Spent coffee ground mass solubilisation by steam explosion and enzymatic hydrolysis

Abstract

AbstractBACKGROUNDInstant coffee production generates large amounts of a waste known as spent coffee ground (SCG), which is rich in carbohydrate (∼50%), oil and aromatic compounds.RESULTSSteam pretreatment by itself solubilised up to 10.7% of the SCG mass, which was recovered as soluble solids in the liquor from pretreatment. The highest extent of soluble solid recovery from pretreatment itself (10.7%) was obtained at 210°C/15 min, while milder conditions (150–190°C/10–12 min) recovered 2.6% soluble solids. Mannanase (recombinant strain of Yarrowia lipolytica) and cellulase (Acremonium, Bioshigen Co.Ltd, Japan) had an additive effect, with no indication of synergism observed. The best combinations of mannanase/cellulase cocktail for enzymatic hydrolysis were 0.5/0.82% and 0.01/0.91% (w/w), releasing 20.6% (g per 100 g raw SCG) and 22.6% (g per 100 g pretreated SCG) of soluble solids from untreated and pretreated SCG, respectively. By combining soluble solids recovered from steam pretreatment with the soluble products from subsequent enzymatic hydrolysis, a yield of 27.65% (g per 100 g SCG) was achieved.CONCLUSIONThe pretreatment was effective in generating a material more amenable to enzyme action, thus requiring reduced enzyme dosages for subsequent hydrolysis compared with untreated SCG. The combined process showed significant technical feasibility for re‐use SCG and may be considered to produce additional instant coffee product. © 2014 Society of Chemical Industry