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Lecture 4 - © E.Garcia 2010 FST 1 – Main topics –...

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Unformatted text preview: © E.Garcia 2010 FST 1 – Main topics – Lecture 04 Food and Energy Simple sugars relative to total sugars (%) Humans are heterotrophs: organisms that obtain energy from foods. In contrast, plants are autotrophs. The energy our body needs comes from carbohydrates, lipids and proteins. Apples Banana Glucose Grapes Carbohydrates The most abundant organic compounds on Earth Major source of energy for the body Have important functions in foods, such as ‐ sweetening ‐ thickening and gel formation ‐ precursors of flavor and color compounds Carbohydrates are classified as: ‐ Simple Sugars (mono‐ and disaccharides) ‐ Complex carbohydrates Monosaccharides are the simplest carbohydrates. Chemically, they are polyhydroxy aldehydes (ex.: glucose) and polyhydroxy ketones (ex.: fructose) Glucose and Fructose are 6‐carbon sugars with the same chemical formula: C6H12O6 There are monosaccharides with a backbone of 3 to 8 carbon atoms. The most common monosaccharides in foods are glucose, fructose and galactose; all are 6‐carbon sugars. Disaccharides are formed by 2 units of monosaccharides joined together by a GLYCOSIDIC bond. Examples: sucrose (table sugar) and lactose (milk sugar). Sucrose = Glucose−Fructose Lactose = Glucose−Galactose Glycosidic bond: linkage between 2 monosaccharide units. Note: The suffix “ose” is commonly given to carbohydrates. Fructose Carrot Tomato Sucrose Onions Others 0 50 100 Oligosaccharides are carbohydrates containing from 3 to 10 sugar units. Ex.: Raffinose, a trisaccharide Stachyose, a tetrasaccharide and Verbascose, a pentasaccharide o Polysaccharides contain > 10 sugar units up to thousands Ex.: Starch ‐ a common energy reserve of plants Cellulose ‐ structural component of plant cell walls Pectin ‐ component of plant cell walls and between cells, binding cells together Alginates ‐ seaweed polysaccharides; main source is the giant kelp Starch is a polymer formed by glucose units. It consists of two types of chain: amylose (linear chain) and amylopectin (branched chain). Both occur together in starch granules. Starch is abundant is seeds, roots, and tubers. Starch is digested by humans and supplies 4 kcal/g. Cellulose is also a polymer formed by glucose units, but composed only of linear chains. Cellulose cannot be digested by humans. It is a component of the dietary FIBER. Pectins form gels in food products such as jams, jellies, preserves. Alginates are used as food additives, frequently for their gel‐forming properties. Pectins and alginates cannot be digested by humans. Readings 1. McGee p.803‐805 (Carbohydrates) 2. McGee p.652‐655 (The Nature of Sugars) 3. McGee p. 282 (Figure) and p.283 (Starchy Vegetables) 4. McGee p. 258 (Fiber) ...
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