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

Limited proteolysis of beta-lactoglobulin and beta-casein by pepsin was performed in the presence of varying concentrations of ethanol. beta-Lactoglobulin started to be cleaved by pepsin only in ethanol concentrations greater than 20%, when its secondary structure began to change. In 25% ethanol, the rate of hydrolysis of beta-lactoglobulin was slow (40% remained intact after 40 h of hydrolysis) and many short and hydrophilic peptides were observed. The rate of hydrolysis of beta-lactoglobulin reached its maximum in 30 and 35% ethanol (80% of beta-lactoglobulin was hydrolysed after 10 h), and a mixed population of hydrophilic and hydrophobic peptides of different lengths was observed. Large hydrophobic peptides appeared first, then some shorter products. The rate of hydrolysis of beta-lactoglobulin decreased at ethanol concentrations equal to or higher than 40%, when only a few long, hydrophobic peptides wee produced. As seen by circular dichroism, the addition of ethanol to beta-casein induced alpha-helix formation and reduced the rate of casein hydrolysis without changing the peptide profile. The only exception was the yield of a single peptide (Pro(81)-Met(93)).