Milk protein coagulation under gastric conditions: A review

Summary of a review by Huppertz & Chia 2020

Proteins play an important role in many processes in the body. For dietary proteins to be utilized efficiently, the protein needs to be digested to free amino acids and di- and tripeptides in the intestine. Several factors and processes can affect protein digestibility, with one of them being gastric coagulation. This summary outlines the review from Huppertz & Chia on gastric coagulation of milk proteins and how this can affect milk protein digestibility.

The review distinguishes three classes of proteins in milk: caseins, whey proteins and milk fat globule membrane proteins. The latter class only represents a small portion of the total milk protein (1-2%), whereas caseins and whey proteins dominate the milk proteins quantitatively. It reveals that these milk proteins behave differently during gastric coagulation and this is affected by processing factors (like heat treatment and homogenization).

Physiological relevance of gastric coagulation

The authors get into how gastric coagulation of milk proteins influences the transit of dietary protein through the stomach, resulting in a more sustained release of amino acids in the bloodstream potentially leading to increased utilization of protein.

It is explained that during gastric coagulation, the so-called curds that are formed can differ in terms of firmness, which can affect digestion. The authors put forward that consumption by infants of soft-curd milk has shown reduced digestive difficulties (such as less occurrence of regurgitation) compared with consumption of hard-curd milk. Different factors are mentioned that can determine whether milk protein will form hard or soft curds in the stomach, for instance milk composition, cow breed and processing of milk.

Impact of processing on gastric coagulation

Two processing steps are pointed out that influence the gastric coagulation of milk: heat treatment and homogenization. For heat treatment, the effects on gastric coagulation are reported to be largely related to the denaturation of whey proteins, whereas for homogenization, the effects are primarily related to changes in milk fat globules. The authors present that both heat treatment and homogenization have been shown to result in the formation of softer curds, and suggested that this can possibly improve digestibility.

The authors noticed, however, that while heat treatment leads to so-called soft-curd milk, heat treatment may also affect protein digestion negatively: during heat treatment, protein glycation can occur which impacts digestibility and limits the uptake of the essential amino acid lysine.

Conclusion

This review paper concludes that gastric coagulation of milk protein regulates gastric emptying, resulting in a sustained supply and utilization of protein in the human body. It describes that heat treatment and homogenization of milk can affect gastric coagulation and may therewith also affect milk protein digestion.

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Reference

1. Huppertz, T., & Chia, L. W. (2020). Milk protein coagulation under gastric conditions: A review. International Dairy Journal, 104882