Effect of Yeast Fermentation of Green Coffee Beans on Antioxidant Activity and Consumer Acceptability

Abstract

This study assessed the functionality and consumer acceptance of yeast fermented coffee beans. Green coffee beans were fermented for 24 h with three different yeast strains to increase functionality. The yeast fermentation was effective in fortifying the functionality of coffee by significantly increasing antioxidant activity according to the results of ORAC and SOD-like assay ( < 0.05). The TPC and TFC contents in the fermented coffee beans were significantly higher than those in the controls ( < 0.05). The consumer acceptance for the fermented coffee beans was slightly lower than that of the controls. Fermentation seemed to influence the aroma and flavor of coffee. However, agglomerative hierarchical clustering analysis revealed that approximately 39% of consumers significantly liked one of the fermented coffees (F3) more than the controls ( < 0.05). These consumers indicated that the yeast fermentation of green coffee beans did not generate a negative aroma or flavor and can be attractive with high antioxidant activity.

Antioxidant Activity, Total Polyphenol, Flavonoid and Tannin Contents of Fermented Green Coffee Beans with Selected Yeasts

“…The mean of the ORAC for the control (30.37 µMTE/mL) was significantly (p < 0.05) lower than that for the fermented coffee extracts. This result is in agreement with Kwak et al [19], who reported that green coffee beans fermented with yeasts showed a significant increment of ORAC values compared to non-fermented coffee beans. They also reported that there was no significant difference among the fermented coffee beans with respect to ORAC value, which supports our results.…”

“…This may be because of the action of the polyphenol oxidase enzyme which performs the diffusion of phenolics in cell liquids and oxidizes them. The results in our experiment are in agreement with reports on fermented seeds, where fermentation caused an increase in the phenolic content of seeds such as legumes [14][15][16][17][18], okra seeds [13], soybeans [12] and coffee [19]. In their natural form, phenolic compounds are combined or bound with sugar, which reduces their availability to the organism.…”

“…The fermented coffee extracts showed significant increases of SOD-like activity compared to the unfermented coffee ( Figure 6). Kwak et al [19] reported that yeast-fermented coffee extracts exhibited significantly higher SOD-like activity compared to unfermented coffee. Similarly, after fermentation of rice bran using baker's yeast and whiskey yeast, the SOD-like activities of the rice bran extract increased significantly compared to non-fermented rice bran extract [30].…”

“…Fermentation has improved the antioxidant activity and phenolic and flavonoid contents in fermented soybeans [12], okra seeds [13], legumes [14][15][16][17][18] and coffee [19]. As reported, soaking coffee beans in mulberry extract increases the antioxidant activity, total polyphenol content (TPC) and consumer acceptability [20].…”

“…However, the fermentation of green coffee beans to increase antioxidant activity and phenolic compounds has not been widely studied as a second processing step with respect to whether the coffee beans were obtained through dry-processing or wet-processing methods on the farm. To the best of the authors' knowledge, only one study has been published, by Kwak et al [19], regarding the fermentation effect on the antioxidant activity of green coffee beans fermented for 24 h and few studies have been published on the effect of fermenting green coffee beans on the aroma profile of the coffee. In previous experiments, green coffee was fermented with different yeast strains, yielding different unique results.…”