Manufactured & Traditional Dairy Products

Determinants of milk powder solubility and insolubility index:

• Antibiotic residues inhibit starter culture fermentation but have no direct effect on milk protein physical solubility.
• Chilled storage causes slight reversible beta-casein dissociation, which reassociates upon preheating without permanently impairing powder reconstitution.
• Disturbed salt balance (elevated ionic calcium and magnesium relative to citrates and phosphates) causes pronounced casein micelle aggregation and irreversible protein denaturation during high-temperature preheating and spray drying, resulting in a significantly elevated insolubility index (higher insoluble sediment upon reconstitution).
• Late lactation milk alone without severe mineral imbalance does not explain high insolubility indices in well-controlled commercial manufacturing.

Heat classification of skim milk powder:

• The Whey Protein Nitrogen Index (WPNI, expressed in mg undenatured whey protein nitrogen per gram of powder) is the international standard (ADMI) for heat classification: Low-heat powder has $\ge 6.0\text{ mg WPN/g}$, Medium-heat powder has $1.51\text{--}5.99\text{ mg WPN/g}$, and High-heat powder has $\le 1.50\text{ mg WPN/g}$.
• PDCAAS evaluates nutritional protein quality and amino acid digestibility, not industrial thermal history.
• Urea number evaluates non-protein nitrogen or adulteration.
• DIAAS is an advanced nutritional metric of ileal amino acid digestibility.

Air occlusion in milk powder particles:

• Spray dried milk powder consists of spherical particles containing central air vacuoles (occluded air) entrapped during atomization and rapid droplet drying.
• Instantized milk powder contains agglomerated porous clusters with significant interstitial and occluded air.
• Roller dried (drum dried) milk powder is produced by spreading a thin film of concentrate over steam-heated drums, which is scraped off by doctor blades and ground into flat, solid, irregular flakes that contain virtually zero occluded air and have high free fat.
• Fluid bed dried powders contain significant internal and inter-particle air.