582 / 2018-11-12 08:27:42

Combined effect of microwave and P. chrysosporium pretreatments of distillers grains for fermentable sugars by enzymatic hydrolysis

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The liquor industry generates significant amounts of distiller’s grains in China, which is classified as lignocellulosic biomass for the production of bio-ethanol. It is because that the pretreatment of lignocellulose biomass is a critical step in the production of bio-ethanol, microwaves and P. chrysosporium pretreatments were studied to improve the yield of fermentable sugars from distiller’s grains by enzymatic saccharification in this paper. Microwave powers (0, 100, 300, 500, 700 and 900 W), microwave exposure times (0–5 min), P. chrysosporium inoculation time (2, 4, 6 and 8 min) and inoculum concentration (5, 10, 15 and 20 %) were determined by single factor and response surface methods before enzymatic hydrolysis. The results showed that optimal microwave pretreatment condition was identified as follows: microwave power of 100 W, microwave irradiation time of 3 min and solid-liquid ratio of 1:10 (g/mL). Under this condition, the yield of reducing sugar was reached to 19.74%. And on this basis, the results of combined microwaves and P. chrysosporium pretreatment could lead to a significant increase for the yield of reducing sugar to 25.21% as compared with the independent pretreatment. The Scanning electron microscopy significantly showed structural changes and the surface became increasingly coarse, the gaps between cellulose fibers were visible, and many pores were developed. Moreover, X-ray diffractometric and Fourier-transform infrared spectrometry analysis revealed that the cellulose crystallinity of pretreated distiller’s grains was changed to a different extent and the strength of characteristic peaks for corresponding typical functional groups of each component are changed compared with the feedstock. This suggests that the combination of microwave and P. chrysosporium pretreatment is effective in improving the enzymatic hydrolysis efficiency of distiller’s grains.