Abstract: Changes in the composition and bioactivities of a mixture of Chinese yam pulp, apple juice and tomato juice during fermentation by lactic acid bacteria were assessed through the determination of its physicochemical and microbial properties, enzyme activities, and antioxidant and antibacterial activities. Results showed that pH and total acid content changed fast from the second day to the fourth day of fermentation, and then remained stable after 8 days. Total sugar content declined firstly, then increased, and finally declined again, reaching and maintaining a minimum level after 12 days. Nitrite content reached the highest value on the fourth day but reduced to a minimum level 10 days later. The microbial growth mainly occurred during the first 6 days, and lactic acid bacteria gradually became the dominant bacteria during the fermentation, inhibiting the growth of other bacteria. The activities of superoxide dismutase, amylase, protease and lipase were increased gradually with fermentation time. Superoxide dismutase activity was highest whereas lipase activity was lowest. DPPH radical scavenging, hydroxyl radical scavenging, superoxide anion radical scavenging and total antioxidant activity were increased gradually during fermentation until reaching a plateau after 10 days. The inhibition percentages against Escherichia coli and Staphylococcus aureus were increased gradually during fermentation, reaching the highest value after 12 days of fermentation. This study may provide a theoretical basis for the development of functional products based on lactic acid fermentation of fruit and vegetable blends.

Key words: yam, lactic acid bacteria, fermentation, composition, bioactivity