Effect of gellan hydrocolloid on rheological properties and stabilization of a fiber-enriched Doogh

Doogh is a dairy drink which has attracted attention compared to the common drinks in use. By the application of dietary fibers، Doogh''s nutritional value will increase and the daily fiber intake requirements can be provided. The aim of the present study was to produce a stable and fiber-enriched Doogh by using gellan gum and a wheat fiber. Pasteurized and non-pasteurized Doogh samples containing gellan (0. 03% w/w) and fiber (0. 4 and 0. 8% w/w) were made and then stored at 4°C. Rheological properties، particle size distribution، phase separation and sensory attributes of the samples were analyzed. Pasteurized Dooghs containing fiber and gellan had higher shear stresses and viscosities in a constant shear rate compared to the non-pasteurized samples. The rheological properties changed from the Newtonian fluid in the control samples (without fiber and gellan) to the shear-thinning liquid (pseudo-plastic) fluid in the samples with fiber and gellan. The flow behavior index for pasteurized and non-pasteurized control samples was near one، while for the samples containing fiber and gellan (pasteurized and non-pasteurized) was less than one. Pasteurization of the samples containing fiber and gellan، in a constant fiber concentration، increased the consistency coefficient، apparent viscosity and yield stress and decreased the flow behavior index. The application of the fiber and gellan increased particle size of the samples. Moreover، the samples containing fiber and gellan were stable during storage; however، about 55% phase separation occurred in the control samples. By taking the quality indexes into account، the results showed that the best sample was the pasteurized Doogh containing gellan and fiber with the concentration of 0. 4%.