HYDROPHOBICITY, SOLUBILITY, AND EMULSIFYING PROPERTIES OF SOY PROTEIN-PEPTIDES PREPARED BY PAPAIN MODIFICATION AND ULTRAFILTRATION

Peptide size control is important for obtaining desirable functional p roperties so that these peptides can be better utilized. Proteolytic e nzymatic modification of soy protein isolates (SPI), followed by ultra filtration, is an effective way to fractionate these proteins into pep tides with controlled molecular size. SPI was predenatured by mild alk ali at pH 10 and heated at 50 degrees C for 1 h prior to partial hydro lysis by papain at pH 7.0 and 38 degrees C for 10, 30, and 60 min (PMS PI10, PMSPI30, and PMSPI60). The hydrolysate PMSPI60 was further fract ionated by ultrafiltration wish a stirred cell and disc membranes (100 -, 50-, and 20-kDa molecular weight cut-off) into one retentate (R100) and three permeates (P100, P50, and P20). Molecular weighs distributi on, surface hydrophobicity (S-0), protein solubility (PS), emulsifying activity index (EAI), and emulsion stability index (ESI) of the contr ol SPI (without added papain), hydrolysates, and ultrafiltrates were i nvestigated. Significant increases (P < 0.001) in S-0, PS, EAI, and ES I were observed in the hydrolysates. Peptides in the permeates had hig her PS and EAI but lower So than the peptides in the retentate and hyd rolysate. Soy protein peptides that were prepared from SPI by papain m odification and ultrafiltration had lower molecular weight, higher sol ubility, and higher emulsifying properties. They could find use in pro ducts that require these properties, especially in the cosmetic and he alth food industries.