Air freezing still air freezers no circulation slow

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1.air-freezing: still air freezers (no circulation, slow freezing), air blast freezers (-18C-34C, cold air @high velocity with IQF-individually quick frozen; 2.indirect contactfreezing: scraped surface/slush freezers-helps incorporate air bubbles into the freezing mix; 3.immersion/cryogenic: immersion in refrigerant liquid; cryogenic-direct contact w/refrigerating medium, rapid freezing rates; packaging material for frozen foods:resistant to transfer of water vapour/freezer burn, barrier properties towards light&oxygen //// L8-Dehydration process:1.heat/energy transferred to the food (promotes water removal)-2.water transferred from food into dehydrating environment; (microbial growth=aw0.93)-(staphylococcusAureus=aw0.85)-(mould=0.60)-(below aw0.6, no microbial growth)-(chem.rxn=eg.maillard=aw¿0.3)-in dehydration, H20 physically removed to lower aw; DH foods have low water activity 0.2-0.6; dehydration:removal of as much h2o from food as possible, imparts long storage life; concentration:some of the h2o is removed from food; concentrates the food constituents; changes during dehydration: (shrinkage) h2o migrates from inside of food to surface where it evaporates-it carries with it h2o soluble substances dissolved; (case hardening) rapid drying causes compounds to form a hard case-can cause rate of dehydration to increase; (chemical changes) browning&flavor changes due to reactions-denaturation of proteins, aggregation of polysaccharides; factors affecting dehydration:1.surface area-smaller food,more rapid rate of moisture loss; 2.increase temp, increase dehydration rate; 3.maximize velocity of heated air moving around the food particles; 4.humidity-drier the air, more moisture it can absorb; 5.atmospheric pressure&vacuum-water boils at 100C, at lower pressure, boiling temp will decrease; //// drying dehydration methods:SUN-DRY:leaving food under sun, done only in dry, warm climates, long but inexpensive, susceptible to microbes, fruits; SPRAY-DRY:liquid foods/purees are sprayed into a stream of heated air, rapid rehydration,skim milk powder,high capital costs; TRAY(AIR)-DRY:food placed on trays/racks, medium hot air travelling a set velocity, quick and cheap, temp is important; DRUM-DRY: semi-solid foods thinly layered on heated rotating drum, mashed potatoes, products may get overcooked, not suitable for sugary foods; FREEZE-DRY:food placedin vacuum chamber with radiant heaters, sublimation occurs(water transitioning to vapor); excellent rehydration, very expensive, long duration, space food; VACUUM-MICROWAVE-DRY: lowers boiling point, quicker than freeze dry, expensive, high nutrient&flavor retention; DEEP-FAT-FRY:hot frying medium, food picks up oil, bakery products; EXTENSION-DRY: food slurries heated with steam under pressure, moist heat causes gelatinzation and cooking of product, snack foods; //// dehydrated foods are hygroscopic, packaging must prevent water vapor transmission;packaging must be durable //// L9biotechnology:application of science&engineering in direct or indirect use of living organisms or their parts in natural/modified

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