Effect of dilute sulfuric acid pretreatment on the physicochemical properties and enzymatic hydrolysis of coffee cut-stems

Coffee-cut stems are a potential fermentable sugars source, which can be upgraded in different value-added products and energy vectors. Nevertheless, there are few reports focused on the acid pretreatment and saccharification processes. Thus, this paper evaluates the effect of the acid pretreatment and saccharification conditions of coffee cut-stems to find the highest sugar yield. Thereafter, the influence of the residence time in the acid pretreatment and the -glucosidase supplementation in the saccharification process were analyzed. The combined severity factor and crystallinity index were used as metrics to evaluate both processes. In all assays, an increase in the crystallinity index was observed. Furthermore, a nonlinear trend of the combined severity factor respect to the residence time in the acid pretreatment was evidenced. The highest sugar yield was 66.75% with a combined severity factor of 1.84. The better saccharification process was achieved at combined severity factor of 2.01 with a digestibility of 43%. The addition of -glucosidase in the enzymatic hydrolysis allows increasing the value to 69.07%. Hence, low temperatures, acid concentrations, and the -glucosidase supplementation allows obtaining a high sugar yield from coffee cut stems.The authors express their gratitude for the financial support to the Programme of ERASMUS + - International Credit Mobility celebrated between the Universidad Nacional de Colombia at Manizales and the University of Minho. The COLCIENCIAS program “Jóvenes Investigadores e Innovadores, Convocatoria 761 de 2016”, the international collaboration project COLCIENCIAS – CONICYT with code PCCI140052, HERMES code 23567 (23876) entitled “Análisis Tecno-económico y Ambiental de Biorefinerías a partir de Residuos Lignocelulósicos con Esquemas de Recirculación de Microorganismos”, the research program entitled “Reconstrucción del tejido social en zonas posconflicto en Colombia” SIGP code: 57579 with the project entitled “Competencias empresariales y de innovación para el desarrollo económico y la inclusión productiva de las regiones afectadas por el conflicto colombiano” SIGP code 58907. Contract number: FP44842-213-2018.info:eu-repo/semantics/publishedVersio