Effect of Heat Treatment on the Property, Structure, and Aggregation of Skim Milk Proteins.

Hongbo Li,Jinghua Yu,Hongjuan Li,Tingting Zhao

doi:10.3389/fnut.2021.714869

Abstract

To study the mechanism of heat-induced protein aggregates, skim milk was heated at 55, 65, 75, 85, and 95°C for 30 s. Then, the sulfhydryl content, surface hydrophobicity, and secondary structure of heat-treated skim milk were studied. Treating skim milk at different temperatures induced a decrease in sulfhydryl content (75.9% at 95°C) and an increase in surface hydrophobicity (44% at 95°C) with a disrupted secondary structure containing random coil, β-sheet, and β-turn of skim milk proteins. The change in these properties facilitated aggregate formation through disulfide bonds and hydrophobicity interaction. Microstructural observation also showed a higher degree of aggregation when skim milk was heated at 85 and 95°C. The result of two-dimensional polyacrylamide gel electrophoresis demonstrated that the aggregates consisted of a high proportion of κ-casein, β-lactoglobulin, and other whey proteins.

Highlights

Milk derived from domesticated mammalian animals has a long history of being a part of the human diet
The goal of this study is to explore the mechanism of heat-induced protein aggregates after heat treatment on skim milk, and the interaction of different denatured milk proteins
The results showed that heat treatment increased the surface hydrophobicity of whey protein isolate and decreased the surface hydrophobicity of bovine serum albumin (BSA), and that the treatment had a little effect on casein

Summary

Introduction

Milk derived from domesticated mammalian animals has a long history of being a part of the human diet. In the processing of these dairy products, heat treatment is an essential step to reduce the potential risk of survival of pathogenic microorganisms and extend the shelf life of final products. It can improve the functional properties of some specific dairy products, such as yogurt and cheese [2, 3]. Heat treatment has a significant effect on the protein network of dairy product [4]. It is well-known that heat-treated milk can form a gel network with better strength and firmness in a shorter time [5]. The application of heat leads to different reactions among milk proteins, contributing to the denaturation and/or aggregation of whey proteins and formation of complexes between caseins and whey proteins [6,7,8,9]

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