Optimization of alkali-catalyzed organosolv treatment of spent coffee grounds for obtaining polysaccharides

The coffee industry is growing rapidly and generating increasing amounts of spent coffee grounds annually. Spent coffee grounds contain high levels of polysaccharide, which needs in-depth research to obtain and transform into value-added products. This study was carried out to optimize the alkali-catalyzed organosolv treatment of spent coffee grounds to enrich the polysaccharide content. A three-factor central composite design of the response surface model was used to optimize the treatment variables including reflux time, NaOH, and acetone concentration to yield the highest polysaccharide level. As a result, the maximum polysaccharide content was 73.13% obtained at a reflux time of 4.5 h, 62% acetone with 0.91% NaOH. The polysaccharide-rich material from spent coffee ground was composed of 39.37% mannan, 10.40% glucan, and 9.33% galactan. Partial removal of lignin and protein was observed during the treatment. Enzymatic hydrolysis of the spent coffee polysaccharides released the highest reducing sugars of 5583 mg/L using an enzyme cocktail containing 4% of cellulase and 1% of mannanase after 96 h. The enzymatic hydrolysate contained 3190 mg/L mannose and 1790 mg/L glucose, showing a feasible transformation of spent coffee polysaccharides.