Advanced Certificate in Nutrition - Foodborne illness and food preservation - PDF

Advanced Certificate in Nutrition Foodborne illness: Virus, Mold, and Protozoa Dr. Rachel Ching [email protected] 1 Learning outcome • Recognize the characteristics, reservoir, mode of transmission, associated illness of the microorganisms (virus, mold, and protozoa) that commonly cause foodb...

Advanced Certificate in Nutrition Foodborne illness: Virus, Mold, and Protozoa Dr. Rachel Ching [email protected] 1 Learning outcome • Recognize the characteristics, reservoir, mode of transmission, associated illness of the microorganisms (virus, mold, and protozoa) that commonly cause foodborne illness 2 Viral foodborne illnesses • Virus § Microscopic parasite § Generally, much smaller than bacteria § Only replicate inside the living cells of organisms § Infect host cells to reproduce • Human usually get infected with virus via § Ingestion and then shed in feces § Contaminated water sources § Flies (not important) 3 Viral foodborne illnesses • Food contamination 1. Primary contamination • Food can be naturally contaminated during primary production § E.g. Filter-feeding shellfish most common food contaminated at water source § E.g. Fruit or vegetable contaminated with polluted water during irrigation 2. Secondary contamination • Contamination caused by food handlers, carriers or the contaminated food preparation area 4 Common viruses causing foodborne illness 1. Norovirus 2. Rotavirus 3. Hepatitis A virus 1. Norovirus 諾如病毒 Characteristics RNA virus • 3 - 35nm in diameter • Account for almost one-third of the non-bacterial gastroenteritis • Also known as “winter vomiting bug” Growth • • Relatively resistant to heat, disinfection and pH changes Survive freezing and high temperature (up to 60°C) Types of illness • Infection Reservoir • Human Mode of transmission • • • • • Mainly transmitted between hand and mouth contact (e.g. Fecal-oral transmission) Direct contact (like shaking hand) with the infected persons Touch the contaminated surface Raw or inadequate cooked shellfish especially bivalve mollusks (e.g. oyster) Salad made with contaminated fruits and vegetables Onset time 1-2 days Symptoms • • • • • • Vomiting Diarrhea Mild fever Nausea Stomach pain Easily infect children and elderly people 6 7 2. Rotavirus 輪狀病毒 Characteristics RNA virus • 70nm in diameter • Major cause of gastroenteritis in infants and children Growth • Relatively resistant to heat, disinfection and pH changes Types of illness • Infection Reservoir • Human • • • • Fecal-oral transmission Person-to-person transmission Food and waterborne Caused by cross contamination of food handlers in preparing ready-to-eat foods e.g. salad, finger foods, etc Mode of transmission Onset time 1-3 days Symptoms • • • • • Vomiting Diarrhea Nausea Fever Death only found in severe cases 9 3. Hepatitis A Virus 甲型肝炎病毒 Characteristics RNA virus • 27nm in diameter • Cause viral liver infection - common around the world Growth • Relatively resistant to heat, disinfection and pH changes Types of illness • Infection Reservoir • Human Mode of transmission • • • Fecal-oral transmission Person-to-person transmission Raw or undercooked shellfish Onset time 12-50 days • Symptoms • First phase • Fatigue, diarrhea with liver symptoms e.g. yellowing of the skin and the whites of your eyes, pale-colored feces, dark urine Second phase • Extensive liver damage, associated with colonization of liver 10 Mold toxins occurring in foods • Molds § Primarily soil organism § Many produce toxins – called mycotoxins § Food spoiled by molds may contain mycotoxins Molds • Mycotoxin related foodborne illness 1. Ergot poisoning 2. Aflatoxin poisoning 12 1. Ergot poisoning ⿆⾓中毒 • Ergot § A group of molds produce toxins that affect neurons • Genus Claviceps § Claviceps purpurea • Plant pathogen • Grows inside rye 黑麥 and sometimes wheat kernels • Forms sclerotium (fruiting structure) § Lightly curved, black to purple kernel § Contain neuron toxin 13 1. Ergot poisoning ⿆⾓中毒 • Ergot poisoning § Toxin is absorbed in the intestines § Transported to neurons § Peripheral neuron degenerate à tissue degenerate • Illness § Ergotism • Symptoms § Vision problems, confusion, unconsciousness, and gangrene in toes and fingers 14 2. Aflatoxin poisoning Aspergillus flavus and other Aspergillus species § Grow in grains and nuts to produce toxins • Damp and warm condition § Aflatoxin • Lipid soluble • Not destroyed by normal cooking conditions • Carcinogenic § Present in animals' feeds (e.g. cottonseed, corn, rice, soybean) as well as food sources of human (e.g. peanuts, livestock, cow milk) 15 2. Aflatoxin poisoning • Mode of transmission § Contaminated animal feeds (e.g. cottonseed, corn, rice, soybean) § Contaminated food sources of human (e.g. peanuts, livestock, cow milk) • Symptom § Liver degeneration § Liver tumor § Stunted growth in children 16 Common protozoa causing foodborne illness • Ciguatera food poisoning: A foodborne illness caused by eating reef fish (e.g. tiger grouper contaminated with toxins called Ciguatoxins • Ciguatoxin Parasites (Protozoa) § Heat-stable § Lipid-soluble neurological toxin § Accumulated in fish tissues • Toxin produced by dinoflagellate Gambierdiscus toxicus 17 Common protozoa causing foodborne illness • Symptoms § Appear within 3-5 hours after consumption § Death is uncommon § Gut illness: Vomiting, diarrhea, abdominal pain § Weakness § Muscle pain § Itching § Headache § Sweating § Dizziness § Neurological numbness and tingling around lips, hands, feet 18 Advanced Certificate in Nutrition Food preservation Dr. Rachel Ching [email protected] 19 Learning outcome • Recognize the objectives of food preservation • Understand the mechanism of different food preservation methods, and how each method manipulates the factors necessary for the growth of microorganisms • Recognize the differences between pasteurization and sterilization • Recognize the kinetics of thermal destruction of microorganisms 20 Food preservation • The process of treating and handling food to stop or slow down food spoilage, loss of quality, edibility, or nutritional value and thus allow for longer food storage 21 The objectives of food preservation • Prevent spoilage of food and food products and extend their shelf life § Minimize or inactivate spoilage microorganisms • Ensure the safety of food products § Inactivate harmful pathogens present in the food 22 Principles of food preservation • Elimination or inactivation of microorganisms § E.g. using heat to kill the microorganisms in food • Stopping the action of enzymes § To reduce the self-decomposition of food • Prevention of oxidation § To reduce the rate of lipid oxidation 23 Methods of food preservation • Food preservation methods § Manipulating one or more intrinsic or extrinsic factors § Slowing down microbial growth or inactivating (killing) microorganisms 24 How to control microbial growth • Intrinsic factors § Water activity § pH § Redox potential § Nutrient content • Extrinsic factors • Temperature • Atmosphere • Relative humidity Which factors can be manipulated? 25 Methods of food preservation A. Physical methods • • • • • • Heating Low temperature Dehydration Modified atmosphere packaging Radiation Filtration B. Chemical methods • • • • Addition of acid Addition of salt Addition of sugar Other food preservatives C. Biological methods • Fermentation 26 A. Physical methods of food preservation 27 Heat treatment - 1. Pasteurization • Pasteurization is a thermal process used to inactivate enzymes and eliminate viable pathogenic microorganisms from heat sensitive food § E.g. Milk, fruit juice, wine, egg • Relatively mild heat treatment • Food is heated to < 100˚C for a definite length of time, and then cooled immediately to slow down microbial growth in food • Refrigeration storage needed with 2-3 weeks shelf life 28 Heat treatment - 1. Pasteurization • The process involves two steps: heating and cooling • Different time-temperature combination § Low temperature pasteurization • 63˚C for 30 minutes § High temperature short time (HTST) pasteurization • E.g. 72˚C for 15 seconds • Shorten the heating time can better retain nutritional and sensory quality 29 Heat treatment - 1. Pasteurization A. HTST pasteurization of raw milk § Or called traditional pasteurization § Heating the milk briefly to 72 °C for about 15 seconds, to kill disease-causing microbes (e.g. Salmonella, Escherichia coli O157, Campylobacter) that can be found in raw milk § Followed by rapid cooling (4 °C) § Refrigeration storage needed Link - production of pasteurized milk 30 Heat treatment - 1. Pasteurization B. Ultra-high temperature (UHT) pasteurization of raw milk § Heating milk to ~138 °C for 2-3 seconds, then rapidly cooling it down § Milk is packaged in sterile, hermetically-sealed container (Aseptic packaging) § Refrigeration is NOT required until opened § Shelf stable for 6 months § Undesirable effect on the taste of milk – cooked, burnt taste 31 Heat treatment - 1. Pasteurization 72˚C UHT milk 32 Heat treatment – 2. Sterilization • Sterilization § A process completely kills or removes all life forms, including bacteria and other organisms (E.g. endospores) in the material or an object § Heating is the most commonly used method of sterilization • E.g. Wet heating at 121°C for 15-20 minutes § Sterilized food products are shelf stable for > 6 months 33 Heat treatment – 2. Sterilization • Commercial sterilization § Combine heat and vacuum seal to destroy all spoilage and pathogenic microorganisms § Kill endospores of Clostridium botulinum § A treatment used to produce canned food • Canning (or called retort processing) § Food is filled into the containers (e.g. metal cans) § Heat sealed cans to destroy bacteria and spores 34 Heat treatment – 2. Sterilization • Canning § Commercial sterilization of low acid foods • Heating the product at 121°C for a duration • Sufficient to inactivate Clostridium botulinum spores by 12 log § Commercial sterilization of high acid foods • Heating the product at ~ 100°C • To destroy both vegetative cells and spores of spoilage microorganisms (particularly fungal spores) 35 Heat treatment – 2. Sterilization • One log reduction = 90% reduction or 10-fold reduction • 12 log reduction = 12 cycles of log reduction Number of microorganisms Log of microbial population Log reduction (from original) 1,000,000 106 0 100,000 105 1 10,000 104 2 1,000 103 3 100 102 4 10 101 5 1 100 6 0.1 10-1 7 0.01 10-2 8 0.001 10-3 9 0.0001 10-4 10 0.00001 10-5 11 0.000001 10-6 12 36 Heat treatment – Thermal destruction of microorganism • Bacterial populations killed by heat or chemicals tend to die at constant rates § E.g. 90% every minute • Microbial Death rate curve, plotted logarithmically (log), shows this constant death as a straight line E.g. If heating causes 90% death rate per minute, it means • 90% of microorganism is destroyed in the 1st min of heating • 90% of the remaining population is destroyed in the 2nd min of heating and so on 39 Heat treatment – Thermal destruction kinetics • Three important values used to measure the thermal-killing efficiency § D value § Z value § F value 40 Heat treatment – Thermal destruction kinetics • D value (decimal reduction time) § The time needed to reduce the number of a given microorganism by 90% (or 1 log cycle) at a specific temperature Microbial Death Rate Curve 41 Heat treatment – Thermal destruction kinetics • D value (decimal reduction time) § related to the temperature used in the process • D value decreases as the temperature increases § related to the heat resistance of microorganism • D values differ for different microbial species • Higher D value indicates greater heat resistance 43 Heat treatment – Thermal destruction kinetics • D values (decimal reduction time) § How to express D value ? • Always express D value with a thermal value (i.e. processing temperature) • Give the temperature as a subscript to the D • E.g. D121 = Time required to kill 90% of bacterial population at 121˚C Q: If microorganism A population is reduced by 90% after exposure to temperatures of 150˚C for 2 minutes, what is its D value? 45 Heat treatment – Thermal destruction kinetics • D-value can be estimated from the Death Rate Curve Heat treatment – Thermal destruction kinetics Q: What is the D100 for microorganism C? No. of surviving microorganism C Death rate curve of microorganism C at 100oC 10000 1000 100 10 1 0 2 4 6 8 10 Time (mins) 12 14 16 18 48 Heat treatment – Thermal destruction kinetics • Z value § The increase in temperature required to reduce D value by ten-fold (or 90%) § It can be obtained from a Thermal Death Time (TDT) curve • Plot the logarithms of D-values (heating time) against temperature 50 Heat treatment – Thermal destruction kinetics • Z-value can be estimated from the Thermal Death Time (TDT) curve • E.g. Z value = 10˚C à 10˚C increases in temperature (e.g. from 105 ˚C to 115 ˚C) can reduce the D value by 90% (e.g. from 100 minutes to 10 minutes) 51 Heat treatment – Thermal destruction kinetics Q: What is the Z value for heated Bacillus spores? Thermal Death Time curve of heated Bacillus spores Log of D-value (min) 1000 100 10 1 80 82 84 86 88 90 92 94 Temperature (℃) 96 98 100 102 104 52 Heat treatment – Thermal destruction kinetics • Z value - Implication of TDT curve § Time – temperature combination is important for killing microorganism • The higher the temperature used, the shorter the killing time is § D105 = 100 minutes and D115 = 10 minutes § 100 minutes at 105˚C has the same lethal effect as 10 minutes at 115˚C At 105 ˚C, D value = 100min à Using 100min to kill 90% of microbes At 115 ˚C, D value = 10min à Using 10min to kill 90% of microbes 54 Heat treatment – Thermal destruction kinetics 55 Heat treatment – Thermal destruction kinetics • F value (thermal death time) § The time in minutes required at a given temperature to reduce the microbial population to desired sterility level § F value can be estimated from Death Rate Curve T = temperature for sterilization Sterility level 57 Low temperature • Refrigeration (or called Chilling) § Holding food below ambient temperature and above freezing (2-8˚C) § Retard the growth and metabolic activity of most food microorganisms § Psychrophiles can grow • E.g. Pseudomonas spp., Listeria monocytogenes • Freezing § Temperature ≤ -18°C § Stop the growth and metabolic activity of most food microorganisms § Water unavailable due to ice formation § Cell injury 59 Dehydration • Removal of water from food • Inhibit microbial growth by decreasing water activity • Methods § Conventional drying (heat-induced) • Water removal by evaporation § Freeze-drying • Water removal by sublimation • Retain the food shape, color, and nutrients 60 Dehydration • Freeze-drying • Freeze and dehydrate of frozen food (under vacuum state) 61 Modified atmosphere packaging (MAP) • Altered gaseous environment applied to food enclosed in a gas barrier material § Combinations of carbon dioxide, nitrogen, and oxygen • Inhibit aerobes and delay growth of facultative anaerobes § E.g. Pseudomonas, Acinetobacter, and Moraxella • Retain the moisture content and freshness of food • Preservation of fruits, meat, poultry, and vegetables § Often in conjunction with refrigerated storage 62 Radiation • Various forms of radiation are used in the preservation of foods by destruction of microorganisms or inhibition of biochemical changes • They include α, β, γ, X-ray, free electron, etc. • The reactive ions produced by irradiation can destroy the microorganisms through: § changing the structure of cell membrane § affecting metabolic enzyme activity § affect DNA or RNA in cell-nuclei • Irradiated food does not become radioactive • Poultry, red meats, flour, spices, potatoes, fruits, vegetables, grains can be irradiated 63 Filtration • Membrane filtration § To remove undesirable solids and microorganisms from liquid foods by using a porous membrane / filter § E.g. Water, wine, beer, juice, soft drinks 64 B. Chemical methods of food preservation 65 Addition of acids • Pickling § Increase acidity of foods i. ii. Non-fermented pickling - Immersion of food in vinegar Fermented pickling - Natural anaerobic fermentation in brine (salt solution) • Produce lactic acid to increase acidity § Inhibit the growth of microorganism § The resulting food is called a pickle, made from a mixture of vegetable and fruit 66 Addition of salt • Curing § Or called Salting / Salt curing § Addition of salt (sodium chloride) or salt solution § Inhibit microbial growth • Dehydration § Draw out water from food by osmosis • Decrease water activity § High concentration of salt binds to water in food making it unavailable to microorganisms § E.g. meat and fish 67 Addition of sugar • Preservation of fruits with sugar • This sugar can be solid form, or high sugar density liquid such as honey, syrup • Inhibit microbial growth § Dehydration (by osmosis) § Decrease water activity • E.g. jams, jellies, and canned fruits 68 Other food preservatives • Antimicrobial food additives § Chemical compounds added to foods § Inhibit the growth of microorganism § Chemical antimicrobial agents • Not “natural” • Controversial § E.g. nitrate (NO3-) and nitrite (NO2-) in cured meat • A main ingredient in curing salt • It gives a desirable pink color to meat and inhibits the growth of microorganisms • Formation of nitrosamine à carcinogenic 69 Other food preservatives 70 C. Biological methods of food preservation 72 Fermentation • Fermentation is an incomplete oxidation of sugars initiated by microorganisms in the anaerobic condition producing lactic acid, carbon dioxide and ethanol • Fermentation by lactic acid bacteria § Production of organic acids • Lower the pH which inhibits the growth of undesirable microorganisms § Production of bacteriocins • Inhibit the growth of some microorganisms § E.g. Nisin – against Gram positive bacteria 73 Self-check exercises 1. What are the purposes of food preservation? 2. Give two principles of food preservation. 3. What is the similarity and difference between pasteurization and sterilization? 4. Z value is derived from thermal death time curve / death rate curve (Circle the correct answer) 5. What is curing? How does curing preserve the meat? 74 Self-check exercises 6. State True or False for the following statements regarding the D value of microorganism C. § The D100 of microorganism C is constant if the heating temperature is unchanged. § If the heating temperature is increased, the D value of microorganism C will be reduced. § D value is the time required to reduce 10% of microorganism. 75