Pomegranate juice powder improving quality attributes of yogurts by replacing sucrose in fermentation matrix

Abstract: Pomegranate is rich in polyphenols and is an excellent source of antioxidants, such as polyphenolic substance. However, the concentration of the harvest time, poor shape and inconvenient for eating have limited the sale of pomegranates. Therefore, the processing of pomegranate is beneficial to the appreciation of pomegranate resources. Yogurt a good carrier for bioactive compounds that may offer additional health benefits, is a fermented dairy product suitable for all ages, and the new type yogurts with high qualities and extra functions are more favored by consumers. In order to accelerate the development of pomegranate processing industry, enrich the variety of yogurts and improve the quality of yogurts, in this paper, 1%, 3% and 5% pomegranate juice powder (PJP) whose contents of total carbohydrate, soluble protein and total polyphenols were 0.88 g/g, less than 1.0 mg/g and 0.471 0 mg/g, respectively, was used to replace sucrose in the matrix of set yogurt and the effects of PJP replacement on the parameters in fermentation process, including pH value, titratable acidity, apparent viscosity and lactic acid bacteria vitality were analyze. The Raman spectra, textural properties, rheological properties, total phenolic content and antioxidant activity of the set yogurt with and without PJP replacement were compared. The results indicated that PJP instead of sucrose does not significantly change the pH value, titrable acidity, apparent viscosity and Raman spectrum of the yogurt matrix at the end of fermentation, but the substitution of PJP had a significant (P< 0.05) effect on lactic acid bacteria during fermentation and the properties of yogurt. The replacement of sucrose by PJP defered the solidification time of yogurt, the exponential growth time and the maximum activity time of lactic acid bacteria, but it significantly (P<0.05) increased the maximum activity of lactic acid bacteria in yogurt. It took the control, LD, MD and HD groups 300 minutes, 240 minutes, 260 minutes and 280 minutes, respectively, to reach (4.6±0.1) of pH value, suggesting PJP replacement shortened the fermentation time. The lactic acid bacteria activity of the pomegranate yogurt was 6-7 times that of the control yogurt at the completion of fermentation. What's more, the substitution of PJP could significantly improve the quality of yogurt. The firmness, consistency, cohesiveness and index of viscosity of the control were (65.6±1.9) g, (939.8±61.8) g·s, (14.5±0.8) g and (36.5±9.2) g·s, respectively; while the HD group showed 1.84, 2.26 and 1.76 times that of the control, respectively. PJP-replacement yogurt showed better texture, viscoelasticity and antioxidant activity. Compared with the control, when sucrose was completely replaced by PJP, the total polyphenol content, FRAP and DPPH clearance rate were 1.84 times, 2.26 times and 1.76 times, respectively. Sensory test results showed that PJP substitution of sucrose had a positive effect on the appearance, texture and taste of yogurt, which may be related to the phenolic substance in PJP and the casein interaction in yogurt. PJP can significantly improve the health benefits and quality of yogurt, which is expected to replace sucrose to make healthier yogurt.