Even more tolerant of low ph and water

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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 ,Psychrotrophs 耐冷 , Mesophiles ,Thermophiles . 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 temperature Food 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 follow with 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: refeigeration 3.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 2 years 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 the 1 st minutes and the 90% of the remaining in the 2 nd mins. 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 the D-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).

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