FATS AND OILS COMPILED BY: VANDANA MAHAJANI
STRUCTURE,RANCIDITY AND REVERSION • They are composed of fatty acid and glycerol linked together to form ester. • Rancidity: • The development of any disagreeable odour and flavour in fats and oils causing spoilage is called rancidity • It occurs in pickles, cakes, fried snacks, cheese and salad dressings. • Vegetable oils resist oxidation due to presence of Vit or tocopherols • Reversion • The change in flavor before it actually becomes rancid is reversion. • Flavour may be fishy, buttery, beany, painty, or grassy
Effect of heat on fats • There is increase in free fatty acids • Smoke point is lowered • Iodine number decreases • Melting point falls • Fat turns darker in colour • Fat gets polymerised • Refractive index increases • POLYMERISATION: • This occurs when fats are subjected to intense heat. Free fatty acids are released, colour darkens and gum is formed at the edge of the vessel.
EXTRACTION OF FATS AND OILS • Rendering: used for extracting fat from animal tissues. Chopped tissue is subjected to intense heat in 1. presence of water, 2. absence of water. • Pressing: Used for removing poil from oilseeds or fruit rich oils.. The oil bearing tissues are rolled , crushed or ground into flakes, and then heated by steam at 70 deg. C. • Solvent extraction: This is done to extract remaining oil from the seed cake.
Refining, Winterization and Hydrogenation • Refining is done by • Filtering • Degumming • Bleaching • Steam deodorization • WINTERIZATION • After steam D. the oils are cooled rapidly and filtered. Such oils do not turn cloudy on refrigeration and have high melting points. • HYDROGENATION • Liquid oils are converted into solid fats by this process • Hydrogen is used under pressure.
Shortenings • The shortening ability of the fats is measured by a shortometer which measures the load required to break a pastry. • The fat that covers the greatest surface area of the flour particles is supposed to have the greatest shortening power. • Diet margarines, peanut butter, cheese spread, garlic spread, tofu spread are other fats available. • Suet is the solid fat deposited around the kidneys of animals. • Commercial uses of fat • 1. increase tenderness 2. form emulsions. 3. spread 4. fry and cook. • 5. get cream and foams 6. impart flavour, aroma, and colour to food.
Cholesterol • It is a fat like substance present in food • It is present in animal foods only. • It can be synthesized by the body • Milk, ghee, butter, cream, organ meats, egg yolk and shell fish are rich sources of cholesterol. • Functions of cholesterol • A precursor for sex hormones. • A precursor of vitamin D • It is required for the formation of bile. • It is an essential constituent of cell membrane