Abstract
The goal of this study was to determine the impact of industrial processes on the digestion of six milk protein matrices using the harmonized INFOGEST in vitro static digestion protocol. First, this method was optimized to simple protein matrices using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and size exclusion chromatography (SEC) to compare the intestinal protein hydrolysis obtained with increasing quantities of pancreatin. Similar results were achieved with the originally required pancreatin amount (trypsin activity of 100 U.mL−1) and with a quantity of pancreatin equivalent to a trypsin activity of 27.3 U.mL−1, which was thus used to perform the in vitro digestion of the milk matrices. Molecular weight profiles, peptide heterogeneity from LC-MS/MS data, calcium, free amino acid, and peptide concentrations were determined in the gastric and intestinal phases to compare the milk protein digests. Results showed that the industrial process affected not only the protein distribution of the matrices but also most likely the protein structures. Indeed, differences arose in terms of peptide populations generated when the caseins were reticulated or when their calcium concentrations were reduced.
Highlights
Milk proteins have been widely used in the food industry for the past 50 years due to the wide array of functions that they exhibit as food ingredients
The optimization of the static in vitro digestion for dairy protein was performed with the whey protein isolate (W matrix) as whey proteins are more resistant to gastrointestinal enzymes [18]
This study first demonstrated that, the INFOGEST protocol is the method of choice when simulating static in vitro digestion, some adjustments can still be necessary when trying to resolve certain research questions, in this case, the quantity of pancreatin needed to be optimized in order to better adapt it to our simple milk protein matrices
Summary
Milk proteins have been widely used in the food industry for the past 50 years due to the wide array of functions that they exhibit as food ingredients. Milk proteins are known for their nutritional value and for their physicochemical and physiological properties [1]. Bovine milk proteins can be differentiated into two categories: micellar caseins and native whey proteins. Caseins are flexible phosphorylated proteins that are distinguished into four classes known as α-S1 α-S2 , β-, and κ-caseins, which interact together to form a micelle. The structure of the casein micelle has been a subject of debates for years, and while no consensus has been agreed upon, two models are currently widespread: the submicellar and the nanocluster models [2]. The submicellar hypothesis formulates that the proteins in sodium caseinates, which characterize the protein extracts after removal
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