How to increase beta-lactoglobulin susceptibility to peptic hydrolysis

Since beta-lactoglobulin is resistant to peptic hydrolysis in physiological conditions, the increase of its digestibility by this enzyme was sought by the destabilization of its folding using methods that do not influence the biological value of protein, such as high pressure, medium polarity changes (alcohol addition), and esterification (ethylation). For example, the rate of hydrolysis of beta-lactoglobulin by pepsin (negligible at 0.1 MPa) increased considerably with pressure up to 300 MPa. The susceptibility of all potential beta-lactoglobulin proteolytic sites to peptic cleavage remained constant over the pressure range that was studied. The addition of alcohols decreases the bulk dielectric constant of the medium and, according to CD measurements, increases significantly the proportion of helical structure in beta-lactoglobulin while increasing susceptibility to peptic hydrolysis. In the presence of alcohols (ethanol, ethylene glycol), beta-lactoglobulin hydrolysis by pepsin was initiated when its secondary structure began to change and diversified peptic peptide populations were obtained. The chemical modification of beta-lactoglobulin by mild esterification yields a 40%-ethylated beta-lactoglobulin derivative that is rapidly hydrolyzed by pepsin. As compared with peptic hydrolysis of beta-lactoglobulin in aqueous ethanol, 22 new sites of pepsin cleavage were induced by esterification of the protein.