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level: 19B - Food Preservation by Drying

Questions and Answers List

level questions: 19B - Food Preservation by Drying

QuestionAnswer
Drying Objectivescan be used to retain the viability of starter culture bacteria for use in bioprocessing - prevent growth of vegetative cells - prevent germination and outgrowth of microbial spores - prevent toxin production by toxigenic molds and bacteria
Natural Dehydration- uncontrolled, slow process - water removed by heat of sun (solar drying) - low cost method - used for grains and some foods - spoilage and pathogenic bacteria/yeasts/molds can grow during the process
Mechanical dryingex: tunnel drying, roller drying, spray drying - controlled process - rapid; eliminates risk of microbial growth - foods dried within a few seconds to hours - liquids may be partially concentrated before drying - some microbes die during drying, some sub-lethally injured - spores generally survive
Freeze drying- acceptance quality of foods least affected: little/no effect on shape/size of food - relatively costly - foods rapidly frozen then exposed to high vacuum - water removed by sublimation, ice transformed directly to water vapor - some cells die, some sub-lethally injured - spores unaffected
Foam drying- vigorous whipping or injecting gas (air/nitrogen) in liquid food to produce foam, food usually concentrated prior to whipping - surface area increased - foam dried by warm air (50-80C) - some foods don't have foaming properties --> addition of foaming agents and foam stabilizers (ex. egg albumen, gelatin, carboxymethyl cellulose, maltodextrin - food to be foam dried should be of high microbial quality, process has little lethal effect on microbial cells and spores
Smoking- food product exposed to low heat and smoke - smoke deposited on surface during heating - many low-heat processed meat products produced this way (dry and semi-dry sausages and smoked fish) - some antimicrobials in smoke like phenolic compounds, carbonyls, and organic acids
Smoking antimicrobial components- phenols: disrupt bacterial membranes - carbonyls (ketones and aldehydes): sequester low MW nutrients - organic acids: inhibit microbial energy production
Intermediate moisture foods- foods with aw = 0.7-0.9, typ 10-40% MC - can be eaten without rehydration - shelf stable for relatively long periods without refrigeration - considered microbiologically safe --> water binding solutes and hydrophilic colloids added to bind water - microbes can survive but low aw prevents bacterial growth - yeasts and molds can grow --> preservatives added to control (potassium sorbet, sodium benzoate) - ex: jam/jelly, honey, candies, salami, baked foods, dried fruits, jerky