Evaluation of the effects of fermentation on the non-volatile compounds in semi-dry coffee beans using widely targeted metabolomics analysis.

This study was the first to investigate the differences in non-volatile metabolites and their relationships with the sensory attributes of Hainan Robusta coffee by yeast fermentation [four single strains (HK, JK, GK and ZK), one mixed strain (MK), and natural fermentation (CK)] via widely targeted metabolomics. The results indicated that GK led to a change in the brew coffee color and obtained the highest scores for mouthfeel (7.67), aftertaste (7.50) and balance (7.75). A total of 127 key differential non-volatile metabolites were identified, including organic acids, phenolic acids, flavonoids and alkaloids etc. An increase in luteolin (5,7,3',4'-tetrahydroxyflavone) was noted in all fermented coffee and the increase was the most significant in HK (1147-fold), although it was the only strain that caused a decrease in lignans and coumarins. Pentahydroxyflavone, protocatechualdehyde, 5-phenylvaleric acid, and naringenin (5,7,4'-Trihydroxyflavanone)*, contributed the most to balancing sensory attributes.