The Influence of Whey Protein Heating Parameters on Their Susceptibility to Digestive Enzymes and the Antidiabetic Activity of Hydrolysates

Abstract

The inhibition of dipeptidyl peptidase-IV (DPP-IV) and the release of glucagon-like peptide-1 (GLP-1) could normalize blood glucose levels in diabetic patients. This study evaluated the susceptibility of whey proteins to enzyme hydrolysis and the antidiabetic properties of protein hydrolysates from β-lactoglobulin (β-LG) and α-lactalbumin (α-LA) solutions compared with whey protein isolate (WPI) solution treated at different heating temperatures (65, 75, and 85 °C). α-LA hydrolysate provided the lowest degree of hydrolysis (DH). Those heating temperatures did not significantly affect the DH of all protein hydrolysates. α-LA hydrolysate significantly increased GLP-1 levels and DPP-IV inhibitory activity more than β-LG hydrolysate. WPI hydrolysate inhibited DPP-IV activity less than an α-LA hydrolysate, but they were no significant differences for GLP-1 release activity. Heat treatment could affect the antidiabetic properties of all protein hydrolysates. Heating at 75 °C resulted in greater inhibition of the activity of DPP-IV than at 65 and 85 °C. The highest increase in GLP-1 release was also observed by heating at 75 °C. The recently obtained information is useful for the utilization of α-LA, heated at 75 °C for 30 min, in the preparation of antidiabetic food supplements.

Keywords: antidiabetic; heat treatment; whey protein; α-lactalbumin; β-lactoglobulin.

Figure 1

Degree of hydrolysis (DH, %) of protein hydrolysates: (a) Comparisons between different types of protein solutions (WPI, β-LG, and α-LA), and (b) comparisons between different heat treatment temperatures (65, 75, and 85 °C) for 30 min for all protein solutions. Data are presented as mean ± standard deviation (n = 3). The different letters ^A,B indicate a significant difference at p < 0.05. The letter ^ns indicates no significant difference at p ≥ 0.05. WPI, β-LG, and α-LA denote whey protein isolate, β-lactoglobulin, and α-lactalbumin, respectively.

Figure 2

Cell viability (%) of the human salivary gland (HSG) cells after 24 h incubation with DMEM (control) and the protein hydrolysate at concentrations between 0.078 and 10 mg/mL (n = 4). WPI, LG, and LA denote whey protein isolate, β-lactoglobulin, and α-lactalbumin solutions, respectively. The number after the abbreviated protein solutions indicates the temperature (°C) of the heat treatment process.

Figure 3

Dipeptidyl peptidase-IV (DPP-IV) inhibition values (%) of protein hydrolysates at a concentration of 0.313 mg/mL: (a) Comparisons between different types of protein hydrolysates from WPI, β-LG, and α-LA solutions; (b) comparisons between different heat treatment temperatures (65, 75, and 85 °C) for 30 min for all protein hydrolysates. Data are presented as mean ± standard deviation (n = 3). The different letters ^A,B indicate a significant difference at p < 0.05. WPI, β-LG, and α-LA denote whey protein isolate, β-lactoglobulin, and α-lactalbumin, respectively.

Figure 4

Bi-plot for the protein hydrolysates and their properties from principal component analysis (PCA). WPI, LG, and LA denote whey protein isolate, β-lactoglobulin, and α-lactalbumin solutions, respectively. The number after the abbreviated protein solutions indicate the temperature (°C) of the heat treatment process.