Functional Of Yogurt On The Physicochemical Properties, Antioxidant Activity, And Microstructure Were Studied

Combined probiotics of Streptococcus thermophiles and Lactobacillus delbrueckii subsp. bulgaricus were used as fermentation starter culture in this paper. By adding different concentrations of bilberry extract (BE), tea polysaccharides (TPA) and tea polyphenol (TPP), durian extract (DE) in yogurt that physicochemical properties, rheological characteristics, antioxidant activity and microstructure studied in this paper.Effects of different concentrations of bilberry extract, tea polysaccharides and tea polyphenol, durian extract on the pH, acidity, WHC, firmness of yogurt were studied. Results indicated that the pH and acidity of BE and TPA did not change significantly. The pH of 0.4% TPP of yogurt increased significantly (P<0.05) compared with that of the control sample. With increasing DE concentration, pH of yogurt decreased significantly (P<0.05), acidity increased significantly (P<0.05). With increasing concentration of BE, the WHC increased at first but then decreased. Adding 0.25% and 0.4% TPA into yogurt can increase significantly its WHC (P<0.05) compared with that of the control sample,0.4% TPP of yogurt increased significantly (P<0.05). With increasing DE concentration, yogurt WHC increased significantly (P<0.05). With increasing concentration, BE, DE and TPA of yogurt firmness decreased significantly (P<0.05).0.25% and 0.4% TPP firmness decreased significantly (P<0.05).Effects of different concentrations of bilberry extract, tea polysaccharides and tea polyphenol, durian extract on the apparent viscosity (ηapp), storage modulus (G’), and loss modulus (G") of yogurt were studied. The apparent viscosity was calculated at γ =1 s-1. With increasing its concentration, the ηapp of BE-yogurt increased at first and then decreased, the ηapp of TPA-yogurt and TPP-yogurt increased significantly (P<0.05), the ηapp of DE-yogurt decreased significantly (P<0.05). At deformation frequency, with increasing frequency, storage modulus of BE-yogurt, TPA-yogurt, TPP-yogurt, and DE-yogurt increased significantly. The tanδ BE-yogurt, TPA-yogurt, TPP-yogurt, and DE-yogurt were slightly curved with a local minimum at 1-1.5 Hz, and tan 8 of TPA-yogurt decreased at ranges of 0.01-10 Hz. The storage modulus (G’) of all of yogurt samples, decreased linearly with increasing temperature until approximately 13℃; thereafter, the storage modulus (G’) decreased rapidly. However, loss modulus (G") decreased rapidly with increasing temperature until approximately 33℃.Effects of different concentrations of bilberry extract, tea polysaccharides and tea polyphenol, durian extract on the DPPH radical scavenging activity and microstructure of yogurt were studied.0.1% and 0.25% TPA and DE addition to yogurt, the DPPH radical scavenging did not significantly. With increasing concentration, DPPH radical scavenging of BE-yogurt and TPP-yogurt increased significantly (P<0.05). In microstructure studies, the protein network was more compact and contained less void space within the network in yogurt samples with BE, TPA, and TPP than in the control sample.