Addition of Cyperus esculentus (tiger nut) milk improved the flavor and gelation properties of set yogurt: The main contribution of volatile constituents, starch and proteins

The modification effects of Cyperus esculentus milk (CEM) on the sensory and gel properties of set yogurt were elucidated in this study. It was found that a suitable CEM addition adjusted the color, moderated the acidity, and enriched the aroma of compound yogurt. Interestingly, the internal network structures of yogurt gel were strengthened at a low CEM addition, causing the improvement of yogurt textural properties, viscoelasticity and water-holding-capacity. However, a high CEM addition induced the incompact gel structures, unbeneficial to the expected textures and rheology of compound yogurt. Then, starch (CES) and proteins (CEP) were isolated to elucidate their influence on the gelation behaviors of casein. The results showed that CES always promoted the formation of CES-casein gel, improving its textural, elastic and morphological characters. This resulted from the presence of branchy side chains of amylopectin and the viscosity of starch molecules, making CES tightly anchor with casein gel and thus fill in the gel pores. However, the CEP-casein gel properties described an enhanced-weakened trend with CEP addition increasing. Notably, at a low addition, CEP well-dispersed and interacted with casein, filling into gel pores and thus strengthening gel network, while at a high addition, the self-gelling CEP gradually separated from casein gel due to few branchy structures and insufficient viscosity. It was the characteristic behaviors of CEM components that affected the gelling properties of compound yogurt. Conclusively, a moderate addition of CEM (<20%) is recommended to enrich the flavor of set yogurt with simultaneously-improved or maintained textural and gelling properties.