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The production of fermentable sugars from rice hull was studied by dilute acid pretreatment and enzymatic saccharification. Rice hull (15%, w/v) was pretreated by 1% (v/v) sulfuric acid at high temperature (120 approximately 160 degrees C) for 15, 30, 45, and 60 min, respectively. The maximum sugar concentration from rice hull in the prehydrolysate was obtained at 140 degrees C for 30 min, but the enzymatic saccharification yield from the corresponding pretreated rice hull is not high. To another aspect, the maximum enzymatic saccharification yield was achieved at 160 degrees C for 60 min, while the recovery of fermentable sugars was the poorest. To take account of fermentable sugars from pretreatment and enzymatic saccharification, the maximum yield of sugars was obtained only when rice hull was treated at 140 degrees C for 30 min. Under this condition, 72.5% (w/w) of all sugars generated from the raw material can be recovered. The kinetic study on the enzymatic saccharification of dilute acid pretreated rice hull was also performed in this work by a modified Michaelis-Menten model and a diffusion-limited model. After calculation by a linear and a non-linear regression analysis, both models showed good relation with the experimental results.

In this study, a process of removing a half volume of culture broth and replacing it with an equal volume of substituted solution was developed to enhance the production of heteropolysaccharide-7 (PS-7) by Beijerinckia indica HS-2001. The optimal substitution time and volume of the substituted solution were found to be 48 h after cultivation and 50% of the initial volume of the culture broth. The optimal composition of the substituted solution was determined to be 20.0 g/L glucose, 10.0 g/L soybean pomace, 0.1 g/L MgSO 4 ·7H 2 O, 0.9 g/L NH 4 NO 3 , and 5.0 g/L potassium phosphate, which was the same composition as the medium developed in a previous study for the production of PS-7 by B. indica HS-2001. The total amount and productivity of PS-7 by B. indica HS-2001 with a substitution under optimized conditions in a 7 L bioreactor for 96 h were 49.28 g and 0.51 g/h, respectively, which were 1.76 and 1.31-foldgreater values than those without a substitution for 72 h.

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