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HNSC 1200 (29)
Snehil Dua (29)
Lecture 20

HNSC 1200 Lecture 20: Unit 4

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Human Nutritional Sciences
HNSC 1200
Snehil Dua

HNSC 1200 Unit 4: The Chemistry of Foods: Water and Carbohydrates Water Learning Objectives:  Discuss the physical and chemical properties of water Differentiate between hard and soft water Identify chemicals that can be found in water Describe the functions of water in food and food preparation Course Notes: Introduction Water is the most indispensable of all nutrients The body needs more water each day than any other nutrient 50 times more water than protein and 5000 times more water than Vit. C Water is also the most abundant nutrient in many foods SEE FIGURE 1 The water content of foods can be impacted by food processing (e.g., a raw apple is about 84% water, while dried apple is about 32% water) Physical and Chemical Properties of Water Water is made up of two hydrogen atoms bonded with one oxygen atom (SEE FIGURE 2) Water freezes at 0C and will expand once frozen This is the cause of texture changes when produce is frozen Water boils at 100C at normal atmospheric pressure (near sea level) At high altitudes, the boiling point is lowered and it takes longer to cook foods Water activity (aw) is the amount of free (available) water in a food Water activity is different than the moisture content of foods SEE TABLE 1: Water Activity of Some Common Foods Foods with high water activity are at higher risk of microbial spoilage Water Hardness – the presence of mineral salts determines water hardness o Temporarily hard water – contains bicarbonate salts. It can be softened by boiling o Permanently hard water – contains calcium and magnesium sulfates It cannot be softened by boiling because the minerals are not precipitated by heat. It can be softened by exchanging sodium ions for the calcium and magnesium ions (results in very high levels of sodium) o Hardnes causes scale build up on equipment and pipes o Hard water is usually alkaline – can affect plant pigments when cooking vegetables (e.g., red cabbage can turn green when boiled in hard water) OSDP Chemicals Found in Water The chemicals that are found in water depend on the source Fluoride may be added. Fluoride is important in t
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