Abstract:Freshly squeezed and sterilized blueberry and blackberry juice mixture was used as the raw material for the fermentation with three different lactic acid bacteria (Lactobacillus plantarum, Lactobacillus lactis and Leuconostoc mesenteroides). The changes in the number of live lactic acid bacterium colonies, pH value, total acid, total sugar, reducing sugar and total phenolic content, in vitro antioxidant activity and bacteriostatic effect during fermentation were studied. The results showed that the lactic acid bacteria grew well in the juice mixture, with the highest colony number of viable bacteria (1.23×108 cfu/mL) occurring at the 24th h. During the fermentation, the pH value decreased constantly (from initial 5.50 to 3.75) while the total acid content increased continuously (from 0.15 to 2.15 g/100 mL). The reducing sugar content increased briefly and then decreased with the peak value (2.63 g/L) at 6 h, while the concentration of total sugar decreased steadily, due to the consumption by microorganisms, till almost 0 g/L after 42 h of fermentation. The content of phenolic compounds changed from 2.32 to 3.26 mg/mL (increase by 40.52% after fermentation). The DPPH·, hydroxyl and superoxide anion free radical scavenging rates increased by 18.17%, 30.67% and 34.55%, respectively, after fermentation. The fermented juice mixture significantly inhibited Escherichia coli, Aspergillus niger, Saccharomyces cerevisiae and Staphylococcus aureus, and the inhibitory activities increased gradually with fermentation time. Therefore, the use of fermentation by composite lactic acid bacteria is of high significance in terms of improving the quality of the blueberry and blackberry juice mixture and developing functional food products.
