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-Even more tolerant of low pH and water activityViruses- (pseudo-organisms)can be agents of food brings disease but don’t cause food spoilage. They are not used to produce fermented foods.Function:Good,bad,ugly.Temperature requirement:Psychrophiles低,Psychrotrophs耐冷, Mesophiles温,Thermophiles热.Oxygen Requirement:Aerobic有氧,Anaerobic无氧,Facultative anaerobe都行Enzymatic deterioration: polyphenol+o2 (polyphenol oxidase)-> brown pigments-Can food may spoil by Maillard browning(chemical reaction)-slow at ambient temperatureFood Perservation:minimize deterioration, prevent microbiological harm to consumer, maintain quality and nutritional value.Thermal processing:1.Blanching:(Boiling water or steam for a short time, vege and fruit)Purpose:-Inactivate the enzymes-wlit vegetables-Drive off oxygen and other gases Can followwith freezing,dehydration,canning.2.Pasteurization:(temp 72°C for 15 secs) HTST(High temperature short time).use on milk and juice.Purpose:- destroy disease causing microorganism-Reduce the microbial load to a safe level(Low acid food: pathogens,Acid food:Spoilage microbes)-Putrefaction腐败 microorganism survive (Proteolytic and lipolytic spoilage(via enzymes)) cause off-flavours(solution: refeigeration3.Commercial sterilization (Botilinum cook):(121°C for 15 mins)Purpose: Destroys all viable disease causing and most spoilage causing microorganism,some not harmful thermophilic spores may survivem.Store 2years or more at room temperature.Clostridium botulinum is killed:-extremely heat resistant spores-produce deadly neurotoxin (blurred vision, difficulty breathing and swallowing, respiratory paralysis and death)-anaerobic 无氧- cannot grow well at pH of 4.6 or less.3.5.Ultra High Temperature(UHT)+ Aseptic Packaging:(140-150°C for 4-6seconds with Tetra Pak)-Food is packaged in pre-sterilized containers in a sterile environment. Purpose:shorter processing times,higher quality.store >6 months at room temp. Thermal Death Curves(TDC): Microorganisms are not killed instantaneously-Microbial death-logarithmic order of death. Under constant thermal conditions the same % of microbial population will be destroyed in a given time interval.Commercial sterilization(CS): Survivor Curve or Thermal Death Rate Curves(TDRC)A given temp.kills 90% microbial population in the1stminutes and the 90% of the remaining in the 2ndmins. D-value(time):time at a certain temp to kill 90% of the population.Z-value(°C):Temp change causes a 1log cycle change in theD-Value. (increase by a Z value temp,,D value decrease by 1 log(from 10 to 1) 反之亦然) F-value(min):Time required to kill MOs at 121°C.(Lethality of heat treatment)Margin of Safety(MS):minimize the survivors of C.botulium spores1.Low acid food-F value = 12D thermal process 2.Acid foods-F value=5D (C will not grow in <4.6pH)Thermal death Rate Curve(TDRC).