The production of vinegar cider from spent coffee grounds

Abstract

This study suggests the vinegar production method, which utilizes spent coffee grounds (SCGs) as feedstock. The SCGs were pretreated by biotic degradation to obtain sufficient amounts of glucose. To do so, spore suspension (10⁷ spores/mL) from Aspergillus oryzae and Rhizopus oligosporus were prepared and 10% (v/v) of each suspension was separately introduced to the sterilized SCG mixture (1 g of SCG:100 mL of water). It was found that A. oryzae could produce higher amounts of glucose (54.68 g/L ± 0.08) than R. oligosporus (27.28 g/L ± 0.27). Saccharomyces cerevisiae TISTR 5020 was then inoculated to a liquid medium containing glucose derived from the pre-treatment step under anaerobic condition at 30^o C. The alcoholic fermentation was performed and gave a yield of 2.6% ethanol (v/v). After that, the vinegar was produced by the enzymatic reaction from Acetobacter aceti TISTR 102 at 30°C.
The highest amount of acetic acid reached 1.9% within 6 days. The vinegar from the SCGs was analyzed for antioxidant activity via DPPH and ABTS methods in comparison to 4 different kinds of vinegar in the markets including white wine, red wine, apple cider and jasmine rice vinegar. The SCG vinegar was shown to have higher antioxidant activity than some types of vinegar. This is the first study that utilized SCGs as feedstock for vinegar production. With this method, SCGs were not only valorized to vinegar, but also became a novel product for health-concern persons.