Can the processing of milk protein lower its quality?
Milk is often heated to increase its microbiological safety and shelf life, or to make specific milk-based products (such as infant formulas and protein supplements).
Heating of milk can cause its sugar molecules (lactose) to stick to the amino acids of the milk protein, a process known as glycation. Especially the essential amino acid lysine is susceptible to this. This may interfere with the digestion and/or absorption of lysine in the protein.
Our study investigated the effect of glycation of milk protein on plasma amino acid responses during the 6 hours after ingestion. Participants ingested three different protein drinks on three different days: 40 g of 3%, 20%, or 50% glycated milk protein.
The highly glycated milk protein severely impaired lysine bioavailability: the incremental area under the curve of plasma lysine concentration was 92% lower.
This suggests that glycation can negatively influence the digestion and absorption of the lysine. This lower lysine bioavailability may have metabolic consequences (for example, lower muscle protein synthetic response). However, this remains to be established.
Unfortunately, there is no way to know how glycated specific protein products are. But if more research shows glycation can have an impact on protein quality, perhaps it will become common practice to report it on the label.
Go to the next infographic in the protein series:
Our new study: milk processing lowers protein quality?
Very interesting post. I wonder what is the glycated percentage in the average milk that can be bought in the supermarket?
or long-life milk (lang houdbare melk)
That’s a good question. I found in German wikipedia that 120 °C is the temperature when glycation starts. On the other hand, “Ultra-high temperature processing (UHT), ultra-heat treatment, or ultra-pasteurization[1] is a food processing technology that sterilizes liquid food by heating it above 135 °C (275 °F)”. Pasteurization, the processing of “normal” milk is below 100°C. In case of glycation i would say, stay away from long-life milk. What’s the last word from Master Trommelen?
When you have the option, I would stay away from long-life milk (I also think it’s less tasty). But long-life milk is not a bad product (glycation is still quite low). It’s ok to have some lying around in case you ever run out of normal milk. Glycation is more a concern in powder products that that also contain carbohydrate, such as weight-gainers or infant formulas.
Raw milk: 0%, pasteurized milk: 0-2%, UHT milk (houdbare melk): 0-10%. Glycation is more a concern with powder products, especially when powder products also contain carbohydrate.