PROTEOLYSIS OF BETA-LACTOGLOBULIN AND BETA-CASEIN BY PEPSIN IN ETHANOLIC MEDIA

Limited proteolysis of beta-lactoglobulin and beta-casein by pepsin wa s performed in the presence of varying concentrations of ethanol. beta -Lactoglobulin started to be cleaved by pepsin only in ethanol concent rations greater than 20%, when its secondary structure began to change . In 25% ethanol, the rate of hydrolysis of beta-lactoglobulin was slo w (40% remained intact after 40 h of hydrolysis) and many short and hy drophilic peptides were observed. The rate of hydrolysis of beta-lacto globulin reached its maximum in 30 and 35% ethanol (80% of beta-lactog lobulin was hydrolysed after 10 h), and a mixed population of hydrophi lic and hydrophobic peptides of different lengths was observed. Large hydrophobic peptides appeared first, then some shorter products. The r ate of hydrolysis of beta-lactoglobulin decreased at ethanol concentra tions equal to or higher than 40%, when only a few long, hydrophobic p eptides wee produced. As seen by circular dichroism, the addition of e thanol to beta-casein induced alpha-helix formation and reduced the ra te of casein hydrolysis without changing the peptide profile. The only exception was the yield of a single peptide (Pro(81)-Met(93)).