Effect of Proteın Polyphenol Interaction on The Physicochemical Properties of Set Type Yogurt and on the Digestibility of Milk Proteins

Abstract

The subject of protein-polyphenol interaction is of great interest to food science because of causing the physicochemical changes in protein structure, which results possibly in not only enhance the food product quality but also effect human health in the presence of polyphenols. The main focus of this thesis was to reveal the probable consequences of milk protein-polyphenol interactions in both the food and simulated human gastrointestinal system. In the first part, the effect of added different concentrations of green coffee powder and green tea powder, as polyphenol sources, on syneresis behavior which is described as a defect due to release serum phase from the gel matrix, and consistency of set yogurts were investigated. The results showed that the interaction between milk proteins and polyphenols improved the acid-induced gel network of set yogurts as confirmed by decreased syneresis rate and increased consistency during storage. But, green tea powder and green coffee powder behaved differently as a concentration-dependent manner in acidified gel networks of set yogurt, modifying its rheological behavior, as they have different profiles and concentrations of polyphenols. In the second part, the effect of the interaction of the milk proteins beta-lactoglobulin and micellar caseins (as micellar casein isolate) with either the polyphenol epigallocatechin-3-gallate or alternatively with a polyphenol-rich green tea extract on the modulation of protein digestibility promoted by gastrointestinal enzymes and free radical scavenging capacity of phenolic compound was studied. The results showed that the polyphenol binding is likely to alter protein structure leading to increased protein stabilization through gastrointestinal tract. In addition, the free radical scavenging capacity for polyphenols gradually decreased resulted in interaction with protein, especially casein, from beginning to the end of the digestion.