Key Odorants and the Role of Microorganisms on Aroma Formation of Post-Fermented Tea, Goishi Tea

Abstract

　Goishi tea, a post fermented tea, is produced in Otoyo town, Kochi Prefecture, Japan. The aim of the present study was to elucidate the aroma-active components in Goishi tea by aroma extract dilution analysis (AEDA) using gas chromatography-olfactometry (GC-O) and identify the microorganisms involved in the fermentation process to further understand the aroma formation. Based on AEDA in GC-O, profiles of various aromatic compounds in Goishi tea were analyzed. Hexanoic acid had the highest flavor dilution (FD) value, followed by furfural, furaneol, and ethyl furaneol. Three microorganisms, namely, Aspergillus niger, Pichia manshurica, and Lactobacillus plantarum were isolated and identified based on their rDNA sequences. We prepared post fermented tea using these microorganisms, and the aromatic extract from each tea was investigated to assess the relationship between aroma formation and the microorganism. Ethyl furaneol and thiazoline compounds produced by A. niger were detected in post fermented tea. Ester, alcohol, and phenolic compounds including 4-ethylphenol and 4-ethyl-2-methoxyphenol were detected in the tea with P. manshurica. L. plantarum produced organic acids such as hexanoic and butanoic acids and lactone. Thus, all the three strains, A. niger, P. manshurica, and L. plantarum contributed considerably to aroma formation in Goishi tea.