Abstract: This study aimed to evaluate changes in the quality and antioxidant activity during the fermentation of papaya juice by lactic acid bacteria (a mixture of Lactobacillus bulgaricus and Streptococcus thermophilus). The results showed that the strains exhibited good viability and high acid-producing ability after 48 h fermentation, as demonstrated by a pH decrease from 5.36 to 3.11 and a simultaneous decrease in reducing sugar content from 8.69% to 5.15%. The antioxidant activity was evaluated by four different assays. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity of papaya juice decreased to a level higher than 50% after 48 h fermentation. Large amounts of organic acids were produced during the fermentation process, including 1 264.39 mg/100 mL of lactic acid. Esters were the most abundant volatile compounds in the fermented juice. The number of ketones was highest among the new compounds formed during fermentation. Thus, papaya juice fermented with lactic acid bacteria could be used as a novel functional beverage.

Key words: papaya, lactic acid bacteria, antioxidant activity, organic acids, aroma components