Lecture 5

Lecture 5 - © E.Garcia 2010 FST 1 – Main topics –...

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Unformatted text preview: © E.Garcia 2010 FST 1 – Main topics – Lecture 05 Lipids ‐ Chemically diverse group of organic compounds that are insoluble in water. They include ‐ Fats and Oils ‐ Sterols, such as cholesterol ‐ Waxes, among others. Oils (liquid at room temperature), ex.: corn oil, soybean oil, olive oil, etc. Fats (solid or semi‐solid at room temperature). Usually from animal sources, ex.: butter, lard. Fats and Oils ‐ Functions in Foods Source of energy (9 kcal/g) Carriers of fat soluble vitamins (A, D, E, K) Cooking medium (frying) Flavor, Texture Although lipids comprise a variety of chemical structures, most food lipids are TRIGLYCERIDES. Contain 3 FATTY ACIDS linked to a backbone of glycerol Simple triglycerides: contain only one type of fatty acid. Mixed triglycerides: contain at least 2 types of fatty acid Most natural fats and oils are mixtures of simple and mixed triglycerides. FATTY ACIDS are carboxylic acids with long hydrocarbon chains. They can be: ‐ Saturated fatty acids contain no carbon‐carbon double bonds, ex.: H3C‐CH2‐CH2‐CH2‐CH2‐CH2‐CH2‐CH2‐CH2‐COOH ‐ Unsaturated are subdivided in: ‐ Monounsaturated: contain one carbon‐carbon double bond, ex.: H3C‐CH2‐ CH2‐ CH2‐CH2‐CH=CH‐CH2‐CH2‐CH2‐CH2‐CH2‐CH2 ‐COOH ‐ Polyunsaturated fatty acids contain two or more double bonds: H3C‐CH2‐CH=CH‐CH2‐CH=CH‐CH2‐CH2‐CH2‐CH2‐CH2‐CH2‐CH2‐CH2‐ COOH Fatty acids in foods differ in chain length, generally from 4 C to 24 C atoms; most have an even number of C atoms. Essential Fatty Acids: cannot be made by the body; must be obtained from foods. They are: ‐ LINOLEIC Acid (ω‐6); which has 18C and 2 double bonds (18:2) ‐ alpha‐LINOLENIC Acid (ω‐3); which has 18C and 3 double bonds (18:3) To find out the omega (ω) number, count from the omega end (=methyl end; opposite to the COOH) up to the first double bond. Above are examples of ω‐3 and ω‐6 fatty acids. Common sources of Linoleic acid are oils from corn, sunflower, soybean. Alpha‐ linolenic sources are flaxseeds, walnuts, and soybean and canola oils. Some fish and fish oils supply other omega‐3 fatty acids, such as EPA* (20C and 5=) and DHA* (22C and 6=). * EPA = Eicosapentaenoic acid ; DHA = Docosahexaenoic acid Hydrogenation of oils: addition of hydrogen to double bonds. Some or all double bonds can be hydrogenated, resulting in partial or complete hydrogenation, respectively. Hydrogenation is used to convert liquid oils into more solid fats. Vegetable oils → margarine, shortening During partial hydrogenation of oils some trans double bonds can be formed. cis double bond H H I I ‐C = C‐ H I ‐C = C‐ trans double bond I H Lipids & Oxidation: a major cause of food spoilage. Unsaturated fatty acids react with oxygen leading to the production of characteristic rancid odors. Antioxidants help protect lipids against oxidation. Readings 1. McGee p.797‐801(Fats, Oils, and relatives: Lipids) 2. McGee p.37‐38 (Margarine); see also box on p.38 3. McGee p. 183 (The Benefits of Fish Oils) 4. McGee p. 189 (The Healthfulness of Fish Oils) _____________ FYI (not for exam) Fish and Omega‐3 Fatty Acids http://www.americanheart.org/print_presenter.jhtml?identifier=4632 Trans fat is double trouble for your heart health http://www.mayoclinic.com/health/trans‐fat/CL00032/METHOD=print Cholesterol Content of Foods http://www.ucsfhealth.org/adult/edu/cholesterolContent/index.html Are chicken eggs good or bad for my cholesterol? http://www.mayoclinic.com/health/cholesterol/HQ00608/METHOD=print ...
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