SOLUBILITY AND EMULSIFYING PROPERTIES OF BETACASEIN MODIFIED ENZYMATICALLY BY TRYPSIN

Abstract

Beta A1-casein was treated with TPCK-trypsin to give 3.2, 5.0, 5.8 and 7.4% hydrolysis of the peptide bonds. By sodium dodecyl sulfate-polyacrylamide gel electrophoresis the resulting peptides had apparent molecular weights in the range 8,000–4,000. Size-exclusion chromatography of hydrolyzed samples showed four major peaks near 15,000, 5,500, 3,500 and 2,500 molecular weights, representing 17, 15, 7 and 14% of the material, respectively, after 3.2% hydrolysis and 9, 6, 14 and 52% of the material, respectively, after 7.4% hydrolysis. Between the extremes 3.2% and 7.4% hydrolysis, a peak near 8,500 molecular weight was present until 5.8% hydrolysis then disappeared after 7.4% hydrolysis to be replaced by a peak near 12,000 molecular weight. Peptides recovered from reversed-phase high performance liquid chromatography were analyzed by determination of their amino acid composition and identified in the sequence of β-casein. After trypsin treatment, the solubility of β-casein hydrolysates was largely increased at pH 4.0–7.5. The emulsifying activity of the hydrolysates was higher than that of β-casein in the range of pH 1.5–3.5 and 6.5–10.0, but all the emulsions obtained with trypsin-treated β-casein were less stable than those obtained with original β-casein.