Kinetic Studies on Protein Solubility and Electrophoretic Pattern of Soymilk Stored at Different Temperatures

In recent years soybean derived foods (such as soymilk) have received considerable attention due to their high nutritional value and functional properties. The purpose of this study was to investigate the changes in protein solubility and electrophoretic behavior of soymilk stored at refrigerator and freezer conditions. A 12% total solid content soymilk was produced and stored at 4 and -18ºC. At different time intervals samples were removed an analyzed for protein solubility and SDS-PAGE. A gradual decrease in solubility of proteins stored at -18ºC with time was observed such that after 3 weeks solubility was dropped from 75% to 45% (30% decrease) and remained at 41% thereafter up to 6 weeks. These changes appeared to follow a first order kinetics with a rate constant (k) of 0.014(day)-1 and half life (t1/2) of 62 days. Similar pattern was seen in the refrigerated sample except that the decrease in solubility occurred slowly and at final stage, solubility decreased by 17%. At this temperature the decrease in protein solubility followed a zero order kinetics with k of 0.625 (day)-1 and t1/2 of 144 days These results indicate that long term refrigeration and freezing of soymilk must be avoided.