Effects of heat treatment and pectin addition on β-lactoglobulin allergenicity

The specific effects of heat treatment and/or addition of low/high-methylated pectin (LMP/HMP) on the allergenicity of β-lactoglobulin (β-Lg) and its hydrolysis products were investigated through a two-step in vitro digestion approach. β-Lg was first hydrolyzed by pepsin and then by a trypsin/chymotrypsin (T/C) mixture done in a dialysis bag with a molecular weight cutoff of 1000. The protein digestion was followed by SDS-PAGE electrophoresis performed on each digestion product, and their in vitro allergenicity was analyzed by immunoblotting. Such procedure was applied on β-Lg samples mixed with the two kinds of pectin before or after heating (80°C, 25 min) to determine the respective impact of heat treatment and pectin addition. Heat denaturation improved significantly the susceptibility of β-Lg against the pepsin and the T/C. This effect, which was coupled to a reduction in immunoreactivity of the digested β-Lg, appeared to be distinctively modulated by LMP and HMP. Through nonspecific interaction with the β-Lg, pectin could reduce the accessibility of cleavage sites and/or epitope sequences. This mechanism of action is discussed in relation to the intra- and intermolecular interactions between β-Lg and pectin initiated under the experimental conditions. © 2006 American Chemical Society.