Abstract
It is important to evaluate the nutritional quality of milk during the shelf-life, especially during home storage, from a consumer viewpoint. In this study, we investigated the impact of pasteurization (85 °C/15 s) and subsequent storage (at 4 °C for 7 days) on the coagulation behavior of milk and protein digestibility in a dynamic in vitro gastric digestion test. A high level of hydration in curd formed in pasteurized milk upon 7-day cold storage compared to raw and pasteurized milk, indicating fast pepsin diffusion in the interior of curds, increasing the hydrolysis rate. The digesta collected at various time points throughout the gastric digestion were studied using o-phthaldialdehyde (OPA), sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), liquid chromatography tandem mass spectrometry (LC-MS/MS), and amino acid analysis. These results showed that milk proteins were hydrolyzed quickly upon a long period of cold storage. Additionally, qualitative and quantitative results obtained using LC-MS/MS exhibited significant differences between samples, especially in pasteurized milk upon cold storage. Processing and storage played a decisive role in bioactive peptide generation. Such knowledge could provide insights into and directions for the storage of pasteurized milk for further clinical studies on protein bioavailability and the generation of bioactive peptides for desired health outcomes.
Highlights
Milk proteins, as an important aspect of dietary proteins for humans, have a good nutritional value: They have a high content of several essential amino acids and good digestibility [1]
There was no significant difference in the pH profiles between pasteurized milk and raw milk, but a slower decrease in the pH was observed in pasteurized milk during storage
A slow decrease in pH observed in pasteurized milk upon 7 days of storage indicated that a curd which could exert a greater buffer capacity was formed and slowed down the decrease in pH
Summary
As an important aspect of dietary proteins for humans, have a good nutritional value: They have a high content of several essential amino acids and good digestibility [1]. Milk proteins have recently attracted an increasing amount of attention, since they contain bioactive peptides which can be released during gastrointestinal digestion [2]. Heat treatment above 60 ◦ C leads to β-Lg denaturation, aggregation, and the association of denatured β-Lg with casein micelles through interactions with κ-casein [4]. These structural changes at the molecular level can lead to changes in the physicochemical properties of milk (viscosity, surface hydrophobicity, rheological property, etc.) [5,6,7].
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