LIPIDS:

WHAT ARE LIPIDS:

• Compounds → soluble in organic solvents

  • Nonpolar molecules

• fats/oils, fatty acids. Waxes, cholesterol, membrane lipids, vitamins: A, D, E, K

• 9 kcal/g

POLAR AND NONPOLAR COMPOUNDS:

• How electrons are shared between atoms

  • Electronegativity

• Polar = not shared equally

• Nonpolar = relatively equally

• Some atoms = more electronegative than others → unequal pull

• Determines solubility

  • “Like dissolves like”

    • Nonpolar substance + nonpolar solvent = soluble

    • Polar substance + polar solvent = soluble

    • Nonpolar substance + polar solvent = insoluble

WHY LIPIDS ARE WATER INSOLUBLE:

• Electronegative

  • Oxygen

  • Nitrogen

• Not electronegative

  • Hydrogen

  • Carbon

• Water = Hydrogen + Oxygen = polar

• Lipids = Hydrogen + carbon = nonpolar

LIPIDS IN FOODS:

• Exist in food at triacylglycerols (TAGs)

  • Triglycerides

• Composition: glycerol backbone + 3 fatty acids

FATTY ACIDS (FA): THE BUILDING BLOCKS OF TRIGLYCERIDES

• Classified based on structure

• Length of fatty acid (short, med, long)

• Saturated vs. unsaturated fatty acids

• Foods + triglycerides = contain fatty acids

  • Butter

    • 80% fat

      • 97% triglycerides

        • 50-70% saturated fatty acids

        • 26% unsaturated fatty acids

• Saturated FA

  • Higher melting point

    • Solid at room temp

  • More stable

  • Increased risk of heart disease → more negative health associations

• Unsaturated FA

  • Lower melting point

    • Liquid at room temp

  • Prone to oxidation reactions

  • Positive for nutrition

UNSATURATED FATTY ACIDS: 

• Unsaturated = determines its stability in a food system

• Monounsaturated (MUFA) = 1 double bond

• Polyunsaturated (PUFA) = 2+ double bonds

  • More double bonds → less stab;e + more reactive lipid = risk of spoilage faster

• Classify unsaturated fats → direction of double bonds

  • Cis: R groups on same side

  • Trans: R groups on opposite sides

    • Hydrogenations

      • Unsaturated fats → more saturated

    • Partially hydrogenated oils (PHOs) = no longer considered GRAS by the FDA

      • PHOs = primary source of trans fatty acids

    • Increases LDL cholesterol → associated with increased risk of coronary heart disease

  • Influences shape of fat molecule

  • Most double bonds in lipids are cis

  • Essential = body cannot make it → acquired through diet

    • Alpha-linolenic acid (ALA): Type of Omega 3 FA

    • Linoleic acid (LA): Type of Omega 6 FA

OTHER LIPIDS: PHOSPHOLIPIDS:

• Phosphate head with 2 fatty acid tails

• Phosphate = polar region

• Fatty acids = nonpolar region

• Interact with both lipids and water

• Lipids in egg yolk

  • 65% neutral lipids

  • 30% phospholipids

  • 5% cholesterol

    • Found in animals (not plants)

    • Accumulate in the body

      • Foods we eat

      • Produced by body

    • High cholesterol in body = many factors

    • Hydrophobic (nonpolar)