Penetrationcontact tv dinner patties pros rapid

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penetration/contact (TV dinner, patties) PROS: rapid process, almost no DH, O2 is excluded oxidative spoilage, individual freezing pcs have less freezing damage CONS:difficult to find suitable freezants, cost of operating is high. Packaging material for frozen foods:resistant to water vapor transfer: (food to the dry cold environment,freezer burn), does not shatter in cold temp, resists formation of pinholes, barrier to light and O2  slows/protects from chemical changes like photooxidation.Lesson 8:Process during dehydration (long storage life):1) as much water from food as possible is transferred to environ 2) heat is transferred to the food (promoting H2Oremoval) Principle:dehydrated foods have lower AW (0.2-0.6); not enough free H2O for MO growth (needs >0.93), staphylococcus aureus (pathogen; 0.85), mould (>0.6),chemical rxns (>0.3), chemical rxns *MOs not killed, resume growth after rehydration Concentration: only some of the H2O is removed from food  concentrate of foodconstituents; not fully shelf-stable so it requires other forms of preservation: refrig, dehy, thermal processing (eg. juice, canned soup, jams, maple syrup, evap & condmilk)Changes during Dehydration: 1) Shrinkage: H2O migrates out and evap; H2O soluble substances (sugars, acids, and salts) are carried out to surface of dehyfoods (contributes to poor rehydration) and food “shrinks2) Case Hardening: rapid drying causes compounds (eg. sugars) to form hard, fairly impermeable case aroundfood (contributes to higher rate of dehydration) 3) Chemical Changes: browning and flavour changes, Maillard browning as [solutes] , denaturation of protein,
aggregation of Polyssachairdes, loss of water binding capacity, loss of H2O soluble components, conc. of surface material, loss of volatiles (flavour compd) Factorsaffecting Dehydration: Surface Area (smaller = more rapid), temp of drying air(temp = rate), air velocity: maximize velocity of heated air moving around thefood particles, humidity of drying air(drier air absorbs more), atmos. pressure and vacuum(boiling point by temp) *4.5 lb grapes = 1 lb raisins Methods forDehydration: Sun Drying: (eg. Fruit/vegg, fish) GOOD - dry, warm climates, inexpensive BAD – slow, pests Spray Drying:(eg. powder skim, instant coffee/tea/eggs) liquidfoods and purees; tiny droplets of food sprayed into stream of hot air; rapid method Tray (Air) Drying: (eg pasta, F&V, spices, jerky) trays or racks; hot air @ set velocity;poor rehydration (case hardening); food shrinkage; dense product; quick and inexpensive Drum Drying: semisolid foods/food paste/purees; rotated heated drum  driedfood scraped off; rapid drying Freeze Drying:During freeze drying, water is removed from food in the frozen state without transition through the liquid state:called sublimation(eg. instant soups, high quality coffee, space food) food in frozen state; vacuum chamber; radiant heaters; water sublimes (solid  vapour); prevents heat

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