Lipid Oxidation. Essay

484 WordsMar 31, 20142 Pages
INSTRUCTION Oils and fat quality. Lipid oxidation. Determination of peroxide value in fats and oil. It is arguable that the two most important chemical reactions that occur in food systems are lipid oxidation and non-enzymatic browning. This lab exercise focuses attention on the former reaction. Lipid oxidation, which is also called auto-oxidation, occurs in lipid material by way of a free-radical mechanism. After an induction period, hydrogen peroxides, or primary products, are formed. Ultimately these peroxides break down, and secondary products, e.g., aldehydes, ketones, organic acids, and hydrocarbons, are formed. The peroxide value (PV) test, which is one of the most common tests used to evaluate the extent of lipid oxidation, is based on measuring peroxides. Objective: To measure the PV or a number of food samples, and to evaluate the meaning of the results. Reagents: Acetic acid (glacial) Chloroform (CCl4) 15% Potassium iodide (KI) 0.01 N (0.01M) sodium thiosulfate (Na2S2O3) Starch indicator 0.5 % concentrated hydrochloric acid HCl 0.01 N (0.00167M) potassium dichromate K2Cr2O7 (fix.) Procedure Determination of the titre of the sodium thiosulfate solution Measure off 10 ml of 0.01N K2Cr2O7 solution to a 200 ml conical flask. Add 0.5 ml concentrated HCl and 1.0 ml 15% KI solution. Mixed exactly 1 minute and leave for 5 minutes in a dark place. Add 0.5 ml starch solution, 20 ml distilled water. Mix and titrate with sodium thiosufate solution. Calculate the exact normality of Na2S2O3 knowing that in this chemical reaction 1 gram-equivalent of K2Cr2O7 react with 1 gram-equivalent of Na2S2O3 (1 mole K2Cr2O7 react with 6 moles Na2S2O3). Determination of peroxide value. Weigh 3.00 g oil (with precision of 0.001 g) into a 250 ml Erlenmeyer flask. Add 10 ml chloroform and swirl to dissolve oil. Add 15 ml acetic acid,

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