Interactions between β-Lactoglobulin and Pectins during in Vitro Gastric Hydrolysis

This paper deals with the influence of different levels of three pectins, low-methylated pectin (LMP), high-methylated pectin (HMP), and low-methylated and amidated pectin (LMA), on the in vitro gastric hydrolysis of β-lactoglobulin (β-lg). Proteolysis by pepsin consisted of a 2-h progressive reduction of pH. A turbidity measurement of β-lg−pectin mixtures was carried out during the proteolysis. The influence of pectins on pepsin enzymatic activity was also evaluated. β-Lg was resistant to peptic digestion. The presence of each of the three pectins at a concentration of 50 wt % increased the N release at all pH values considered, despite a significant inhibition of the pepsin enzymatic activity with the pectins. The turbidity of β-lg solutions during proteolysis was reduced by the addition of pectins, because of the formation of electrostatic complexes between this protein and pectins. The increase of N release could be a false positive result due to the difficulty of precipitating protein by trichloroacetic acid because of the formation of electrostatic complexes demonstrated by the decrease of turbidity. Keywords: β-Lactoglobulin; pectin; pepsin; N release; turbidity; pepsin enzymatic activity