Effect of the Yam Starch (<em>Dioscorea</em> spp.) and Pectin on the Rheological Properties of Stirred Yogurt

Abstract

The aim of study was to evaluate the effect of the temperature and concentration of yam starch and pectin on the rheological properties of yogurt. A stationary test was performed using an MCR 302 (Anton Paar) rheometer with concentric cylinder geometry, varying the strain gradient in an ascending (0-100/sec) and a descending (0-100/sec), at different temperatures (10, 20 and 30°C, respectively). Yogurts were made using two varieties of yam starch (“Espino” and “Criollo”) and different concentrations of yam starches (0.1, 0.3 and 0.5% w/w, respectively) and pectin at 0.3% w/w was used as a commercial reference. The experimental data were fitted to the power law models, Herschel-Bulkley and Casson. The model that best represented the rheological data was the power law $(R^2≥0.977, MSE≤0.674)$. Yogurts with an addition of yam starch presented thixotropy and pseudoplastic behavior $(0 < n < 1 )$; However, when pectin was used at 30°C the behavior was dilating (n = 1.23). Yogurts with “Criollo” yam starch have higher consistency, while yogurt with an addition of “Espino” yam starch are more pseudoplastic and have less thixotropy.