Background and objective: Fermented noni (Morinda citrifolia L.) fruit juice is considered as one of the health-promoting beverage. The food industries are working on further improvement of fermented noni juice. The objective of the current study was to assess the impact of green tea (GT) extract during the lactic acid bacteria (Lactobacillus plantarum SK15) mediated fermentation of noni fruit juice.
Materials and methods: The clean-diced noni fruits were blended with sugar, water, 10% SK15 and GT extract. The mixture was kept at 30°C for 25 days. During fermentation, samples were collected. The changes in pH, acidity, alcohol, sugar, pectin content, total phenolic content (TPC), antioxidant capacity (AC), pectin methylesterase (PME) activity and microbial load were assessed.
Results: The fermented noni fruit juice exhibited significantly low pH, sugar and pectin content. TPC and AC were increased after fermentation. The alcohol content, especially methanol volume was increased in all the samples but not exceed the lethal level. The samples with GT extract exhibited superior quality in all measured aspects. Notably, PME activity was suppressed by GT extract, which was reflected in the methanol content of the respective samples when compared to control.
Conclusion: The results suggested that GT extract could be used in the production of fermented plant beverages to prevent the indigenous PME activity (to reduce the methanol formation) and to improve the AC of the product. Further studies are required to know the fate of other phytochemicals and volatile compounds in noni fruit juice during fermentation.
Keywords: Morinda citrifolia L.; antioxidant capacity; green tea; lactic acid bacteria; noni; pectin methylesterase; phenolic content.