Lecture on fat

Lecture on Lipids

Definition of Lipids

  • Lipids: General term for fats, oils, and waxes, though the class focuses on fats and oils only.

Sources of Fats

  • Animal Fats:

    • Butter: Fat from milk

    • Lard: Fat from pork

    • Suet: Fat from beef

  • Plant Oils:

    • Oils derived from various plants such as:

    • Olives

    • Palms

    • Coconut

    • Corn

    • Soybeans

    • Peanuts

Functions of Fats in Food

  • Flavor:

    • Fats have intrinsic flavors (e.g., butter, lard, olive oil).

    • Act as carriers of flavor, making flavor compounds more soluble.

    • Skimming too much fat diminishes flavor intensity.

    • Absorb odors; example: butter can taste like refrigerator odors when stored uncovered.

    • Suppress bitterness by solubilizing bitter compounds.

  • Role in Emulsions:

    • Blend of oil and water creating creamy/smooth textures in foods.

  • Frying Medium:

    • Fats transfer heat from cookware to food.

    • Water boils at 212°F but oil can reach 350–400°F for rapid cooking.

    • High temperatures facilitate Maillard reactions, enhancing flavor and color.

  • Greasing Pans:

    • Prevents sticking of food during cooking.

  • Separating Starch:

    • Ensures smooth sauces or gravies by preventing clumping of starch particles.

  • Tenderizing Baked Goods:

    • Contributes to softer texture in cakes, pancakes, and biscuits.

    • Excess fat can lead to overly crumbly textures.

  • Aeration of Batters:

    • Incorporating air into fat during mixing leads to lighter, leavened products.

  • Anti-foams:

    • Work against foam formation in certain food preparations.

Structure of Fats

  • Basic Structure:

    • Composed of glycerol and fatty acids.

  • Glycerol:

    • A three-carbon molecule with hydroxyl groups connected to each carbon atom.

  • Fatty Acids:

    • Characterized by a carboxyl group at one end and a hydrocarbon chain (R group).

    • Length of Carbon Chains:

    • Shortest: 2 carbons.

    • Longest: up to 28-30 carbons.

  • Saturation vs. Unsaturation:

    • Saturated Fatty Acids: No double bonds between carbon atoms.

    • Unsaturated Fatty Acids: One or more double bonds exists within the carbon chain.

    • Monounsaturated: 1 double bond

    • Polyunsaturated: 2 or more double bonds

Physical Properties of Fats

  • Solubility:

    • Fats dissolve in other fats or lipids; fat-soluble structures lack affinity for water.

    • Water-soluble compounds often contain hydroxyl groups or double bonds with oxygen.

  • Melting Point:

    • Influenced by fatty acid characteristics:

    • Shorter carbon chains yield lower melting points.

    • Longer chains have higher melting points.

    • Saturated fatty acids have higher melting points due to structural packing.

    • Increased double bonds lower melting points (e.g., stearic acid vs. oleic acid).

Examples of Saturated vs. Unsaturated Fatty Acids

  • Butyric Acid: 4 carbons, melts at -5°C (characteristic of rancid milk).

  • Stearic Acid: 18 carbons, no double bonds, solid at room temperature.

  • Oleic Acid: 18 carbons, 1 double bond, liquid at room temperature (main fat in olive oil).

  • Linoleic Acid: 18 carbons, 2 double bonds, remains liquid in refrigeration (soybean oil).

Plastic Fats

  • Definition: Solid fats like butter and margarine that exhibit plastic behavior are mixtures of fat crystals and oil.

  • Properties: When pressed, they retain indentation (plastic) unlike elastic materials which bounce back.

  • Plastic Range: Refers to the temperature range where solid fats transition to liquid; they do not have a specific melting point.

Deterioration of Fats

  • Rancidity: A deteriorated fat is referred to as rancid. Two main types of rancidity exist:

    • Hydrolytic Rancidity:

    • Caused by heat or enzymes (lipases) breaking fat into glycerol and free fatty acids.

    • Produces undesirable odors such as butyric acid after butter is heated.

    • Leads to formation of acrolein at the smoke point, indicating further breakdown.

    • Oxidative Rancidity:

    • Occurs mainly in unsaturated fats leading to off-flavors, destruction of desirable flavor, and fat-soluble vitamins.

    • Influenced by:

      • Metals (copper, iron) that catalyze reactions.

      • High temperatures increase reaction rates.

      • Oxygen access, with higher surface area leading to faster reactions.

      • Enzymatic activity from lipoxygenases present in fatty foods (e.g., soybeans, olives).

      • Presence of antioxidants (e.g., BHA, BHT, tocopherols) can mitigate oxidation.

Fat Substitutes

  • Sucrose Polyester (Olestra/Olean): A fat-like compound made from sucrose and fatty acids, non-digestible and calorie-free.

  • Salatrim: Combines short-chain fatty acids with stearic acid to be lower in calories but maintaining fat properties.

  • Simplesse: Derived from milk or egg white proteins, creates microscopic droplets that mimic the texture of fats.

  • Oatrim: Derived from oat fiber (beta-glucan), gives off a slippery feeling characteristic of fats, used in frozen products.