Impact of Storage on the Physicochemical Properties of Acidified Milk Gels Fortified with Polyphenols

Understanding the impact of storage on the properties of dairy products containing polyphenols is important. The objective of this study was to determine the impact of storage (28 days, 4°C) on the properties of acidified milk gels fortified with green tea, white grape, tannic acid, or gallic acid (1 mg ml-1). Polyphenols were added to pasteurised skim-milk which was heat treated (85oC, 30 min), acidification was achieved by addition of GDL (1.7% w/w, 30°C, 3.75 hours). Samples (n=80) were analysed for total phenolic content (TPC) and antioxidant capacity (AC), syneresis capacity, pH, textural properties, and colour, in 7 day intervals. The TPC, AC and syneresis capacity of the gels, except tea, did not change during storage (P>0.05). The hardness of the tea and grape samples significantly increased (P=0.01-0.05) during storage. However, no change in the hardness of control, tannic and gallic were observed. Phenolic addition and storage influenced the colour parameters. Overall the tea sample tended towards a red colour (+a*) with the others similar to the control (-a*). During storage the lightness and pH of all samples, except gallic lightness, decreased. In conclusion, polyphenols may be added to milk gels with minimal impact on physicochemical properties during storage.