Effect of fermentation conditions on microorganisms during fermentation of Ishizuchi-kurocha

Abstract

In this study, we examined the effects on microorganisms of Ishizuchi-kurocha depending on the production container, the position during fermentation, and the production lot. Ishizuchi-kurocha is produced in Ehime Prefecture, Japan, and produced by tea leaves through two-step fermentation: aerobic fermentation followed by anaerobic fermentation. In the traditional production method, wooden barrels were used for the anaerobic second fermentation, but now plastic buckets are used. Microorganisms were isolated from the inner and outer layers of tea leaves at each fermentation stage, and the microbial community structure was analyzed using a nextgeneration sequencer for tea produced in multiple lots in the same year using plastic buckets or wooden barrels during the second fermentation. Regardless of the production conditions, molds of the genus Aspergillus were dominant in the primary fermentation and lactic acid bacteria were dominant in the secondary fermentation, suggesting normal fermentation progression. On the other hand, there were differences in yeast species depending on the production container used for secondary fermentation. Although differences in manufacturing containers do not affect the dominant species, they are thought to affect the growth and type of yeast, which may affect the flavor of Ishizuchi-kurocha. In addition, the influence of the position during fermentation was also confirmed, as lactic acid bacteria were detected inside the tea leaves after primary fermentation. The findings obtained from this study are thought to lead to the application of the traditional manufacturing method and stabilization of Ishizuchi-kurocha production.