59D-11

Proteins are surface-active biopolymers that are extensively used in the food industry as emulsifiers to manufacture products such as desserts, spreads or whipped cream. Sugar is often added to increase the sweetness of these products. Recent investigations have shown that the addition of sugar can influence functional properties of proteins such as gelation. However, no experiments have been conducted that investigated the influence of sugars on the emulsifying properties of proteins.

The objective of this study was to investigate the influence of sugars on the surface activity of bovine serum albumin solutions.

All chemicals were purchased from Sigma Chemical Co., MO. BSA solutions (5, 2, 1, 0.5, 0.1wt%) were prepared using distilled and deionized water. Fructose, Glucose and Sucrose were added to solutions at concentrations ranging from 0 to 40wt%. The surface activity of protein solutions containing various amounts of sugars was measured using a drop shape analysis tensiometer (Kruess USA, Charlotte, NC)

The equilibrium surface tension of pure sugar solutions decreased from 72 mN/m to approximately 65 mN/m as the sugar concentration was increased from 0 to 40wt% and depended on the type of sugar that was used (Sucrose > Glucose, Fructose). The adsorption kinetics of proteins at the air-water interface depended strongly on the concentration of proteins used (i.e. full coverage was reached within 20 minutes for 5 wt% BSA solutions compared to 3 hours for 0.1wt%). Rates of adsorption were significantly altered upon the addition of sugars, i.e. pure BSA solution (5wt%) adsorbed nearly twice as fast as BSA solution containing 40wt% sucrose. The results were explained in terms of a novel molecular depletion flocculation theory.

The results have important implications for food manufacturers as they explain the differences in protein functionality that have been encountered upon the addition of cosolvents such as sugars.