There are three types of microorganisms that cause foodspoilage -- yeasts, moulds and bacteria growth 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 asfermentation False 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
•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
Fungal Spoilage Storage rot in grapes caused by Botrytis cinerea. Storage rot in strawberry caused by Botrytis cinerea. Blue mould rot in tomato caused by Penicilliumi spp. (also by Fusarium spp.) Black mummy rot of grapes caused by Guignardia bidwellii Watery soft rot in apple caused by Sclerotinia sclerotiorum. Blue mould on oranges caused by Penicillium digitatum.
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: sporeforming and nonspore-forming Bacteria 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 pressure Soft rot in tomatocanner caused by ErwiniaTemperatures higher than C[ F] can be carotovoraobtained only by pressure canning•Eatting spoiled food caused by bacteria cancause food poisoning
Microorganisms involved in food spoilage(Other than Canned Foods) with some examples of causative organisms Food Type of Spoilage Microorganisms involved Rhizopus nigricans Mouldy Penicillium Bread Aspergillus niger Ropy Bacillus subtilis Ropy Enterobacter aerogenes Saccharomyces Yeasty Zygosaccharomyces Maple sap and syrup Pink Micrococcus roseus Aspergillus Mouldy Penicillium Rhizopus Soft rot ErwiniaFresh fruits and vegetables Gray mold rot Botrytis Black mold rot A. niger Pickles, sauerkraut Film yeasts, pink yeasts Rhodotorula Alcaligenes Clostridium Fresh meat Putrefaction Proteus vulgaris Pseudomonas fluorescens Aspergillus Mouldy Rhizopus Penicillium Cured meat Pseudomonas Souring Micrococcus Lactobacillus Greening, slime Leuconostoc Discoloration Pseudomonas Fish Alcaligenes Putrefaction Flavobacterium Green rot P. fluorescens Pseudomonas Eggs Colorless rots Alcaligenes Black rots Proteus LactobacillusConcentrated orange juice "Off" flavor Leuconostoc Acetobacter Pseudomonas Poultry Slime, odor Alcaligenes
Enzymes are proteins found in all plants andanimals. If uncooked foods are not used whilefresh, enzymes cause undesirable changes incolour, texture and flavour. Enzymes aredestroyed easily by heat processingAtmospheric oxygen can react with some foodcomponents which may cause rancidity orcolor changes
Infestations (invasions) by insects androdents, which account for huge lossesin food stocks.Low temperature injury - the internalstructures of the food are damaged byvery low temperature.