Comparison of Probiotic Fermentation in Pasteurized and Filter Sterilized Red Dragon Fruit Juice

Wong, Chia Yen (2016) Comparison of Probiotic Fermentation in Pasteurized and Filter Sterilized Red Dragon Fruit Juice. Final Year Project (Bachelor), Tunku Abdul Rahman University College.

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Abstract

Red dragon fruit juice (RDFJ) contains plenty of nutrients such as sugar, amino acids, fatty acids, antioxidants, vitamins and minerals, and prebiotics. Thus, it is a potential medium for cultivating probiotics which exert a number of health-promoting effects. This project attempted to determine the best sterilization method between pasteurization and filter sterilization for the fermentation of Lactobacillus casei in RDFJ and the fermentation time to produce the highest concentration of probiotic. Fresh juice samples were subjected to pasteurization at 75°C for 15 sec and filter sterilization using membrane filter of 0.45 μm followed by syringe filter with pore size of 0.2 μm. The juice samples were then inoculated with Lactobacillus casei and incubated under microaerophillic condition at 37°C for 0 to 3 days. Unfermented juice samples were used as control. Samples were taken every day for determining viable cell count by standard plate count and also for determination of total soluble solid (ºBrix), pH and total titratable acidity (TTA). The statistical analysis was performed using the program SPSS 20, performing independent sample t-test and ANOVA with subsequent Tukey test for comparison of means with a confidence interval of 95%. The result showed that the probiotic population was the highest at day 2, with more than 2 log CFU/mL increment for both treatments. The two treatments were significantly different from each other (p < 0.05), with higher cell increment, lower Brix and pH and higher TTA observed for pasteurized RDFJ. In conclusion, the overall results suggested that pasteurization may serve as a better sterilization method, which produced the highest bacterial population after fermented for 2 days. It was recommended to test on other sterilization method and include sensory evaluation in future research.