HOW TO INCREASE BETA-LACTOGLOBULIN SUSCEPTIBILITY TO PEPTIC HYDROLYSIS

Since beta-lactoglobulin is resistant to peptic hydrolysis in physiolo gical conditions, the increase of its digestibility by this enzyme was sought by the destabilization of its folding using methods that do no t influence the biological value of protein, such as high pressure, me dium polarity changes (alcohol addition), and esterification (ethylati on). For example, the rate of hydrolysis of beta-lactoglobulin by peps in (negligible at 0.1 MPa) increased considerably with pressure up to 300 MPa. The susceptibility of all potential beta-lactoglobulin proteo lytic sites to peptic cleavage remained constant over the pressure ran ge that was studied. The addition of alcohols decreases the bulk diele ctric constant of the medium and, according to CD measurements, increa ses significantly the proportion of helical structure in beta-lactoglo bulin while increasing susceptibility to peptic hydrolysis. In the pre sence of alcohols (ethanol, ethylene glycol), beta-lactoglobulin hydro lysis by pepsin was initiated when its secondary structure began to ch ange and diversified peptic peptide populations were obtained. The che mical modification of beta-lactoglobulin by mild esterification yields a 40%-ethylated beta-lactoglobulin derivative that is rapidly hydroly zed by pepsin. As compared with peptic hydrolysis of beta-lactoglobuli n in aqueous ethanol, 22 new sites of pepsin cleavage were induced by esterification of the protein.