Microwave superheated water extraction of polysaccharides from spent coffee grounds

► Microwave assisted extraction (MAE) allows the recovery of arabinogalactans (AG). ► Re-extraction of the material left (MAE2) allowed to recover galactomannans (GM). ► 74% and 66% of total galactose and mannose could be extracted from spent coffee grounds. ► Oligosaccharides, mainly derived from GM, can be obtained in MAE2. ► Different proportions of GM/AG can be obtained depending on operating conditions. The spent coffee grounds (SCG) are a food industry by-product that can be used as a rich source of polysaccharides. In the present work, the feasibility of microwave superheated water extraction of polysaccharides from SCG was studied. Different ratios of mass of SCG to water, from 1:30 to 1:5 (g:mL) were used for a total volume of 80mL. Although the amount of material extracted/batch (MAE1) increased with the increase of the concentration of the sample, the amount of polysaccharides achieved a maximum of 0.57g/batch for 1:10. Glycosidic-linkage composition showed that all extraction conditions allowed to obtain mainly arabinogalactans. When the unextracted insoluble material was re-extracted under the same conditions (MAE2), a further extraction of polysaccharides was observed (0.34g/batch for 1:10), mainly galactomannans. Also, a high amount of oligosaccharides, mainly derived from galactomannans, can be obtained in MAE2 (0.96g/batch for 1:10). This technology allows to obtain galactomannans and arabinogalactans in proportions that are dependent on the operating conditions.