Procuring biologically active galactomannans from spent coffee ground (SCG) by autohydrolysis and enzymatic hydrolysis.

Spent coffee grounds (SCG) are a promising raw material for galactomannan (GalM) production based upon its enrichment in galactomannan polysaccharides. In this work, SCG was pretreated by autohydrolysis for maximumly improving GalM extractability by endo-mannanase. The GalM in the prehydolyzate (GalM-PH) and enzymatic hydrolyzate (GalM-EH) were obtained by ethanol precipitation and characterized. Under the optimized autohydrolysis conditions, 50.1% of GalM in pretreated SCG was converted into free GalM in enzymatic hydrolyzate. Compositional analysis results revealed that GalM-PH was comprised of 81.7% galactomannan, higher than that of GalM-EH (76.4%). The molecular weight of GalM-PH and GalM-EH were 44.5 kDa and 28.0 kDa, respectively. Antioxidant assays indicated that both GalM-EH and GalM-PH could scavenge 2,2-diphenyl-1-picryl-hydrazyl radicals and hydroxyl radicals. Immunological and prebiotics analysis showed all GalM preparations exhibited pronounced activities for proliferating the probiotics and proliferating the Macrophages cell for NO production, in which the GalM-EH outperformed the GalM-PH. These results imply that the GalM extracted from SCG are the bioactive substances that can be used as antioxidant, prebiotics, and immunostimulants.