Lecture 3 - Water

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University of Toronto St. George
Nutritional Science
Debbie Gurfinkel

NFS386 Lecture 327 Sept 2011Demineralization as you move down the ore size decreases to filter smaller and smallerFreeze concentration thingssmall ice crystals act as solutes at low concentrationslow coolingsolutes squeezed into tiny spacehighestAre there bacteria in bottled water concentration yesfast coolingsolutes pushed into unfrozen and small volumeunsafe to reuse bottles because bacterial contamination can occur if not food has unfrozen zones because of freezing point depressionproperly cleanedchemical reactions take place in unfrozen areas of foodoff flavoursindustrial freezingsmaller ice crystals quick freezing Extracellular water freezes first via osmosis large crystals slow rate of freezing with high concentrationmore osmosisand shrinking of cellsmall crystals fast rate of freezing has less shrinkage because cells are freezing quickly and concentration inside is not as high as it is outsideeither way ECF freezes first and ECF has more water in itdrip loss and thawingrunoff of water in foodwater in the ECF drains out faster when its melting How do you properly freeze apples at home Cut into thin slices for freezing issuesblanch before freezing avoid browningSlide 16browning reaction for thawed apple is because osmosis from slide 14 damages cellsSlide 17centre of apple has the most browning least freezing ice outside but freeze concentrated in the coreSlide 18 thawed apple drip loss water out of ICF Freezing promotes two opposing forces frozen food sill has a shelf life because of the unfrozen zones Why is it inadvisable to freeze food bacterial hazarddormant bacteria can grow out during thawthawing drip lossrefreezerubbery texture Freezer burn sublimation of icewater vapourdarkened spots on meat are dry regions Water activity beef jerky beef corn syrup solids sugar dextrose
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