Utilization of laboratory-produced xanthan gum in the manufacture of yogurt and soy yogurt

The effect of laboratory-produced xanthan gum and mixtures of it with other gums at different concentrations on the chemical, microbiological, theological, micro-structural and sensory properties of yogurt and soy yogurt were studied. The addition of xanthan gum or its mixtures had no marked effect on pH-values, contents of total solids or the changes of lactic acid bacterial counts of yogurt and soy yogurt samples when fresh or during storage. In addition, mould and yeasts as well as coliform groups were not detected with any treatments, either when fresh or during storage. The viscosity values of cows' milk yogurt or soy milk yogurt during the fermentation period were affected by the type and concentration of stabilizer used. These values increased markedly using gum either singly or in combination with other gums. The use of xanthan gum or its mixtures at tested concentrations increased the curd tension of milk yogurt. Yogurt samples with xanthan gum at a concentration of 0.01% exhibited the highest curd tension values when fresh and at the end of storage period, while the addition of xanthan gum or its mixtures had variable effects on the curd tension of soy milk yogurt. The susceptibility to syneresis of yogurt samples decreased with the addition of xanthan gum or its mixtures, while no syneresis was detected in any fresh soy yogurt samples. Soy yogurt treated with 0.005% xanthan gum exhibited high resistance to syneresis during storage. The microstructures of yogurt with 0.01% and soy yogurt with 0.005% xanthan gum showed the smallest decreases in the dimensions of the pores, as well as the dimensions of the casein particles. Yogurt and soy yogurt treated with 0.01 and 0.005% xanthan gum respectively, gained the highest sensory scores compared to the corresponding other treatments.