Abstract: This study was aimed to explore the properties of soluble aggregates from whey protein isolate (WPI) modified with mixed chymotrypsin and transglutaminase (TGase) using electrophoresis, a fluorescence spectrophotometer and a rotational rheometer. The results showed that the viscosity of protein aggregates modified by mixed enzymes was higher, and the content of free sulfhydryl groups was significantly decreased; however, the surface hydrophobicity and ζ-potential did not change significantly when compared with single TGase modification. The average particle size of mixed enzyme-modified aggregates was (153.66 ± 9.15) μm, while that of TGase-modified aggregates was (157.92 ± 10.91) μm, suggesting no significant difference. Comparative analysis using SDS-PAGE and Native-PAGE showed that single TGase-modified aggregates had higher molecular weight, and was trapped at the injection port; in contrast, the molecular weight of aggregates modified by mixed enzymes was moderate, mostly distributed around 65 kD, which was coincided with the particle size distribution. The surface of aggregates modified by both enzymes showed a corrugated shape with structural uniformity. The solubility curve of mixed enzyme-modified WPI aggregates in the range of pH 2.0–7.0 was gentle, while the solubility was increased at pH 4.0–5.0 when compared with the unmodified whey protein. The results in this study may provide a theoretical basis and technical reference for applying enzymatically modified WPI in yogurt and fermented dairy beverage.

Key words: whey protein, soluble aggregates, chymotrypsin, transglutaminase(TGase)