Evaluating effects of orange fiber on physicochemical, rheological and sensory properties of strawberry yogurt using Response Surface Methodology(RSM)

The aim of this study was to investigate the effects of adding orange fiber on physicochemical, rheological and sensory properties of strawberry yogurt using response surface method (RSM). The amount of fiber was in the range of 0-1.2% with the storage time of 3-29 days. The results showed that by increasing fiber amount, the viscosity and dry matter increased and the final product syneresis decreased significantly (P<0.05) but acidity and pH was not significantly affected (P>0.05). The amount of syneresis and acidity significantly increased during storage, but pH and viscosity decreased (P<0.05). Also, increasing the amount of fiber content increased yellowish spectrum (+b* parameter) while the rate of Lightness (L*) of the samples (P 0.05) decreased. Sensory evaluation results showed that by increasing of fiber amount, the score of color, odor, taste and overall acceptance decreased but the gained scores were at the good range and acceptable. According to the empirical models obtained by response surface methodology the relation between different variables were suitable. Finally, the optimum conditions for production of strawberry yogurt containing orange fiber were obtained using 1.2% fiber in a storage period of 16 days. The final product viscosity was 3519 cp, syneresis 28.49%, dry mater 25.24% and overall acceptability score was rated 4.75 counts out of 7.