Optimization of polyphenolic fortification of grape peel extract in stirred yogurt by response surface methodology

Abstract

Black grape ( Vitis vinifera ) peel possesses a huge amount of nutraceuticals. In the present study, dried grape peel extract (GPE), milk fat and powdered sugar levels in stirred yogurt were optimized with the help of response surface methodology involving central composite rotatable design of three independent variables. Four important parameters, total phenolic content, antiradical activity, textural properties and sensory characteristics were chosen for the optimization process. It was found that the antiradical activity and total phenolic content increased exponentially with increase in GPE levels. Textural and sensory attributes like consistency, cohesiveness, flavor and overall acceptability of yogurt was found directly proportional to the milk fat. On the other hand, the pH and titrable acidity were found to be inversely proportional to the concentration of GPE in yogurt. On the basis of interactive studies, grape peel extract, milk fat and sugar were optimized in 1.00, 4.00 and 10.00%, respectively.