Biotransformation of spent coffee grounds by fermentation with monocultures of Saccharomyces cerevisiae and Lachancea thermotolerans aided by yeast extracts

Spent coffee grounds (SCG) is a low-value solid food waste generated from the rising consumption of coffee. There is a need to transform the huge amount of SCG to value-added products such as alcoholic beverages. In this study, monocultures of Saccharomyces cerevisiae Merit and Lachancea thermotolerans Concerto were used to ferment SCG hydrolysates supplemented with yeast extracts. The addition of yeast extracts slightly enhanced the growth of both S. cerevisiae Merit and L. thermotolerans Concerto. In addition, the yeast extracts also increased the production of organic acids (e.g. succinic acid and acetic acid) and volatiles such as 2-phenylethyl alcohol and ethyl esters (e.g. ethyl octanoate and ethyl 2,4-hexadienoate). Furthermore, the supplementation of yeast extracts showed a more significant effect on the performance (e.g. yeast growth) of S. cerevisiae Merit than that on L. thermotolerans Concerto. Our results indicated that the addition of yeast extracts may provide a new strategy to enhance the transformation of SCG into a potential alcoholic beverage with flavor compound complexity.