Valorization and Functional Enhancement of Mature Assam Tea Leaves Through Indigenous Filamentous Fungi-Based Fermentation for Functional Drink Development

Miang, a traditional fermented tea produced from Camellia sinensis var. assamica, is of notable cultural and socio-economic relevance in Northern Thailand. Traditionally, the non-filamentous fungi-based process (NFP) in western Lanna uses only young tea leaves, resulting in substantial amounts of mature leaves being discarded as agricultural waste. This study aimed to utilize the mature tea leaves by adapting the filamentous fungi growth-based process (FFP) of eastern Lanna using selected tannin-tolerant microorganisms, including Aspergillus niger MLF3, Cyberlindera rhodanensis P3, and Lactiplantibacillus pentosus A14-6. Study on fermentation dynamics and bioactive compound formation based on a 2-step fermentation process: 3-day solid-state fermentation with A. niger MLF3, followed by 7-day submerged fermentation by co-culture of C. rhodaninsis P3, and L. pentosus A14-6 in 500 mL sterile distilled water at 30 °C. Increased activities of polysaccharide-degrading enzymes and organic acids were clearly observed during solid-state fermentation, while the significant changes in polyphenol, antioxidant, and reducing sugar content in cell-free supernatant (CFS) were found after submerged fermentation. The obtained CFS shows inhibitory effects of 90 ± 2.5% and 95 ± 1.8% on α-glucosidase and α-amylase, respectively. Analysis of CFS by E-tongue and E-nose clearly indicated the influence of microbial mixture on the taste and aroma of the fermented products. These results demonstrate not only a high-yielding strategy for the effective biotransformation of mature tea leaves into functional drink products but also significant implications for reducing agricultural waste.