Emulsifying properties of wheat germ:Influence of pH and NaCl

Abstract

The emulsifying properties of wheat germ (WG) were evaluated as a function of WG concentration (1%, 2%, 4% and 8%, w/w), pH (3, 5, 7 and 10), NaCl content (0.5%, 1%, 3% and 5%, w/w) and heat treatment (20 min at 100 °C). Droplet size, emulsifying activity, zeta-potential, creaming stability and apparent viscosity were determined. Results indicated that emulsifying ability of WG emulsion is dependent on WG concentration and insensitive to pH changes. The volume-weighted average diameter (D[4,3]) of the emulsion droplet size gradually decreased with WG concentration, and the droplet size was the smallest at WG concentration of 4%. The dispersion of oil phase in aqueous medium was promoted by adding 0.1 g/L SDS solution, and the emulsion had the minimum droplet size. The droplet size (D[4,3]) of emulsions showed an increase of droplet size after heat treatment at any concentration. D[4,3] of WG emulsion increased first and then decreased with addition of NaCl, and reached the maximum at 3% of NaCl concentration. The emulsifying activity and zeta-potential of the emulsion distinctly reduced as NaCl increased. The pH has little effect on the emulsifying activity and droplet size of WG emulsion. The zeta-potential of emulsion was negatively charged regardless of the conditions. The emulsion has a satisfactory creaming stability when NaCl concentration exceeds 0.5% during the 10-day storage. The emulsion kept stable at pH 7, and showed instability under acidic or alkaline condition. Overall, WG can be used as a natural emulsifier, and the emulsifying properties of WG emulsion are highly sensitive to ionic strength.