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HNSC 1200 (46)
Snehil Dua (46)
Chapter 2

HNSC 1200 Chapter 2: Topic 2.7

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University of Manitoba
Human Nutritional Sciences
HNSC 1200
Snehil Dua

OS98 thin layer of the food product on the heated drum dries very quickly into thin layers. These layers are further ground to obtain powders. This method is not typically used for milk b/c the solubility of milk powder tends to be low if drum dried. freeze-drying: food is first frozen, then is placed in a vacuum where the ice is evaporated via sublimation (passes directly from a solid to a vapour w/o passing through liquid state). This is the most effective method of drying food b/c food is not exposed to high heat and therefore more vitamins remain intact. The food also retains its original shape. However, this method of drying is also more expensive. Problem with heat drying: • a problem with drying by heat is the loss of food’s heat-sensitive nutrients such as vitamin C, riboflavin and niacin. Heat can also alter the foods flavour, colour and structure. Pretreatments: some foods need to be pretreated before drying. 1. Physical: some fruits, such as pumps have their skin exposed to lye or hot water to crack the skin before drying. This shortens the drying time and improves the texture of the end product (in the case of plums, the prune). 2. Blanching: some fruits and vegetables (e.g.: carrots and potatoes) are blanched prior to drying to deactivate enzymes that cause browning. 3. Chemical: some vegetables and fruits (e.g. apricots and bananas) are dipped in sulphate solution or exposed to sulfur dioxide gas prior to drying to prevent browning and to protect against the loss of vitamins A and C. However, these products destroy thiamin and can cause allergic reactions in some people. 2. THERMAL PROCESSING the important heat treatment methods used in processing include sterilization, pasteurization, blanching and canning. Thermal processing can cause a loss of heat-sensitive nutrients. sterilization: Oc78 complete destruction of microorganisms through exte
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