UPHESC Assistant Professor Animal Husbandry & Dairying 2025 PYQs

Concept: β-Lactoglobulin is the major whey protein of cow milk, about 50% of whey protein (≈ 9–10% of total protein); in the classical Indian dairy-chemistry tables it is given as about 0.28 g per 100 g milk.

1. Whey proteins ≈ 0.6–0.7 g/100 g milk; about half of this is β-Lg (≈ 0.3 g).
2. α-Lactalbumin ≈ 0.12, serum albumin ≈ 0.04, immunoglobulins ≈ 0.07 g/100 g.
3. 0.38–0.40 would be more than half of all whey protein, 0.20 too little; 0.28 fits best.

Short trick: β-Lg ≈ half of whey protein ≈ 0.3 g%; it is absent from human milk.

Concept: Warm-milk separation is done at about 35–40 °C (≈ 40 °C), where fat is liquid and milk viscosity is low, so separation efficiency is best.

1. Stokes' law: rate ∝ $({\rho }_s-{\rho }_f)r^2/\eta$ – heating lowers viscosity $\eta$.
2. Higher temperatures (> 45–50 °C) favour foaming and fat-globule damage; cold separation needs special separators.

Short trick: Separate cream at ≈ 40 °C (body-warm milk).

Concept: An emulsifier (mono- and diglycerides, polysorbate 80, lecithin) has both hydrophilic and hydrophobic groups, so it sits at the fat–water interface and holds the two phases together.

1. It also gives dryness and smooth texture by controlled fat destabilisation during freezing.
2. Stabilisers (gelatin, CMC, guar, carrageenan) bind water and check ice-crystal growth – they do not join fat to water.

Short trick: Emulsifier = 'two-faced' molecule (water-loving + fat-loving).

Concept: PER = weight gain (g) ÷ protein consumed (g) in growing rats. Casein, the reference protein, gives a PER of about 2.7–2.8 (adjusted to 2.5 for the ANRC standard).

1. Whey proteins / lactalbumin have higher PER (≈ 3.0–3.6) because they are richer in sulphur amino acids and lysine.
2. Total milk protein ≈ 2.8–3.1; casein is lowest among milk proteins owing to limiting methionine + cystine.

Short trick: Casein ≈ 2.7–2.8 < Milk protein ≈ 3.0 < Whey ≈ 3.2–3.6.

Concept: As per the Indian standard (IS 1166 / PFA–FSSAI), sweetened condensed milk must have not less than 9% milk fat and not less than 31% total milk solids (sugar extra, ~40–45%).

1. Unsweetened (evaporated) milk: fat ≥ 8%, total milk solids ≥ 26%.
2. Sweetened condensed skimmed milk: milk solids ≥ 26%, fat ≤ 1%.

Short trick: SCM: 9% fat + 31% milk solids ('9-31').

Concept: After pasteurisation and homogenisation (≈ 63–70 °C) the mix must be cooled at once – over a surface/plate cooler – to a low temperature and then aged at 0–5 °C for 4–24 h.

1. Quick cooling prevents bacterial growth and fat clumping and prepares the mix for ageing.
2. Of the given values only the lowest, 14 °C, lies in the cooling range; 24–44 °C are near incubation temperatures for bacteria.
3. Final ageing temperature is about 4 °C.

Short trick: Ice-cream mix: hot homogenise → cool fast → age cold (≈ 4 °C).

Concept: Fishy flavour in (especially salted, ripened-cream) butter arises when lecithin breaks down to choline and then trimethylamine, aided by acidity, salt and copper/iron.

1. Lactulose and HMF are heat-induced (Maillard) markers in milk.
2. Diacetyl gives the desirable buttery aroma; excess gives harsh 'coarse' flavour, not fishy.

Short trick: Fishy = TMA (same compound that makes fish smell).

Concept: Under FSSAI, 'ice cream' must contain only milk fat (≥ 10% for ice cream); vegetable fat/oil cannot be added.

1. A product made with vegetable fat must be labelled 'Frozen Dessert/Frozen Confection', not ice cream.
2. Medium-fat ice cream ≥ 2.5% and low-fat ice cream ≤ 2.5% milk fat – again only milk fat.

Short trick: Veg fat → not ice-cream but 'Frozen Dessert'.

Concept: PFA (now FSSAI) standard: whole milk powder – moisture ≤ 4%, milk fat ≥ 26%, titratable acidity ≤ 1.2% (as lactic acid).

1. Partly skimmed milk powder: fat 1.5–26%.
2. Skimmed milk powder: fat ≤ 1.5%, moisture ≤ 5%.

Short trick: WMP: '4% moisture, 26% fat'.

Concept: For Cheddar-type cheese, milk is standardised to a casein : fat ratio of about 0.68–0.72 (≈ 0.70), giving the legal fat-in-dry-matter (≈ 50%) and good body.

1. Too little casein (low ratio) → greasy, weak-bodied cheese with high fat loss.
2. Too high a ratio → hard, dry cheese with low FDM.
3. Corresponding protein : fat ratio ≈ 0.85–0.9.

Short trick: Cheddar milk: Casein/Fat ≈ 0.7.

Concept: A synbiotic (printed 'symbiotic') is a product that combines probiotics (live beneficial microbes, e.g. Lactobacillus, Bifidobacterium) with prebiotics (non-digestible substrates such as inulin, FOS, GOS) that feed them.

1. The prebiotic improves survival and colonisation of the probiotic.
2. Antibiotics kill microbes; abiotic means non-living; biostatic means growth-inhibiting.

Short trick: Pro + Pre = Syn(biotic) – 'synergy'.

Concept: Cheese hardness depends mainly on moisture content. If only a small part of the whey is expelled (little cutting, cooking, pressing), the curd keeps much moisture and a soft cheese results.

1. Soft cheeses (Cottage, Camembert, Brie) have > 50–55% moisture; hard cheeses (Cheddar, Parmesan) < 40%.
2. The amount of milk used affects yield, not texture.

Short trick: Less whey removed → more moisture → softer cheese.

Concept: Rennet, extracted from the fourth stomach (abomasum) of suckling calves, contains about 80–90% chymosin (rennin) and 10–20% pepsin.

1. Chymosin specifically cleaves κ-casein at Phe₁₀₅–Met₁₀₆, destabilising micelles so that milk coagulates.
2. Plasmin is the native alkaline protease of milk; catalase is an indicator of mastitis/heat.

Short trick: Rennet = Chymosin (κ-casein 105–106).

Concept: For a therapeutic effect, a probiotic food should contain at least ${10}^6$ cfu per ml (or g) of viable organisms at the time of consumption (daily intake about ${10}^8$–${10}^9$ cells).

1. FSSAI and most international guidelines use ≥ ${10}^6$ cfu/g (some ≥ ${10}^7$).
2. ${10}^{15}$ or ${10}^{20}$ cfu/ml is physically impossible – far more cells than can fit in 1 ml.

Short trick: Probiotic 'therapeutic minimum' = ${10}^6$ (million) per ml.

Concept: Co-precipitates are made by heating skim milk (to bring whey proteins down with casein) and precipitating with CaCl₂ and/or acid. High-calcium co-precipitates are poorly soluble.

1. Calcium cross-links casein (calcium caseinate–phosphate bridges), so the higher the Ca, the lower the solubility.
2. Low-calcium (acid-precipitated, neutralised with alkali) co-precipitates are the soluble types used in foods.

Short trick: More Ca = more cross-links = less soluble.

Concept: Protein content of cheese rises as moisture and fat fall: soft/semi-hard < hard < very hard skim-milk cheese.

1. Sapsago (Swiss Schabziger) is a very hard, dried skim-milk cheese, so it has the highest protein – 49.4%.
2. Parmesan (grated, very hard, part-skim, ~30% moisture) – 41.6%.
3. Cheddar (≈ 37% moisture) has more protein than the moister Gouda (≈ 41–43%): Cheddar 29.6%, Gouda 26.0%.
4. Code: a – 1, b – 3, c – 2, d – 4.

Short trick: Drier and leaner the cheese, higher the protein: Sapsago > Parmesan > Cheddar > Gouda.

Concept: Butyric acid (C4:0) is the characteristic short-chain fatty acid of ruminant milk fat; in buffalo milk fat it is about 3.6% (by weight of fatty acids), slightly higher than in cow milk fat (≈ 3.0–3.4%).

1. Butyric acid is the basis of the Reichert–Meissl value (volatile, water-soluble fatty acids) used to detect ghee adulteration.
2. It is absent from vegetable oils and body fats, so its presence identifies milk fat.

Short trick: Buffalo fat butyric ≈ 3.6 > cow ≈ 3.2.

Concept: The Farrall index is the standard microscopic measure of homogenisation efficiency: a diluted milk sample is examined and globules larger than 2 µm are counted.

1. Farrall index 0–10: lower values mean better homogenisation (< 4–6 is acceptable for market milk).
2. Other checks are the USPHS test (fat difference between top 100 ml and the rest after 48 h) and the NIZO method; 'creaming index' is not the recognised index for homogenisation.

Short trick: Homogenisation efficiency → Farrall index (microscope, globules > 2 µm).

Concept: Homogenisation (≈ 2000–2500 psi at 60–65 °C) breaks fat globules from 2–10 µm (avg ≈ 3.5 µm) to below ~1–2 µm, so their number rises about 10,000-fold.

1. Number ∝ $1/d^3$ for the same fat volume, so even a modest cut in diameter multiplies the number enormously.
2. Surface area increases 4–10 times; new membrane is formed from casein and whey protein, so no cream line forms.

Short trick: Homogenisation: ~10,000× more globules, no cream line.

Concept: In standard dairy texts, homogenised milk is defined as milk in which fat globules have been reduced to 2 µm or less in diameter, so that no visible cream layer forms in 48 h.

1. Raw milk globules: 0.1–15 µm, mostly 2–6 µm (average 3–4 µm).
2. That is why the Farrall index counts globules larger than 2 µm as un-homogenised.

Short trick: Homogenised milk = fat globules < 2 µm.