Nutritional biotransformation in traditional fermented tea (Miang) from north Thailand and its impact on antioxidant and antimicrobial activities.

Miang is a traditional fermented tea made from fermentation of Assam tea leaves with mixed microbial culture involving lactic acid bacteria and yeast. Miang has important bioactive benefits such as antioxidant and antimicrobial activity with relevance to health benefits. Miang is categorized into two processes; filamentous fungi growth-based (FFP) and non-filamentous fungi-based (NFP) process, depending on area of production. Further, Miang is also divided into 2 types; astringent Miang and sour Miang, depending on fermentation time. The aim of this research was to determine the important macronutrient biotransformation of Miang diversity under above processes and types and explore the impact on bioactive compounds relevant to antioxidant and antimicrobial activities. During fermentation, pH, total acid, nutritional components, total polyphenols (TP), total tannins (TT), total flavonoids (TF), total catechins (TC), antioxidant activity and antimicrobial activity were evaluated. Miang when fermented for longer sour Miang process compared to shorter time astringent Miang increased crude protein, fiber, and ash contents whereas soluble carbohydrates decreased. Even though TP, TT, TF and TC of sour Miang was lower, the overall antioxidant activity was higher than astringent Miang. This suggests that in addition to the phenolic compounds, other specific phenolics and substances such as biotransformed protein and fat could contribute to antioxidant properties. Additionally, Miang also contains antimicrobial activities against dental caries pathogenic bacteria Streptococcus mutans, gastrointestinal disease causing Vibrio cholerae and Salmonella enterica serovar Typhimurium through likely effects of organic acids and phenolic compounds.