food spoilage

Category: Education

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Food Spoilage Prepared by محمد عدنان القزاز Supervisor عبد الرؤوف المناعمة

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Food spoilage : means the original nutritional value, texture, flavor of the food are damaged, the food become harmful to people and unsuitable to eat. : Food poisoning ( or food borne illness) is an illness that you may get after eating food contaminated by certain bacteria, parasites, viruses, or chemicals.

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Conditions for Spoilage : Water pH Physical structure Temperature

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Intrinsic Factors : Composition pH presence and availability of water physical structure presence of antimicrobial substances

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Composition and pH pH impacts make up of microbial community and therefore types of chemical reactions that occur when microbes grow in food

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Water availability in general, lower water activity inhibits microbial growth water activity lowered by: Drying Addition of salt or sugar osmophilic microorganisms prefer high osmotic pressure xerophilic microorganisms prefer low water activity

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Physical structure grinding and mixing increase surface area and distribute microbes promotes microbial growth outer skin of vegetables and fruits slows microbial growth

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Antimicrobial substances coumarins – fruits and vegetables lysozyme – cow’s milk and eggs aldehydic and phenolic compounds – herbs and spices allicin – garlic polyphenols – green and black teas

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Extrinsic Factors Temperature : lower temperatures retard microbial Growth relative humidity : higher levels promote microbial growth Atmosphere : oxygen promotes growth modified atmosphere packaging (MAP) use of shrink wrap and vacuum technologies to package food in controlled atmospheres

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Microbial Growth and Food Spoilage food spoilage results from growth of microbes in food alters food visibly and in other ways, rendering it unsuitable for consumption different foods undergo different types of spoilage processes toxins are sometimes produced algal toxins may contaminate shellfish and finfish

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M icrobial spoilage : There are three types of microorganisms that cause food spoilage -- yeasts, moulds and bacteria. Yeasts growth causes fermentation which is the result of yeast metabolism. There are two types of yeasts true yeast and false yeast. True yeast metabolizes sugar producing alcohol and carbon dioxide gas. This is known as fermentation. False yeast grows as a dry film on a food surface, such as on pickle brine. False yeast occurs in foods that have a high sugar or high acid environment.

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Moulds grow in filaments forming a tough mass which is visible as `mould growth'. Moulds form spores which, when dry, float through the air to find suitable conditions where they can start the growth cycle again. Mould can cause illness, especially if the person is allergic to molds. Usually though, the main symptoms from eating mouldy food will be nausea or vomiting from the bad taste and smell of the mouldy food. Both yeasts and moulds can thrive in high acid foods like fruit, tomatoes, jams, jellies and pickles. Both are easily destroyed by heat. Processing high acid foods at a temperature of 100°C (212°F) in a boiling water canner for the appropriate length of time destroys yeasts and moulds.

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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 .

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Bacteria are round, rod or spiral shaped microorganisms. Bacteria may grow under a wide variety of conditions. There are many types of bacteria that cause spoilage. They can be divided into: sporeforming and nonspore-forming . Bacteria generally prefer low acid foods like vegetables and meat. In order to destroy bacteria spores in a relatively short period of time, low acid foods must be processed for the appropriate length of time at 116°C (240°F) in a pressure canner. Temperatures higher than 100°C [212°F] can be obtained only by pressure canning Eatting spoiled food caused by bacteria can cause food poisoning . Soft rot in tomato caused by Erwinia carotovora

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Microorganisms involved in food spoilage(Other than Canned Foods) with some examples of causative organisms Food Type of Spoilage Microorganisms involved Bread Mouldy Rhizopus nigricans Penicillium Aspergillus niger Ropy Bacillus subtilis Maple sap and syrup Ropy Enterobacter aerogenes Yeasty Saccharomyces Zygosaccharomyces Pink Micrococcus roseus Mouldy Aspergillus Penicillium Fresh fruits and vegetables Soft rot Rhizopus Erwinia Gray mold rot Botrytis Black mold rot A. niger Pickles, sauerkraut Film yeasts, pink yeasts Rhodotorula Fresh meat Putrefaction Alcaligenes Clostridium Proteus vulgaris Pseudomonas fluorescens Cured meat Mouldy Aspergillus Rhizopus Penicillium Souring Pseudomonas Micrococcus Greening, slime Lactobacillus Leuconostoc Fish Discoloration Pseudomonas Putrefaction Alcaligenes Flavobacterium Eggs Green rot P. fluorescens Colorless rots Pseudomonas Alcaligenes Black rots Proteus Concentrated orange juice "Off" flavor Lactobacillus Leuconostoc Acetobacter Poultry Slime, odor Pseudomonas Alcaligenes

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Diseases of spoiled food two primary types food-borne infections food intoxications

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Food-Borne Intoxications ingestion of toxins in foods in which microbes have grown include staphylococcal food poisoning, botulism, Clostridium perfringens food poisoning, and Bacillus cereus food poisoning

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Toxins ergotism toxic condition caused by growth of a fungus in grains aflatoxins carcinogens produced in fungus-infected grains and nut products fumonisins carcinogens produced in fungus-infected corn

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Enzymes Enzymes are proteins found in all plants and animals. If uncooked foods are not used while fresh, enzymes cause undesirable changes in colour, texture and flavour. Enzymes are destroyed easily by heat processing. Oxidation by air Atmospheric oxygen can react with some food components which may cause rancidity or color changes.

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Other factors Infestations (invasions) by insects and rodents, which account for huge losses in food stocks. Low temperature injury - the internal structures of the food are damaged by very low temperature.

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Controlling Food Spoilage

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Removal of Microorganisms usually achieved by filtration commonly used for water, beer, wine, juices, soft drinks, and other liquids

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Low Temperature refrigeration at 5 °C retards but does not stop microbial growth psychrophiles and psychrotrophs can still cause spoilage growth at temperatures below -10 °C has been observed

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High Temperature Canning Pasteurization

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Canning food heated in special containers (retorts) to 115 °C for 25 to 100 minutes kills spoilage microbes, but not necessarily all microbes in food

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Pasteurization kills pathogens and substantially reduces number of spoilage organisms different pasteurization procedures heat for different lengths of time shorter heating times result in improved flavor

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Radiation ultraviolet (UV) radiation used for surfaces of food-handling equipment does not penetrate foods Gamma radiation use of ionizing radiation (gamma radiation) to extend shelf life or sterilize meat, seafoods , fruits, and vegetables

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Detection of Food-Borne Pathogens must be rapid and sensitive methods include: culture techniques – may be too slow immunological techniques - very sensitive molecular techniques probes used to detect specific DNA or RNA sensitive and specific

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