Influence of orange fiber addition on quality of orange fruit yogurt using response surface method

Response surface methodology (RSM) was employed to investigate the combined effects of orange fiber (0, 0.2, 0.6, 1 and 1.2 g/100ml) and storage time (3, 7, 16, 25, 29 days) on physicochemical, rheological and sensory properties of orange fruit yogurt. Results showed that by increasing the fiber amount, the viscosity and total solids increased and syneresis decreased significantly (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 led to increasing the yellowish spectrum (+b* parameter) of yogurt while the rate of lightness (L*) decreased significantly (P<0.05). Sensory evaluation results showed that higher flavor, color and overall acceptance score was obtained at lower fiber amount. However, hedonic tests showed that almost all assayed yogurts have color, flavor and overall acceptance scores at least 4.25 on a seven-point scale, considered in the present work as the acceptable value. Analysis of variance revealed that the quadratic models are well adjusted to predict the experimental data. Finally, the optimum conditions for production of orange yogurt containing orange fiber were obtained using 1.2%fiber after storage for 16 days.