Carbohydrate conversion in spent coffee grounds: pretreatment strategies and novel enzymatic cocktail to produce value-added saccharides and prebiotic mannooligosaccharides

Background

Spent coffee grounds (SCG) are the most abundant waste byproducts generated from coffee beverage production worldwide. Typically, these grounds are seen as waste and end up in landfills. However, SCG contain valuable compounds that can be valorized and used in different applications. Notably, they are rich in carbohydrates, primarily galactomannan, arabinogalactan type II, and cellulose. Within the framework of a circular bioeconomy, the targeted degradation of these polysaccharides via a tailored cocktail of carbohydrate-active enzymes offers a promising strategy for producing high-value saccharides from coffee waste.

Results

In this study, various mild pretreatments were evaluated to increase the enzyme accessibility of SCG-derived biomass, reduce lignin content, and minimize hemicellulose loss. Thermostable enzymes were selected to construct an enzymatic cocktail specifically targeting cellulose and hemicelluloses in pretreated SCGs. The approach used achieved a conversion of 52% of the polysaccharide content to oligo- and monosaccharides, producing 17.4 mg of reducing sugars and 5.1 mg of monosaccharides from 50 mg of SCG. Additionally, microwave pretreatment followed by the application of a thermostable endo β-mannanase resulted in the production of 62.3 mg of mannooligosaccharides from 500 mg of SCG. In vitro experiments demonstrated that the produced mannooligosaccharides exhibited prebiotic activity, promoting the growth and biofilm formation of five probiotic bacterial strains.

Conclusions

This study highlights an effective strategy for the valorization of SCG polysaccharides through mild pretreatment and customized enzymatic cocktails in a circular bioeconomic context. The production of both monosaccharides and oligosaccharides with prebiotic activity illustrates the versatility and commercial potential of SCG as a substrate for high-value saccharides. Furthermore, the use of mild pretreatment methods and thermostable enzymes minimizes chemical inputs and energy demands, aligning with sustainable processing practices. The ability to selectively target and degrade specific polysaccharides within SCG not only enhances the yield of desirable products, but also preserves key structural components, reducing waste and promoting resource efficiency.