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Lab 4 - Lipid analysis docx

Lab 4 - Lipid analysis docx - Food Analysis 4321C...

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Food Analysis 4321C Laboratory #4A: Determination of Free Fatty Acids and Peroxide Value in Vegetable Oil Background information: Nielson Chapters 13-14 1. Background Vegetable oil is extracted from oil seeds (e.g. peanuts, soy beans) using hexane extraction. Hexane is removed by evaporation and distillation. The crude oil contains free fatty acid, phospholipids, colorants, and odors that can be removed in different steps of refining process. Refined vegetable oils contain almost only triglycerides. Fatty acids in triglyceride can be saturated or unsaturated. Saturated fatty acids are stable during storage. The double bonds in unsaturated acid can be oxidized by oxygen in the air. This reaction takes place spontaneously (auto-oxidation) or is catalyzed by light (photo-oxidation). Auto-oxidation can be accelerated by transitional metal ions (e.g. Cu 2+ ) and higher temperature. Oxidation is the major factor that determines the shelf life of vegetable oils. Without proper protection, oils with high levels of polyunsaturated fatty acids (e.g. flaxseed oil or fish oil) will go bad (rancidity) in a few days. Oxidation of lipids generates lipid peroxides (also called hydro-peroxide). Lipid peroxides are the primary reaction products of lipid oxidation. Progression of oxidation on peroxides leads to the production of a number of secondary products which include malonaldehyde, a potent carcinogen. Lipid oxidation also takes place in human body, a process associated with oxidative stress and aging. 1
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2. Reagents Phenolphthalein indicator (1% in alcohol) Saturated potassium iodide (KI) Standardized NaOH solution (0.10 mol/L in water) Sodium thiosulfate (0.01 mol/L in water) Starch solution (1% in water) Mixture of acetic acid and chloroform (3:2, v/v) 3. Lipid Samples Groups Samples 1 Peanut oil, oxidized peanut oil* 2 Soybean oil, oxidized soybean oil 3 Corn oil, oxidized corn oil 4 Olive oil, oxidized olive oil 5 Canola oil, oxidized canola oil *Oils are oxidized for 2 days in a 60 o C oven. 4. Free Fatty Acid (FFA) Analysis FFA measures the concentration of fatty acids that are released from a triacylglycerols (lipid) due to hydrolysis, lipase action, or even oxidation. It is a good indicator of oil quality or the extent of oil refining. 1. Weigh 5 g (accurate to the second decimal place ) of oil sample into a 250-mL wide mouth Erlenmeyer flask. You will need two flasks for oil and another two flasks for the oxidized oil . (Caution: An empty 250-mL Erlenmeyer flask weighs over 110 g, which is over the allowed Max weight for some analytical balances.) 2. In the fume hood, add 50 mL of ethanol to dissolve the oil. Also prepare a blank that contains 50 mL of ethanol. (5 flasks total) 3. Gently swirl the ethanol to complete dissolve the oil. Place stopper on flasks.
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