Yam soluble fiber (YSF) extracted from Pachyrhizus erosus was added (1 g per 100 mL) to a stirred yogurt (SY(YSF)). Its syneresis and microstructure properties were evaluated and compared to those of a stirred yogurt (SY(C)) without added YSF. The SY(C) yogurt exhibited a more compact casein micelle aggregates network than that of the SY(YSF) yogurt which was more open, relaxed and covered with fibrous structures attributed to the YSF components. The rheological analysis showed that the SY(YSF) yogurt had lower storage modulus (G') and loss modulus (G '') values in the linear viscoelastic region than the SY(C) yogurt, but its flow behavior was characterized by a lower flow index (n), higher consistency index (k), and higher yield stress (tau(0)) than the SY(C) yogurt. Incorporation of the YSF reduced significantly the syneresis and produced a more acceptable mouthfeel in the SY(YSF) yogurt in comparison to the SY(C) yogurt, indicating the viability of the process to obtain a commercial product. (c) 2010 Elsevier Ltd. All rights reserved.