Optimal fermentation time for Nigrospora‐fermented tea rich in bostrycin

Abstract BACKGROUND Bostrycin has many biological functions, such as anticancer activity, and is becoming increasingly popular. Nigrospora sphaerica HCH285, which has the ability to produce high levels of bostrycin, can be used to ferment sun‐dried green tea of Camellia sinensis through acclimation, resulting in the development of a Nigrospora ‐fermented tea. The effects of fermentation time on the production of bostrycin by the HCH285 strain were investigated. RESULTS After 45 days of fermentation, the bostrycin content reached 3.18 g kg –1 , which is the highest level during the whole fermentation. At 50 days, the tea liquor was red, had a strong mushroom odour and a sweet taste, and presented optimal quality. The contents of free amino acids, tea polyphenols and soluble sugars in the fermented tea decreased generally during the fermentation, although the content of water‐soluble substances increased. Additionally, the results of a 14‐day acute oral toxicity test showed that Nigrospora ‐fermented tea was nontoxic. CONCLUSION The optimum fermentation time of Nigrospora ‐fermented tea was concluded to be 45–50 days. These results provide insights with respect to the development of tea biotechnology and new tea products with active ingredients. © 2020 Society of Chemical Industry