Effect of pH and heat treatment of cheese whey on solubility and emulsifying properties of whey protein concentrate produced by ultrafiltration

The effects of pH and heat treatment of cheese whey on protein solubility (PS) at pH 4.6 and on emulsifying properties of whey protein concentrate (WPC) were studied by response surface methodology (RSM). PS followed a quadratic relationship with pH and a linear relationship with heat treatment. Highest values for PS were found between pH 6.0 and 6.6 with heat treatment at 68 degrees C for 2 min. and maximum solubility was reached at pH 6.3. Heat treatment strongly decreased protein solubility throughout the entire pH range. The emulsifying properties were notably benefited by raising the pH from 6 to 7, best values being shown at pH 7 with a heat treatment of 70 degrees C for 2 min. The effect of heat treatment on the emulsifying properties was dependent on the pH level. At about pH 7, the heat treatment adversely affected the emulsifying properties, probably due to excessive protein denaturation. (C) 2004 Elsevier Ltd. All rights reserved.