Thermal effects on the conformation and susceptibility of beta-lactoglobulin to hydrolysis by gastric and pancreatic endoproteinases

The thermal stability and susceptibility of a β-lactoglobulin (β-lg) enriched protein fraction to hydrolysis by gastric and pancreatic proteinases was studied using differential scanning calorimetry (DSC). Pepsin, trypsin, chymotrypsin, elastase, combinations of trypsin and pepsin and the commercially available enzyme preparations, Corolase PP and PTN 3.0S, were used for hydrolysis. DSC thermograms showed that the β-lg fraction had a higher thermal/structural stability at pH 3.0 than at pH 8.0. Holding the β-lg fraction at 50 °C for 120 min at pH 3.0 or pH 8.0 decreased the structural stability of the protein. DSC analysis showed that heat treatment of β-lg at 80 °C for 20 min resulted in complete destruction of tertiary structure. The low levels of hydrolysis of β-lg obtained by pepsin at pH 3.0 may be attributed in part to greater structural and thermal stability of the protein at this pH. Heat treatment (80 °C for 20 min) increased the susceptibility of the β-lg fraction to enzymatic hydrolysis by pepsin and trypsin. The order of addition of enzyme influenced hydrolysis; pepsin followed by trypsin resulted in greater hydrolysis than trypsin followed by pepsin. This study confirmed the utility of DSC analysis in conjunction with enzymatic hydrolysis as a means of studying the structural stability of β-lg.