The effects of enzymatic hydrolysis of casein on apparent yield stress and some emulsion properties

In this investigation, casein was proteolysed at different levels using a neutral proteinase (Neutrase) and the effects of proteolysis on emulsion capacity (EC) of casein, emulsion stability (ES), emulsion density (ED), and apparent yield stress (AYS) values of emulsions have been investigated. In order to clarify the effect of proteolysis on proteins, the proteolysis-applied proteins at different levels went through urea-PAGE and SDS-PAGE analysis. The proteolysis level exerted a statistically very significant difference on proteolysis degree, EC, ES, ED, AYS values (p < 0.01). In the trial, no significant effect of enzyme and enzyme inhibitor (ethylenediaminetetraacetic acid, EDTA) on parameters was determined (P > 0.05); the difference was found to be associated with an outcome from proteolysis. While proteolysis increased rapidly up to 20th minute, it increased slowly from 80 min. It was also observed that urea-PAGE and SDS-PAGE patterns belonging to casein fractions were quite in perfect harmony with proteolysis degrees, whereas a remarkable weakening in main protein bands due to the period was seen. A constitution of new peptide bands was observed up to 80 min, but these bands vanished after this period. Another finding, which became the chief focus of our concern throughout our experimental trials was that EC, ES, ED and AYS values generally improved up to 5 min; however, it did not change from that period up to 20 min. From that period, these values were negatively affected, whereas from 80 min (0.136 AN/TN) a remarkable deterioration was observed in emulsion properties. (c) 2005 Elsevier Ltd. All rights reserved.