Dairy Chemistry- ICAR JRF/SRF 2024

• Thiobarbituric Acid (TBA) Assay for Lipid Oxidation:
• Biochemical Basis:
• Evaluates secondary lipid peroxidation in milk fat and meat tissues.
• Measures malondialdehyde (MDA), a three-carbon dialdehyde cleaved from polyunsaturated fatty acid hydroperoxides.
• Two molecules of 2-thiobarbituric acid condense with one molecule of malondialdehyde under acidic, boiling conditions to form a pink chromogen exhibiting maximal absorbance at $532\text{ nm}$.
• Conclusion: Malanoaldehydes (Option 2).

Correct option: (2) Malanoaldehydes

• Lecithination in Instant Milk Powder Manufacturing:
• Role of Lecithin:
• In instant whole milk powder production, lecithin (phosphatidylcholine fraction) dissolved in butter oil is sprayed onto warm powder granules ($0.2\%$ by weight).
• Serves as an amphiphilic surfactant that coats surface free fat, lowering interfacial tension and promoting rapid capillary water penetration, wettability, and sinkability in cold water.
• Conclusion: Lecithin (Option 4).

Correct option: (4) Lecithin

• Phospholipid Distribution Across Dairy Fractions:
• Enrichment in Buttermilk:
• Milk phospholipids are predominantly concentrated in the Milk Fat Globule Membrane (MFGM).
• During churning of cream into butter, mechanical agitation ruptures fat globule membranes, releasing MFGM polar lipid fragments into the aqueous buttermilk.
• Consequently, buttermilk is the richest dairy source of phospholipids ($0.15 - 0.20\%$, or $\approx 5\times$ higher than whole milk).
• Conclusion: Butter milk (Option 2).

Correct option: (2) Butter milk

• Nutritional and Energetic Characteristics of Dietary Fats:
• Caloric Density:
• Fats yield $9\text{ kcal/g}$ ($37\text{ kJ/g}$), over double the energy of carbohydrates and proteins ($4\text{ kcal/g}$).
• Official Answer Key: Designated Option 3 as the target choice.
• Conclusion: Fats are a concern because they have a high caloric density (Option 3).

Correct option: (3) Fats are a concem because they have a high caloric density of

Analyzing the statements in relation to Acid base equilibria:

The correct option is Option 2: No. of double bond 2, autooxidation products formed 3.