What would be the effect of a higher time-temperature combination (78°C for 66s) during pasteurisation on proteins in skim milk? Is this likely to cause any denaturation?

Jithesh Janardhanan, New Zealand (Aotearoa)

Milk has two major proteins: casein (about 80%) and whey protein. In the presence of heat casein protein is quite stable whereas whey protein is unstable and starts to denature, by forming minute particles that subsequently gather and precipitate.

The degree of denaturation depends on the temperature and the period of time. The usual pasteurization process heats milk to 70 – 75 °C for 15 seconds and causes only marginal denaturation and since the minute particles of whey protein are present only in very small amounts, hardly any precipitation occurs. Every increase in the time-temperature combination results in greater denaturation. Casein micelles will irreversibly aggregate only if you heat milk above the boiling point for a long time.