Thermal packaging principles for indigenous desiccated dairy products:
(A), (C), (D) Packing khoa at cooler or intermediate temperatures ($40\text{--}70^\circ\text{C}$) leaves packaging headspace prone to airborne mould spore recontamination (Penicillium, Aspergillus), resulting in surface fungal growth within 3 to 5 days at ambient storage.
(B) Packaging freshly prepared khoa while hot at $80\text{--}90^\circ\text{C}$ into food-grade laminated pouches or containers utilizes residual product sensible heat to pasteurize the container's interior surfaces and packaging headspace. This thermal lethal effect prevents post-processing contamination by aerial moulds and yeasts, effectively prolonging shelf-life from just 3-4 days to 14-21 days at $37^\circ\text{C}$.

Thermal severity hierarchy in dairy product manufacturing:

• Khoa (B): Subjected to extensive open-pan boiling, continuous evaporation, and high heat desiccation ($\gt 100^\circ\text{C}$ for extended periods), producing severe Maillard browning, massive whey protein denaturation, and lactosylation (highest heat changes).
• Paneer (A): Milk is heated to $85\text{--}90^\circ\text{C}$ for 5 minutes prior to acid coagulation at $70^\circ\text{C}$, inducing significant whey protein denaturation ($\gt 75\%$) and coprecipitation with casein.
• Chakka (C): Prepared by fermenting pasteurized milk ($72^\circ\text{C}$ for 15 s) into dahi at mesophilic temperatures ($22\text{--}30^\circ\text{C}$) followed by whey drainage.
• Acid casein (D): Coagulated at mild isoelectric precipitation temperatures ($43\text{--}45^\circ\text{C}$) using dilute mineral acid from skim milk with minimal thermal exposure.

Colloidal chemistry of paneer acid-heat coagulation:

• Statement (I) is correct: When hot milk ($80\text{--}85^\circ\text{C}$) is acidified to $pH \approx 5.3\text{--}5.4$ with citric/lactic acid, colloidal calcium phosphate (CCP / tricalcium phosphate) dissolves progressively from the micellar framework into the serum phase, eliminating electrostatic charge stabilization.
• Statement (II) is correct: Concurrently, the net negative surface charge on the casein micelles drops towards zero (isoelectric destabilization). The colloidal dispersion collapses, precipitating a continuous three-dimensional porous casein-whey protein matrix that mechanically traps and embeds milk fat globules into the cohesive curd structure.

Chemical reactions during open-pan heat desiccation of milk (Khoa, Peda, Rabri):

• Enzymatic browning involves polyphenol oxidase (occurring in fruits, not heated milk where all enzymes are destroyed).
• In heat-desiccated milk products, non-enzymatic browning (the Maillard reaction between reducing milk lactose and the $\epsilon$-amino group of casein lysine, along with lactose caramelization) is the predominant biochemical pathway responsible for generating melanoidin brown pigments and aromatic carbonyls, pyrazines, and maltol that impart the characteristic rich cooked, nutty, caramelized flavour and brown hue.
  (C), (D) contribute partially to texture and off-flavors, but color and cooked taste are driven by non-enzymatic browning.