Abstract:

The primary aim of this study is to optimize the process of cellulose degradation of distiller's grains. Utilizing discarded distiller's grains from liquor and rice wine factories for NaOH pretreatment, this research conducted a univariate experiment to investigate the impacts of NaOH concentration, distiller's grain particle size and NaOH treatment duration on the cellulose content in the grains. The distiller's grains and the optimal pretreatment conditions were selected based on the experimental results. Subsequently, cellulase was used for enzymatic hydrolysis, and the effects of enzyme dosage, hydrolysis temperature, and hydrolysis time and pH value on the enzymatic hydrolysis of distiller's grains cellulose were studied. A response surface analysis of three-level, four-factor was performed with reducing sugar absorbance as the response variable to determine the optimal conditions for enzymatic hydrolysis. The results showed that: (1) in the pretreatment test, different NaOH concentration and NaOH action time had significant effects on cellulose content of the same distillers, but mesh number had no significant effects on cellulose content of distillers. Under the same treatment conditions, the cellulose content of liquor distiller's grains was significantly higher than that of rice wine distiller's grains. Considering these factors, liquor distiller's grains were selected for subsequent enzymatic hydrolysis experiments. (2) The single-factor of the enzymatic hydrolysis process showed that the optimal effects of enzyme dosage, hydrolysis temperature, hydrolysis time, and pH were 800 U/g, 50℃, 4.5 h, and pH 5.5, respectively. Based on the single-factor results, a four-factor and three-level response surface analysis was conducted, which showed that enzyme dosage, temperature, and time had significant effects on the absorbance of reducing sugar, while pH had no significant effect. Among the pairwise interactions, enzyme dosage with time and temperature with time had significant effects on the absorbance of reducing sugar. The regression relationship between these four factors and the absorbance was significant and well-fitted, which could be used for prediction in actual production. The optimal hydrolysis conditions were as follows: cellulase dosage of 950 U/g, reaction temperature of 48℃, reaction time of 5.1 hours, and pH 5.5. Under these conditions, the maximum absorbance reached 0.47. This study indicates that through proper pretreatment and enzymatic hydrolysis, the cellulose in distillers' grains can be effectively converted into reducing sugars, offering a viable approach for the high-value utilization of distillers' grains.

Key words: distillers’grains, cellulose, NaOH pretreatment, enzymatic hydrolysis, response surface analysis, reducing sugars, absorbance