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Food spoilage



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  • 1. Gunjan Mehta,Lecturer,Shree M. & N. Virani Science College,Rajkot
  • 2. There are three types of microorganisms that cause foodspoilage -- yeasts, moulds and bacteriagrowth causes fermentation which is theresult of yeast metabolism. There are two types ofyeasts true yeast and false yeastTrue yeast metabolizes sugar producing alcoholand carbon dioxide gas. This is known asfermentationFalse yeast grows as a dry film on a food surface,such as on pickle brine. False yeast occurs in foodsthat have a high sugar or high acid environment
  • 3. •grow in filaments forming a tough mass which is visible as`mould growth. Moulds form spores which, when dry, floatthrough the air to find suitable conditions where they canstart the growth cycle again•Mould can cause illness, especially if the person is allergic tomolds. Usually though, the main symptoms from eatingmouldy food will be nausea or vomiting from the bad tasteand smell of the mouldy food•Both yeasts and moulds can thrive in high acid foods likefruit, tomatoes, jams, jellies and pickles. Both are easilydestroyed by heat. Processing high acid foods at atemperature of C ( F) in a boiling water canner forthe appropriate length of time destroys yeasts and moulds
  • 4. Fungal SpoilageStorage rot in grapes caused by Botrytiscinerea.Storage rot in strawberry causedby Botrytis cinerea.Blue mould rot in tomato causedby Penicilliumi spp. (also by Fusarium spp.)Black mummy rot of grapes causedby Guignardia bidwelliiWatery soft rot in apple causedby Sclerotinia sclerotiorum.Blue mould on oranges causedby Penicillium digitatum.
  • 5. are round, rod or spiral shapedmicroorganisms. Bacteria may grow under awide variety of conditions. There are manytypes of bacteria that cause spoilage. They canbe divided into: sporeformingand nonspore-formingBacteria generally prefer low acid foods likevegetables and meat. In order to destroy bacteriaspores in a relatively short period of time, lowacid foods must be processed for the appropriatelength of time at C ( F) in a pressurecannerTemperatures higher than C [ F] can beobtained only by pressure canning•Eatting spoiled food caused by bacteria cancause food poisoningSoft rot in tomatocaused by Erwiniacarotovora
  • 6. Microorganisms involved in food spoilage(Other than Canned Foods) with some examples of causative organismsFood Type of Spoilage Microorganisms involvedBreadMouldyRhizopus nigricansPenicilliumAspergillus nigerRopy Bacillus subtilisMaple sap and syrupRopy Enterobacter aerogenesYeastySaccharomycesZygosaccharomycesPink Micrococcus roseusMouldyAspergillusPenicilliumFresh fruits and vegetablesSoft rotRhizopusErwiniaGray mold rot BotrytisBlack mold rot A. nigerPickles, sauerkraut Film yeasts, pink yeasts RhodotorulaFresh meat PutrefactionAlcaligenesClostridiumProteus vulgarisPseudomonas fluorescensCured meatMouldyAspergillusRhizopusPenicilliumSouringPseudomonasMicrococcusGreening, slimeLactobacillusLeuconostocFishDiscoloration PseudomonasPutrefactionAlcaligenesFlavobacteriumEggsGreen rot P. fluorescensColorless rotsPseudomonasAlcaligenesBlack rots ProteusConcentrated orange juice "Off" flavorLactobacillusLeuconostocAcetobacterPoultry Slime, odorPseudomonasAlcaligenes
  • 7. Enzymes are proteins found in all plants andanimals. If uncooked foods are not usedwhile fresh, enzymes cause undesirablechanges in colour, texture and flavour.Enzymes are destroyed easily by heatprocessingAtmospheric oxygen can react with somefood components which may cause rancidityor color changes
  • 8. Infestations (invasions) by insectsand rodents, which account for hugelosses in food stocks.Low temperature injury - the internalstructures of the food are damagedby very low temperature.
  • 9. Removal ofMicroorganisms
  • 10.  Refrigeration at 5 C retards but does notstop microbial growth psychrophiles and psychrotrophs can stillcause spoilage growth at temperatures below -10 C has beenobserved