Lipids Lecture 2 - Triglycerides

Introduction to Lipids

  • This lecture series focuses on lipids, covering structures, functions, reactions, and classifications.

  • Specific focus on triacylglycerols (triglycerides).

Triglycerides (Triacylglycerols)

  • Definition: Fatty acids and glycerol that serve as long-term energy storage and insulation in organisms.

  • Excess caloric intake leads to storage as triglycerides in adipose tissue.

A) Structure

  • Comprised of one glycerol molecule (1,2,3-propanetriol) and three fatty acids.

  • Fatty acids can be identical or different.

  • Molecular representation:Triglyceride Structure

Properties of Triglycerides

  • Solubility: Not soluble in water due to large nonpolar structure.

  • States at Room Temperature:

    • Fats: Solid (typically from animals).

    • Oils: Liquid (usually from plants).

  • Melting Points:

    • Fatty acids with more unsaturation (double bonds) have lower melting points and remain liquid.

    • Saturated fats stack more efficiently, resulting in solid forms.

  • Example Triglyceride Sources:

    • Butter (~30% unsaturated)

    • Peanut oil (~80% unsaturated)

B) Reactions

  • Key reactions include saponification, oxidation, and hydrogenation.

Saponification

  • Hydrolysis of triglycerides in the presence of a strong base (like KOH) to produce carboxylate salts (soap).

  • Results in fatty carboxylate salts with both nonpolar and ionic properties, facilitating interactions with diverse substances (micelles formation).

  • Historical context: Homemade soap production using animal fats and wood ashes (source of OH-).

Oxidation

  • Occurs naturally over time due to exposure to oxygen, leading to rancidity (smell due to generation of short-chain carboxylic acids).

  • Oils are more susceptible to oxidation than fats due to higher double bond counts leading to shorter shelf life.

Hydrogenation

  • The process of adding hydrogen to unsaturated fatty acids in triglycerides to convert them into alkanes, preserving the ester bonds.

  • Post-WWII, hydrogenation was used to solidify vegetable oils for longer shelf life and to alter properties (e.g., Crisco).

  • Benefits include increased shelf life, cost-effectiveness, and tailored product attributes but can lead to trans fats.

  • Trans fats pose health risks, linked to heart disease; therefore, labeling requirements and bans are in effect for processed foods.

Additional Discussion Points

  • Physiological differences in the metabolism of short, medium, and long-chain fatty acids.

  • Exploration of health impacts based on types of fatty acids consumed.

  • Identification of sources rich in medium-chain versus long-chain fatty acids.

Conclusion

  • Review and understand the reactions of triglycerides as discussed in previous organic chemistry contexts.