Emulsifying properties of peptides from the hydrolysis of caseins and whey proteins

hey protein isolate and casein were hydrolyzed to 5% degree of hydrolysis by Alcalase, chymotrypsin, Neutrase or trypsin. The hydrolysates were fractionated by ultrafiltration (10,000 molecular weight cut-off) and freeze-dried. Hydrolysis by each enzyme yielded four fractions--hydrolysate, retentate, permeate and control; whose emulsifying properties were evaluated by a turbidimetric method.;Hydrolysis of whey proteins by all four enzymes studied, decreased the emulsifying activity index and emulsion rating. None of the permeate fractions from whey protein isolate formed stable emulsions. Hydrolysis of casein by Alcalase and Neutrase decreased its emulsifying activity while hydrolysis by chymotrypsin and trypsin improved it. The permeate fractions from these two enzymes showed high emulsifying activity index but poor emulsion rating. There was no consistent trend in change of emulsifying properties due to separation of low molecular weight peptides by ultrafiltration. The retentate fraction from tryptic hydrolysis of casein had superior emulsifying properties. Reverse-phase high performance liquid chromatography (RP-HPLC) analysis showed that this fraction had peptides eluting only at a high acetonitrile gradient and no polar peptides. Permeate fractions which had only early-eluting peaks did not form emulsions while fractions with peptides eluting across the gradient had intermediate emulsifying properties. No significant correlations were found between the oil-water interfacial tension and emulsion properties.;Peptides from the retentate fraction of tryptic hydrolysis of casein were separated by ammonium sulfate precipitation, ion exchange chromatography and RP-HPLC. The 30% ammonium sulfate precipitate and the fraction which eluted at a high ionic strength during anion exchange at pH 8.0 had superior emulsifying properties. Four peptides were purified by preparative RP-HPLC and characterized. Three of the four peptides were positively identified by amino acid sequencing and computational methods. The peptides identified were...