Biochemistry & Food Chemistry — Carbohydrates, Proteins, Vitamins, Enzymes & Food Preservation

Overview

Biochemistry and food chemistry form one of the most consistently tested areas in UPSC Prelims, particularly vitamins and their deficiency diseases, food preservation techniques, and the basics of biomolecules. This chapter covers the four major classes of biomolecules (carbohydrates, proteins, lipids, and nucleic acids), vitamins and minerals with their deficiency diseases, enzymes, and food safety — including adulteration detection and preservation methods.

Exam Strategy: The vitamin-deficiency disease table is a Prelims favourite — memorise it thoroughly. Questions on food preservation (pasteurisation, irradiation, lyophilisation) and food adulteration (FSSAI role) appear regularly. For Mains GS3, understanding of food security, nutrition programmes, and FSSAI's regulatory framework is valuable.

Carbohydrates

Carbohydrates are organic compounds made of carbon, hydrogen, and oxygen, with the general formula C_x(H₂O)_y. They are the primary source of energy for living organisms.

Classification of Carbohydrates

Important Polysaccharides

Prelims Tip: Cellulose is the most abundant organic compound on Earth. Humans lack the enzyme cellulase needed to digest it, but it serves as essential dietary fibre. Ruminants (cows, goats) can digest cellulose because of cellulase-producing bacteria in their rumen.

Proteins

Proteins are polymers of amino acids linked by peptide bonds. They are essential for growth, repair, enzyme activity, immunity, and virtually every biological process.

Amino Acids

• There are 20 standard amino acids used by the human body
• Essential amino acids (9) — cannot be synthesised by the body; must be obtained from diet (e.g., leucine, lysine, tryptophan, valine, methionine, phenylalanine, threonine, isoleucine, histidine)
• Non-essential amino acids (11) — can be synthesised by the body

Protein Structure

Denaturation

Denaturation is the loss of a protein's 3D structure (and hence its biological function) due to heat, pH change, or chemical agents. Example: cooking an egg causes the albumin protein to denature (it turns white and solid).

Types of Proteins by Function

Lipids (Fats and Oils)

Lipids are hydrophobic biomolecules that include fats, oils, waxes, and steroids. They serve as energy reserves, insulation, and components of cell membranes.

Types of Fatty Acids

Important: FSSAI has capped trans fat content in oils and fats at 2% (effective from 1 January 2022), aligning with WHO recommendations. India became one of the first countries to adopt this stringent limit. Trans fats are linked to cardiovascular disease.

Cholesterol

• A type of lipid (steroid) essential for cell membrane structure, vitamin D synthesis, and hormone production
• HDL (High-Density Lipoprotein) — "good cholesterol"; removes cholesterol from arteries
• LDL (Low-Density Lipoprotein) — "bad cholesterol"; deposits cholesterol in artery walls

Vitamins

Vitamins are organic compounds required in small quantities for normal metabolic functioning. The body generally cannot synthesise them (except vitamin D and vitamin K in limited amounts), so they must be obtained from the diet.

Fat-Soluble Vitamins (A, D, E, K)

These dissolve in fat, are stored in the liver and adipose tissue, and do not need daily replenishment.

Water-Soluble Vitamins (B-complex and C)

These dissolve in water, are not stored in the body (except B₁₂), and must be consumed regularly.

Mnemonic for Pellagra (B₃ deficiency): The "3 Ds" — Dermatitis, Diarrhoea, Dementia. If untreated, a 4th D — Death.

Key Distinction: Vitamin B₁₂ is the only water-soluble vitamin stored in the body (in the liver, for up to 3–5 years). It is also the only vitamin that contains a metal ion (cobalt). Strict vegetarians/vegans are at risk of B₁₂ deficiency since it is absent in plant-based foods.

Minerals

Minerals are inorganic elements essential for various physiological functions.

Prelims Alert: India's National Goitre Control Programme (renamed National Iodine Deficiency Disorders Control Programme — NIDDCP) mandates the use of iodised salt. Iodine deficiency is the most common cause of preventable intellectual disability worldwide.

Enzymes

What Are Enzymes?

Enzymes are biological catalysts — proteins that speed up chemical reactions in living organisms without being consumed in the process. They lower the activation energy required for a reaction.

Key Properties of Enzymes

Important Digestive Enzymes

Key Concept: Lactose intolerance occurs when the body produces insufficient lactase enzyme, making it unable to digest lactose (milk sugar). It is common in adults, especially in East Asian and some Indian populations.

Industrial Applications of Enzymes

Nucleic Acids — DNA and RNA Basics

DNA (Deoxyribonucleic Acid)

RNA (Ribonucleic Acid)

Prelims Tip: Chargaff's rule states that in DNA, the amount of adenine equals thymine (A = T) and guanine equals cytosine (G = C). This rule does not apply to single-stranded RNA.

Food Adulteration and FSSAI

Food Safety and Standards Authority of India (FSSAI)

Common Food Adulterants

Food Preservation Methods

Food preservation prevents microbial growth and spoilage, extending shelf life.

Prelims Tip: Pasteurisation is named after French microbiologist Louis Pasteur. The HTST (High Temperature Short Time) method heats milk to 72 °C for 15 seconds and then rapidly cools it. UHT (Ultra-High Temperature) processing heats milk to 135–150 °C for 2–5 seconds, allowing storage without refrigeration for months.

Key Distinction: Food irradiation does NOT make food radioactive. It uses gamma rays (from Cobalt-60 or Caesium-137), electron beams, or X-rays to destroy bacteria, parasites, and insects. India approved irradiation of onions, potatoes, and spices for the domestic market in 1994.

Frequently Asked Questions (Prelims Pattern)

Key Terms for Quick Revision

Sources: Wikipedia; Britannica; FSSAI (fssai.gov.in); PMC (NCBI); PIB (pib.gov.in); PMF IAS; BYJU'S Biology.