Functional Food Potential of Green Tea Waste (Used Tea Leaves) Through Lactic acid Fermentation

Aims: Fermented functional foods were developed to utilize green tea waste (used tea leaves) and their antioxidative activity was examined. Methodology: The initial tea waste was prepared by steeping regular tea leaves in deionized water at 90°C for 60 s. This procedure was repeated to obtain the fifth and tenth sequential extracts. Subsequently, lyophilized tea leaves were rehydrated with potable water and inoculated with Lactococcus lactis subsp. cremoris. Following thorough mixing, the inoculated sample was fermented under anaerobic conditions at 25°C in the absence of light. To monitor the progress of fermentation, the pH levels of the infusion were measured on days 1, 3, 7, and 14. Additionally, the antioxidative activity of the fermented tea leaves and their infusions was assessed using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay. Results: After one week of lactic acid fermentation, the pH of the infusions from the fifth and tenth tea leaf extracts decreased significantly compared to other samples. However, within two weeks, all sample infusions reached a pH below 4, suggesting that catechins in the used tea leaves may inhibit lactic acid production during the early stages of fermentation. Despite the multiple extractions, the tea leaves from the fifth and tenth extracts retained elements that supported fermentation. Furthermore, the infusion prepared from the tea leaves after the tenth extract continued to exhibit antioxidative activity, indicating that beneficial properties persist even after repeated extractions. Conclusion: Tea waste can be effectively utilized for lactic acid fermentation. Moreover, the resulting infusion may provide health benefits, making it a potential functional food.