even to a non-antibiotic-producing microorganism. Preservation of Microorganisms Once a microorganism or virus has been selected or created to serve a specific purpose, it must be preserved in its original form for further use and study. – Lyophilization, or freeze-drying, – Storage in liquid nitrogen  Microbial products Microbes in industrial fermentation produce two types of products A. Primary metabolites: are related to the synthesis of microbial cells in the growth phase;  include amino acids, nucleotides, exoenzymes and fermentation end products such as ethanol and organic acids,  These enzymes find many uses in food production and textile finishing. B. Secondary metabolites: usually accumulate in the period of nutrient limitation or waste product accumulation that follows active growth  These compounds have no direct relationship to the synthesis of cell materials and normal growth.  include antibiotics and mycotoxins  Major Products of Industrial Microbiology In commercial industrial plants (bioreactors), microorganisms are widely used to produce numerous organic materials that have far-reaching value and application  Bioreactors: Vessels for industrial fermentation; they are designed with close attention to aeration, pH control, and temperature control. o There are many different designs, but the most widely used bioreactors are of the continuously stirred type Commercial use of major products Organic Acids Enzymes  Other products Specialty compounds for use in medicine and health-include sex hormones, ionophores, and compounds that influence bacteria, fungi, amoebae, insects, and plants Biopolymers-microbially produced polymers ex. Polysaccharides, are uses as stabilizers, as blood expanders and absorbents, to make plastics, as food thickeners; to enhance oil recovery from drilling mud and for different fibers, eg, Jeans. Biosurfactants- have increased biodegradability, ex. glycolipids, Bioconversion processes -microbial transformations or biotransformations where Microorganisms are used as biocatalysts;  Biotechnological Applications Biosensors: living microorganisms (or their enzymes or organelles) are linked with electrodes, and biological reactions are converted into electrical currents to detect specific substances – have been developed to measure specific components in beer, to monitor pollutants, to detect flavor compounds in foods, and to detect glucose and other metabolites in medical situations. – New immunochemical-based biosensors are being developed; these are used to detect pathogens, herbicides, toxins, proteins, and DNA Biopesticides: biological agents, such as bacteria, fungi, viruses, or their components, which can be used to kill a susceptible insect.  This is accomplished by inserting toxin-encoding gene into plant or by production of a wettable powder that can be applied to agricultural crops  Bacteria e.g., Bacillus thuringiensis Microarrays: Arrays of genes that can be used to monitor gene expression in complex biological systems.  offers the potential of assaying all genes used to assemble an organism and can monitor expression of multiple genes  Commercial microoarrays are now available for Saccharomyces cerevisiae and Escherichia coli Chapter 5 Medical Microbiology