A study on the production of fermented watermelon juice using probiotic cultures

In this study, the production of fermented watermelon juice from fresh-squeezed watermelon juice using lactic acid bacteria of Lactobacillus helveticus NRRL B-4526 standart strain, Lactobacillus acidophilus KPb4b and Lactobacillus plantarum was aimed. Fresh-squeezed watermelon juice inoculated by lactic acid bacteria were left for lactic acid fermentation during 18 hours at 37 °C. Total aciditiy, pH, total viable lactic acid bacteria, colour and soluble solid content were analysed during fermentation. In addition, chemical (sugar, total antioxidant activity and total phenolic compunds) and sensory analyses were performed on samples at the begining and end of the fermentation.According to results of research, pH decreased with a concomitant increase of the total acidity during fermentation. The counts of total viable lactic acid bacteria rised significantly in all samples. Maximum number of with 10.0 log kob/mL was found in the sample inoculated by Lb. plantarum. In fermented watermelon juices, total aciditiy (as lactic acid) and pH contents varied in the range of 1.16-3.30 g/L and 4.28-4.81.Lactic acid fermentation affected colur parameters of watermelon juices beneficially. CIE-L*, a* ve b* parameters of all samples after fermentation were found higher than before fermantation.Soluble solid and total sugar content of samples decreased during fermentation. As saccharose and glucose content of samples were increasing, fructose content reduced.Total phenolic compounds of fermented watermelon juices were more than total phenolic compounds of unfermented watermelon juice. While total phenolic compunds content of samples were varied in the range of 133.86-137.04 mg catechin equivalent/L at the beginning of fermentation, this range were changed as 151.86-201.94 mg catechin equivalent/L at the end of fermentation. It was determined that watermelon juice by inoculated Lb. plantarum had maximum number of total phenolic compounds with number of 201.94 mg catechin equivalent/L.Total antioxidant activity was analysed by TEAC (Trolox Equivalent Antioxidant Capacity) method. Total antioxidant activity of all samples increased during fermentation. While total antioxidant activity of samples was found in the range of 3.78-4.88 µM TE/100 g at the beginning of fermentation, this range were 4.60-7.53 µM TE/100 g at the end of fermentation. It was determined that watermelon juice inoculated by Lb. plantarum had the highest antioxidant activity with 7.53 µM TE/100 g.According to the results of sensory analyses, the most preferred watermelon juice were the sample produced by Lb. plantarum. The level of general preference of other three samples, exception of sample produced by Lactobacillus plantarum, decreased significantly after fermentation proccess.