Microbes and Food 3 17 14 Food contamination Food contamination with microbes does not always result in spoilage disease Microbes Play important role in food production Primarily via fermentation reactions Fermentation Incomplete breakdown of carbs when oxygen is not present Pyruvic acid Plays central role Microbes produce enzymes of fermentation Microbial enzymes convert pyruvic acid to useful products secreted from cell Controlled food spoilage Culture specific Alcohols acids other by products give foods their unique qualities such as taste aroma texture Ex butter is composed of diacetyl and butryic acid Ex Swiss cheese is made of propionic acid By products also act as preservatives acids to prevent growth of dangerous and food spoilage microbes Wine Fermented fruit juice Any fruit can be source Most common microbe used is the budding yeast Saccharomyces Often yeast cells are derived directly from the fruit alternatively added from pure cultures Fruit juice provides nutrients for growth of yeast very rich in Growth initially by aerobic respiration CO2 produced from carbs Krebs Cycle As CO2 accumulates anaerobic environment results and fermentation begins Wine II Prolonged exposure to oxygen Harmful to wine making During fermentation pyruvic acid from glycolysis is not directed to Krebs Cycle instead converted to ethyl alcohol When alcohol content reaches about 12 the yeast dies Different varieties of wine depends on the Source of the grapes Strains of fermentation microbes Presence absence of stems and skin in crushed juice during fermentation distinguishes whether the wine will be red or wine Cheese Product of microbial fermentation of milk Primarily effect on casein the milk protein Type of cheese results from Microbe used in fermentation Source of milk etc Bread growth texture Flour mostly from wheat used as an energy source for yeast Flour protein known as GLUTEN gives bread its spongy Kneading introduces crosslinks between gluten molecules Yeast sends pyruvic acid to both Krebs Cycle hence CO2 production which causes bread to rise and fermentation ethanol produced is vaporized during baking Sour dough bread involves the use of lactobacillus to produce lactic acid and other Other foods Soy sauce Beer Fermentation of soybeans Fungus Aspergillus Fermentation of grain barley rice rye Saccharomyces species Sake from rice Technically a beer rather than wine Aspergillus used for fermentation Cocoa Coffee roasting Fermentation of pulp surrounding beans followed by drying or Competition between Microbes and Animals for Food 30 of food supply lost to spoilage Microbial contamination Foods contain nutrients and moisture to support microbial growth Result Uncontrolled fermentation Food with little moisture will not support microbial growth Dry foods keep well Role of Microbiologists in Food Industry Design protocols during preparation to prevent microbial contamination Detect contamination before consumption numbers and species Shelf life of food Depends on number of microbes initially present in food Potato chips dry pasta long shelf life Fish milk short shelf life Acceptable to have some microbes in certain foods Hamburger less than 1000 staph gram because it will be cooked Sliced ham Most common source of staph food poisoning because staph are salt tolerant Spoilage DOES NOT always result in sickness Food decomposes and is not palatable Microbial load of some food products is very HIGH Yogurt and pickles Not harmful but actually beneficial Even pasteurized milk has a high microbial load Source of microbes that contaminate food 1 Air 2 Soil 3 Animals 4 Human handling 5 Water used for cleaning or in the habitat ex fish Factors that influence microbial growth 1 Water content 2 ph Fungi are LOW ph tolerant acids 3 Structure of food product Ex steak vs hamburger 4 Oxygen 5 Temperature Consequences of microbial action on food Stench Caused by hydrogen sulfide Also due to CADAVERAE PUTRACINE Sour taste Caused by acid fermentation Gas production Bloating of cans killed animals Pigment production Red by Serratia Blue green by Pseudomonas Microbial action on food 3 19 14 Meats nutrients Very susceptible to spoilage because they are a good source of Cannot be pasteurized Many opportunities for contamination during processing Fecal bacteria Contaminated cutting utensils Exposure to moderate temperature Ex contaminated hamburger Sliminess and brownish color indicate spoilage before smell does Processed meats are especially susceptible due to frequent handling Fermented meats such as hard sausage are less susceptible Acidity inhibits growth of spoilage of microbes Fish Susceptible to spoilage even at low temperatures Microbes on fish are psychrophiles Filter feeders such as clams and mussels have a potentially high microbial load since they concentrate microbes in their systems TRIMETHYLAMINE Characteristic rotting fish smell Derived from metabolic activity of marine bacteria on fish muscle Mostly due to Salmonella contamination from GI tract of poultry Eggs Milk and Dairy Eggs Eggs exit from cloaca Some eggs now pasteurized Milk and dairy Very nutritious Casein protein Lactose carbohydrates Butterfat Milk is sterile within cow udder Contamination comes from soil microbes manure human handling etc Fermentation mainly by lactobacilli that survive pasteurization Leads to acidification that curd formation Food Preservation Heat Canning heat and exclusion of air is bases for success Heat results in denaturation of proteins and membranes Shelf life of canned food ranges from 1 5 years Potential danger botulism from spores of CLOSTRIDIUM BOTULINUM Grown in low oxygen environment Pasteurization Developed by Louis Pasteur initially for preservation of wine then other liquids milk beer etc in the late 1800 s Objective Eliminate pathogens and reduce microbial load to increase shelf life NOT a sterilization procedure since ALL microbes are not killed Organisms that survive pasteurization Endospore forming microbes Ex C BOTULINUM Thermoduric heat tolerant organisms Ex STREPTOCOCCI Thermophiles Methods of Pasteurization Tradition Flash Ultra 65 degrees Celsius for 30 minutes 72 degrees Celsius for 20 seconds Increases shelf life 2 3 wks 130 degrees Celsius for 3 seconds Increases shelf life up to 9 mo Typically refrigeration required after pasteurization Low temperature Reduces metabolic activity of microbes Growth rate dramatically reduced In many instances does not kill microbes However psychrotrophs