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1、,Food Microbiology,Lecture #9,Conditions for Spoilage,WaterpH Physical structureOxygentemperature,Microorganism Growth in Foods,Intrinsic Factors,compositionpHpresence and availability of wateroxidation-reduction potentialaltered by cookingphysical structurepresence of antimicrobial substances,Compo
2、sition and pH,putrefactionproteolysis and anaerobic breakdown of proteins, yielding foul-smelling amine compoundspH impacts make up of microbial community and therefore types of chemical reactions that occur when microbes grow in food,Water availability,in general, lower water activity inhibits micr
3、obial growthwater activity lowered by:dryingaddition of salt or sugarosmophilic microorganismsprefer high osmotic pressurexerophilic microorganismsprefer low water activity,Physical structure,grinding and mixing increase surface area and distribute microbespromotes microbial growthouter skin of vege
4、tables and fruits slows microbial growth,Antimicrobial substances,coumarins fruits and vegetableslysozyme cows milk and eggsaldehydic and phenolic compounds herbs and spicesallicin garlicpolyphenols green and black teas,Extrinsic Factors,temperaturelower temperatures retard microbial growthrelative
5、humidityhigher levels promote microbial growthatmosphereoxygen promotes growthmodified atmosphere packaging (MAP)use of shrink wrap and vacuum technologies to package food in controlled atmospheres,Microbial Growth and Food Spoilage,food spoilageresults from growth of microbes in foodalters food vis
6、ibly and in other ways, rendering it unsuitable for consumptioninvolves predictable succession of microbesdifferent foods undergo different types of spoilage processestoxins are sometimes producedalgal toxins may contaminate shellfish and finfish,Food Spoilage,Approximately 1/3rd of all food manufac
7、tured in world is lost to spoilageMicrobial content of foods (microbial load): qualitative (which bugs) and quantitative (how many bugs)Shelf lifeNon-perishable foods (pasta)Semiperishable foods (bread)Perishable foods (eggs),General Principles,Minimize contamination by:Good management processesAcce
8、ptable sanitary practicesRapid movement of food through processing plantWell-tested preservation procedures,Spoilage,MeatCutting board contaminationConveyor beltsTemperatureFailure to distribute quicklyFecal bacteria from intestinesFishPolluted watersTransportation boxes,Spoilage,Poultry and EggsHum
9、an contactPenetration by bacteriaMilk and Dairy ProductsLactobacillus and Streptococcus species that survive pasturization (sour milk)Breads Spores and fungi that survive bakingGrainsFungi produce toxins,Food-Borne Diseases,two primary typesfood-borne infectionsfood intoxications,Preventing Foodborn
10、e Disease,Food infections (microbes are transferred to consumer)Food poisoning (results from the toxin consumption),Food-Borne Intoxications,ingestion of toxins in foods in which microbes have growninclude staphylococcal food poisoning, botulism, Clostridium perfringens food poisoning, and Bacillus
11、cereus food poisoning,Toxins,ergotismtoxic condition caused by growth of a fungus in grainsaflatoxinscarcinogens produced in fungus-infected grains and nut productsfumonisinscarcinogens produced in fungus-infected corn,Controlling Food Spoilage,Removal of Microorganisms,usually achieved by filtratio
12、ncommonly used for water, beer, wine, juices, soft drinks, and other liquids,Low Temperature,refrigeration at 5C retards but does not stop microbial growthpsychrophiles and psychrotrophs can still cause spoilagegrowth at temperatures below -10C has been observed,High Temperature,canningpasteurizatio
13、n,Canning,food heated in special containers (retorts) to 115 C for 25 to 100 minuteskills spoilage microbes, but not necessarily all microbes in food,Spoilage of canned goods,spoilage prior to canningunderprocessingleakage of contaminated water into cans during cooling process,Pasteurization,kills p
14、athogens and substantially reduces number of spoilage organismsdifferent pasteurization procedures heat for different lengths of timeshorter heating times result in improved flavor,Water Availability,Chemical-Based Preservation,GRASchemical agents “generally recognized as safe”pH of food impacts eff
15、ectiveness of chemical preservative,Radiation,ultraviolet (UV) radiationused for surfaces of food-handling equipmentdoes not penetrate foodsGamma radiationuse of ionizing radiation (gamma radiation) to extend shelf life or sterilize meat, seafoods, fruits, and vegetables,Detection of Food-Borne Path
16、ogens,must be rapid and sensitivemethods include:culture techniques may be too slowimmunological techniques - very sensitivemolecular techniquesprobes used to detect specific DNA or RNAsensitive and specific,comparison of PCR andgrowth for detection of Salmonella,nucleic acid can be detectedeven whe
17、n plaque-formingability is lost,Surveillance for food-bornedisease,PulseNetestablished by Centers for Disease Controluses pulsed-field gel electrophoresis under carefully controlled and duplicated conditions to determine distinctive DNA pattern of each bacterial pathogenenables public health officials to link pathogens associated with disease outbreaks in different parts of the world to a specific food source,
