Transcript Chapter 41
Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Chapter 40 Microbiology of Food 1 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Microbial Growth and Food Spoilage • results from growth of microbes in food – alters food visibly and in other ways, rendering it unsuitable for consumption • involves predictable succession of microbes • different foods undergo different types of spoilage processes • toxins are sometimes produced 2 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Microbial Growth and Food Spoilage… • microbial growth is controlled by – intrinsic factors • factors related to the food itself – extrinsic factors • environment where food stored 3 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Figure 40.1 4 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Intrinsic Factors • food composition - carbohydrates – mold predominates • degrades food by hydrolysis, tomatoes particularly susceptible • little odor • ergotism – hallucinogenic alkaloids released by Claviceps purpurea – may cause death 5 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Table 40.1 6 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Figure 40.2 7 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Intrinsic Factors… • food composition – proteins or fats – bacterial growth predominates • putrefaction – proteolysis and anaerobic breakdown of proteins, yielding foul-smelling amine compounds • unpasteurized milk spoilage – acid production followed by putrification • butter – short chained fatty acid production results in rancid butter 8 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Figure 40.3 9 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Figure 40.4 10 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Intrinsic Factors… • pH – impacts make up of microbial community and therefore types of chemical reactions that occur when microbes grow in food – e.g., low pH favors yeast and mold • presence and availability of water – in general, lower water activity inhibits microbial growth 11 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Intrinsic Factors… • oxidation-reduction potential – altered by cooking – lower redox – more bacteria and anaerobes • physical structure – grinding and mixing distribute microbes; promotes microbial growth – outer skin of vegetables and fruits slows microbial growth 12 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Antimicrobial Substances • coumarins – fruits and vegetables • lysozyme – cow’s milk and eggs • aldehydic and phenolic compounds – herbs and spices • allicin – garlic • polyphenols – green and black teas 13 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Extrinsic Factors • temperature – lower temperatures retard microbial growth • relative humidity – higher levels promote microbial growth • atmosphere – oxygen promotes growth – modified atmosphere packaging (MAP) • use of shrink wrap and vacuum technologies to package food in controlled atmospheres 14 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Controlling Food Spoilage • modern era of food microbiology established by Louis Pasteur in 1857 • methods of preservation – goal is to eliminate or reduce the populations of spoilage and disease causing microbes while maintaining food quality 15 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Removal of Microorganisms • water, wine, beer, juices, soft drinks, and other liquids usually by filtration • may better preserve flavor and aroma 16 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 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 17 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. High Temperature: Canning • food heated in special containers (retorts) to 115°C for 25 to 100 minutes • kills spoilage microbes, but not necessarily all microbes in food • spoilage of canned foods – spoilage prior to canning – underprocessing – leakage of contaminated water into cans during cooling process 18 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Figure 40.5 19 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Pasteurization • kills pathogens and substantially reduces number of spoilage organisms • different pasteurization procedures heat for different lengths of time – shorter heating times result in improved flavor 20 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Water Availability • dehydration – e.g., lyophilization to produce freezedried foods is commonly used to eliminate bacterial growth – food preservation occurs as a result of free-water loss and an increase in solute concentration 21 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Table 40.2 22 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Chemical-Based Preservation • GRAS – chemical agents “generally recognized as safe” – agents include organic acids, sulfite, ethylene oxide gas, ethyl formate – sodium nitrite – inhibits spore formation in meats, forms nitrosamines • pH of food impacts effectiveness of chemical preservative 23 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Table 40.3 24 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Radiation • radappertization – use of ionizing radiation (gamma radiation) to extend shelf life or sterilize meat, seafoods, fruits, and vegetables – excellent penetrating power – food not radioactive – kills microbes in moist foods by producing peroxides from water • peroxides oxidize cellular constituents 25 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Radiation… • electron beams – electrons are electrically generated, so can be turned on only when needed – does not generate radioactive waste, but also does not penetrate foods as deeply as gamma radiation 26 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. 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 27 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Microbial Product-Based Inhibition • e.g., nisin from Lactococcus lactis – used in low-acid foods to inactivate Clostridium botulinum during canning process • e.g., bacteriophages that kill Listeria monocytogenes – sprayed onto ready-to-eat meats prior to packaging 28 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Packaging • modified atmosphere packaging (MAP) – gases in stored food affect microbial growth – shrink wrap materials and vacuum technology control atmosphere • impermeable to oxygen • superoxide radicals inhibit growth – polylactic acid • green alternative to plastic made from wood and corn • embedded with nisin which is slowly released 29 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Types of Food-Borne Disease • about 76 million cases/yr in U.S. – 18% attributed to known pathogens – at least 5,000 deaths/yr in U.S. • pathogens – Noroviruses, Campylobacter jejuni, Salmonella are major causes – E. coli and Listeria are also important pathogens 30 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Types of Food-Borne Disease… • two primary types – food-borne infections – food intoxications • transmission – breakdown in hygiene – fecal-oral route key – fomites also important 31 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Food-Borne Infection • ingestion of pathogen, followed by growth, tissue invasion, and/or release of toxins • raw foods (e.g., sprouts, raspberries, and seafood) are important sources 32 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Table 40.4 33 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Food-Borne Infections… • Listeriosis – pregnant women, the young and old, and immunocompromised individuals most vulnerable – responsible for the largest meat recall in U.S. – at-risk people should not eat soft cheeses, refrigerated smoked meats, deli meats, and undercooked hot dogs 34 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Food-Borne Intoxications • ingestion of toxins in foods in which microbes have grown • produce symptoms shortly after the food is consumed because growth of the disease-causing microorganism is not required • include staphylococcal food poisoning, botulism, Clostridium perfringens food poisoning, and Bacillus cereus food poisoning 35 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Other Food Disease • enterohemorrhagic E. coli (O157:H7) – normal inhabitant of intestines of mammals including cattle, swine • contamination of meat during slaughter • in salad vegetables contaminated in field – shiga toxin from horizontal gene transfer from Shigella • may result in life-threatening hemolytic uremic syndrome, most common in children and elderly 36 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Other Food Disease • fungus-derived toxins – aflatoxins • carcinogens produced in fungus-infected grains and nut products – fumonisins • carcinogens produced in fungus-infected corn • algal toxins • contaminate fish and shellfish 37 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Figure 40.6 38 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Figure 40.7 39 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Detection of Food-Borne Pathogens • must be rapid, sensitive and simple and for prevention • methods include: – culture techniques – may be too slow but are most likely to detect food pathogens – immunological techniques - very sensitive – molecular techniques • probes used to detect specific DNA or RNA • sensitive and specific 40 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Detection of Food-Borne Pathogens… • PulseNet – established by Centers for Disease Control – uses pulsed-field gel electrophoresis under carefully controlled and duplicated conditions to determine distinctive DNA pattern of each bacterial pathogen – enables public health officials to link pathogens associated with disease outbreaks in different parts of the world to a specific food source 41 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Figure 40.8 42 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Detection of Food-Borne Pathogens… • in addition to PFGE, PCR and RFLP are increasingly developed and used – amplify small quantities – species specific – microarray techniques directly from food or water 43 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Figure 40.9 44 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Microbiology of Fermented Foods • chemical changes in food brought about microbial action • major fermentations used are lactic, propionic, and ethanolic fermentations 45 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Fermented Milks • majority of fermented milk products rely on lactic acid bacteria (LAB) belonging to the genera Lactobacillus, Lactococcus, Leuconostoc, and Streptococcus – gram-positives that tolerate acidic conditions, non-spore forming, aerotolerant with a strictly fermentative metabolism 46 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Figure 40.10 47 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Table 40.5 48 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Fermented Milks… • mesophilic – Lactobacillus and Lactococcus – buttermilk and sour cream • thermophilic – Lactobacillus and Streptococcus – yogurt • probiotics – Lactobacillus and Bifidobacterium – addition of microbes to the diet to improve health beyond basic nutritive value 49 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Probiotics and Standardization • probiotics – live microorganisms, which when administered in adequate amounts, confer a health benefit to the host – specific requirements should be met • microorganisms – Lactobacillus, Bifidobacterium 50 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Figure 40.11 51 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Benefits of Probiotics • • • • • immunomodulation control of diarrhea anticancer effects – colon cancer possible modulation of Crohn’s Disease treatment of enteric disease – competition with pathogens – antibiotic resistance is continually rising 52 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Benefits of Probiotics… • Lactobacillus acidophilus and Bifidobacterium – improve lactose intolerance – improves general intestinal health and balance – may lower serum cholesterol – may have anti-tumor activity 53 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Other Milk Fermentations • yeast lactic – yeasts, lactic acid bacteria, and acetic acid bacteria – kefir • mold lactic – filamentous fungi and lactic acid bacteria – villi 54 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Cheese Production • approximately 2,000 distinct varieties representing 20 general types • classified based on – texture, hardness (soft, semi-soft, hard, very hard) • all from lactic acid fermentation – molds may further enhance 55 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Cheese Production… milk lactic acid bacteria and rennin curd removal of whey ripening by microbial action cheese 56 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Table 40.6 57 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Figure 40.12 58 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Meat and Fish • • • • • • 59 sausages hams bologna salami izushi – fish, rice, and vegetables katsuobushi – tuna Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Wines and Champagnes • enology (wine production) – crushed grapes • separation and storage of liquid (must) before fermentation – fresh must • treated with sulfur dioxide fumigant • Saccharomyces cerevisiae or S. liposideus added for consistent results • fermented for 3–5 days at 20–28oC 60 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Figure 40.13 61 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Wines and Champagnes… • dry or sweet wines – controlled by regulating initial must sugar content • racking – removes sediment produced during fermentation 62 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Beers and Ales • cereal grains used for fermentation – malt • germinated barley grains having activated enzymes – mash • the malt after being mixed with water in order to hydrolyze starch to usable carbohydrates – mash heated with hops • hops provide flavor and assist in clarification of wort • heating inactivates hydrolytic enzymes 63 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Figure 40.14 64 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Beers and Ales… • wort inoculated (pitched) with desired yeast – bottom yeasts • used in production of beers – top yeasts • used in production of ales • freshly fermented beers are aged or lagered – CO2 usually added at bottling • beer can be pasteurized or sterilized by filtration 65 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Figure 40.15 66 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Distilled Spirits • similar to beer-making process – begins with sour mash • mash inoculated with homolactic bacterium – following fermentation, is distilled to concentrate alcohol 67 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Production of Breads • involves growth of Saccharomyces cerevisiae (baker’s yeast) under aerobic conditions – maximizes CO2 production, which leavens bread • other microbes used to make special breads (e.g., sourdough bread) • can be spoiled by Bacillus species that produce ropiness 68 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Other Fermented Foods… • sufu – from fermentation of tofu • sauerkraut (sour cabbage) – from wilted, shredded cabbage • pickles – from cucumbers • silage – from grass, chopped corn, and other fresh animal feeds 69 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Table 40.7 70 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Microorganisms as Foods and Food Amendments • mushrooms (e.g., Agaricus bisporus) • cyanobacterium Spirulina dried cakes • probiotics – Lactobacillus acidophilus in beef cattle • decrease E. coli O157:H7 – Bacillus subtilis (PREEMPT) in poultry • limit colonization of gut by the process of competitive exclusion • reduces Salmonella and Campylobacter 71 Copyright © The McGraw-Hill Companies. Permission required for reproduction or display. Figure 40.16 72