Soy protein-xanthan gum interaction:stability and rheology

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Virginia Polytechnic Institute and State University

This study investigated the effects of ionic strength, pH, gum concentration, and protein type on protein - xanthan gum interactions. Commercial soy sauce and tamari sauce as well as model systems of soy protein isolate and whey protein concentrate were the sources of protein used for evaluation with xanthan gum.

Preliminary research indicated that when either soy sauce or tamari sauce were mixed with xanthan gum, stable solutions with notable viscosity synergisms resulted. The soy protein and whey protein systems were subsequently prepared with a range of 0 to 5% added sodium chloride. Results indicated that an equilibrium existed between proteins and xanthan gum such that increased sodium chloride initially increased solution stability; but when in excess, the sodium chloride led to a loss of protein - xanthan gum solution solubility and in some cases to precipitation. Precipitation was also noted at the pH extremes of 2,3, and 9 and when xanthan gum was present in excess, or at 0.25%.

The effects of sodium chloride, protein type, and pH on the rheological parameters of model solutions were also examined. Higher sodium chloride levels yielded greater viscosity synergisms. Those solutions made.with intact protein were generally higher in apparent viscosity than similar solutions made with hydrolyzed protein. Solutions at pH 5 were generally higher in viscosity than were similar solutions at pH 7.

Several factors that appeared to affect the stability, solubility, and the rheological parameters of protein - xanthan gum solutions were sodium chloride concentration, gum concentration, pH, and protein type.