🍲 Proteins and Lipids in Foods

This lesson explains core food science and nutrition concepts with practical relevance to food quality, safety, and human health.

---

Proteins and Lipids in Foods

Proteins

Proteins are macromolecules composed of amino acid chains linked by peptide bonds. They perform diverse functions in foods including structural roles (gluten in wheat), enzymatic activity, and nutritional value. Proteins provide approximately 4 kcal of energy per gram.

Amino Acids

There are 20 standard amino acids, of which 9 are essential (cannot be synthesized by the body and must be obtained from diet): histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

Protein Quality

• Complete proteins — contain all essential amino acids in adequate proportions (e.g., egg, milk, meat, fish, soybean)
• Incomplete proteins — deficient in one or more essential amino acids (most plant proteins)
• Limiting amino acid — the essential amino acid present in the lowest proportion relative to requirements (lysine in cereals, methionine in legumes)

Food Sources

Animal sources include milk, eggs, meat, and fish. Plant sources include pulses, soybeans, nuts, and cereals. Mutual supplementation of cereals and pulses (e.g., rice + dal) provides complementary amino acids and improves overall protein quality.

Lipids

Lipids are a diverse group of hydrophobic compounds including fats, oils, waxes, and phospholipids. Fats provide 9 kcal of energy per gram, making them the most energy-dense macronutrient.

Fatty Acids

• Saturated fatty acids (SFA) — no double bonds; found in ghee, butter, coconut oil, palm oil; excessive intake linked to cardiovascular disease
• Monounsaturated fatty acids (MUFA) — one double bond; found in olive oil, groundnut oil, mustard oil
• Polyunsaturated fatty acids (PUFA) — multiple double bonds; include omega-3 (alpha-linolenic acid) and omega-6 (linoleic acid) families

Essential Fatty Acids

Linoleic acid (omega-6) and alpha-linolenic acid (omega-3) are essential fatty acids that must be supplied through diet. They are precursors of eicosanoids (prostaglandins, thromboxanes) and are critical for brain development, immune function, and cardiovascular health. Rich sources include flaxseed, walnuts, fish oil, soybean oil, and sunflower oil.

Role of Lipids in Foods

Lipids contribute to flavor, texture, and mouthfeel of foods. They serve as carriers for fat-soluble vitamins (A, D, E, K) and provide essential fatty acids. In food processing, lipid oxidation is a major cause of rancidity and off-flavors.

---

Summary Cheat Sheet

Topic	Key takeaway
Main focus	Proteins and lipids in foods — amino acids, essential fatty acids, and food sources.
Section context	Revise this lesson with the rest of Principles of Food Science and Nutrition for stronger conceptual continuity.