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Hydrolytic conditions of rice hulls by acid and alkaline treatments before enzymatic saccharification were optimized in this study. Based on the results of single-factor experiments and an orthogonal array experiment, reaction time was found to be the most important factor for the acidic hydrolysis of rice hulls. Maximum yield of sugars from 1 g of rice hulls by acidic treatment under optimized conditions was 213.6 mg. The yield of lignin removal from acidic pretreated rice hulls by alkaline treatment increased with increase in reaction temperature and time. The amount of sugars obtained from 1 g of pretreated rice hulls by enzymatic saccharification was 307.7 mg, and the conversion rate of sugars from crude fibers in pretreated rice hulls was about 72%. Instrumental analyses with FTIR and SEM indicated that lignin in rice hulls was partially removed by alkaline treatment, and the structure of rice hulls became deformed and more fibers were exposed to cellulases after acidic treatment.

The present study investigated the effects of three constituent amino acids on glutathione production in flask culture of Candida utilis. Although l-glutamic acid and glycine had little impact on cell growth and glutathione biosynthesis, l-cysteine positively influenced glutathione production, despite inhibiting cell growth when it was added prior to stationary phase. Adding 8 mmol/L of l-cysteine to the culture broth at 16 h boosted glutathione production by 91%, increasing the intracellular glutathione content by 106% compared to untreated controls. A temperature-shift strategy, in which we shifted batch and fed-batch cultures of C. utilis from 30 to 26°C, also significantly enhanced glutathione production. Applying both strategies (i.e. adding 20 mmol/L l-cysteine and shifting the temperature from 30 to 26°C) at 33 h enhanced the glutathione concentration and the intracellular glutathione content to 1,312 mg/L and 3.75%, respectively, during fed-batch cultivation (glucose feeding at a constant rate of 18.3 g/h). The average specific glutathione production rate under this condition was 129% higher than that of the control without strategy.