Improved Water Resistance of Soy Protein Adhesive at Isoelectric Point

摘要

Our objective was to study the effects of protein surface charge on the adhesive performance of soy protein isolates (SPI). We used laboratory-prepared, freeze-dried SPI and achieved positive, neutral, and negative net charges on the surface of protein bodies by adjusting the pH. We evaluated adhesive performance as indicated by bond strength and water resistance, thermal denaturation, and rheological properties. Results indicated that a neutral surface charge of protein at isoelectric point (pI) was critical in increasing water resistance of SPI. The highest wet strength of SPI was reached at pI. Dry and soaked strengths were high in the pH range of 3.6 to 7.6. Differential scanning calorimetry results showed that SPI were more thermally stable at pI than at other pH values. Soy protein became insoluble at pI; we used xanthan gum, dextrin D2006, dextrin D2256, and pectin as suspension additives to increase homogeneity of the adhesive at pI. Xanthan gum solution had the highest viscosity among the four suspensions. Addition of xanthan gum could mimic the rheological properties of SPI at the expense of adhesion strength