EFFECT OF ACTINIDIN ON THE SOLUBILITY AND SDS-PAGE PATTERN OF SOYMILK PROTEINS

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The purpose of this investigation was to study the effect of actinidin, the proteolytic enzyme from kiwi fruit, on protein solubility (nitrogen solubility index, NSI) and sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE pattern of soymilk proteins. Actinidin from kiwi fruit was purified to homogeneity by precipitation with salt at pH 5.5 followed by anion exchange chromatography on a diethyl amino ethyl-Sephadex column. Actinidin significantly (P < 0.05) increased NSI of soymilk in a dose-dependent manner. A 40% increase in NSI was obtained when 0.8 unit of actinidin/mL soymilk was used. Higher level of enzyme resulted in a decrease in the NSI and formation of a gel-like structure. SDS-PAGE results showed increase in the intensity of several protein bands with molecular weights in the range of 16–20 kDa and 30–42 kDa in actinidin-treated soymilk. The results of this study indicate that higher solubility of soymilk proteins can be achieved by limited proteolysis using actinidin. Since solubility is a major quality attribute, actinidin can be used to improve the functionality of soymilk and extend the applicability of soymilk as an ingredient in other food products. PRACTICAL APPLICATIONS In this study, the effect of application of proteolytic enzyme actinidin from kiwi fruit in solubilization of soymilk proteins was confirmed. Since nutritional and functional properties of proteins usually require a protein with a relatively high degree of water solubility, the results of this study shows that actinidin can be used to improve nutritional attributes as well as the functionality of soymilk (such as emulsifying property, water-holding capacity, etc.) in different foods.