Efficient Recovery of Glucose and Fructose via Enzymatic Saccharification of Rice Straw with Soft Carbohydrates

Soft carbohydrates, defined as readily-recoverable carbohydrates via mere extraction from the biomass or brief enzymatic saccharification, were found in significant amounts in rice straw as forms of free glucose, free fructose, sucrose, starch, and β-1,3-1,4-glucan. In this study, we investigated their amounts in rice straw (defined as culm and leaf sheath), and developed an easy method for glucose and fructose recovery from them with heat-pretreatment and subsequent 4-h enzymatic saccharification with an enzyme cocktail of cellulase and amyloglucosidase. The recovery of glucose and fructose exhibited good correlation with the amounts of soft carbohydrates. The maximum yields of glucose and fructose in the rice straw per dry weight at the heading stage and the mature stage were 43.5% in cv. Habataki and 34.1% in cv. Leafstar. Thus, rice straw with soft carbohydrates can be regarded as a novel feedstock for economically feasible production of readily-fermentable glucose and fructose for bioethanol.