Enhancing the Enzymatic Saccharification of Grain Stillage by Combining Microwave-Assisted Hydrothermal Irradiation and Fungal Pretreatment

Haiwei Ren; Wenli Sun; Zhiye Wang; Shanfei Fu; Yi Zheng; Bing Song; Zhizhong Li; Zhangpu Peng

doi:10.1021/acsomega.9b03681

Enhancing the Enzymatic Saccharification of Grain Stillage by Combining Microwave-Assisted Hydrothermal Irradiation and Fungal Pretreatment

ACS Omega. 2020 May 26;5(22):12603-12614. doi: 10.1021/acsomega.9b03681. eCollection 2020 Jun 9.

Authors

Haiwei Ren¹, Wenli Sun¹, Zhiye Wang², Shanfei Fu³, Yi Zheng⁴, Bing Song⁵, Zhizhong Li¹, Zhangpu Peng²

Affiliations

¹ School of Life Science and Engineering, Lanzhou University of Technology/ Key Laboratory of Complementary Energy System of Biomass and Solar Energy, Lanzhou, Gansu Province 730050, P.R. China.
² Institute of Biology, Gansu Academy of Sciences, Lanzhou, Gansu Province 73000, P.R. China.
³ School of Environment and Civil Engineering, Jiangnan University, Wuxi, Jiangsu Province 214122, P.R. China.
⁴ Department of Grain Science and Industry, Kansas State University, 101C BIVAP, 1980 Kimball Avenue, Manhattan, Kansas 66506, United States.
⁵ Scion, 49 Sala Street, Private Bag 3020, Rotorua 3046, New Zealand.

Abstract

Grain stillage from the liquor industry was pretreated by using microwave-assisted hydrothermal pretreatment, fungal pretreatments, and their combination to enable efficient enzymatic hydrolysis for sugar production. The microwave-assisted hydrothermal (MH) pretreatment was optimized by using a response surface methodology, and the respective maximum reducing sugar yield and saccharification efficiency of 17.59 g/100 g and 33.85%, respectively, were achieved under the pretreatment conditions of microwave power = 120 W, solid-to-liquid ratio = 1:15 (g·mL^-1), and time = 3.5 min. The fungal pretreatment with Phanerochaete chrysosporium digestion (PC) achieved the maximum ligninolytic enzyme activities in 6 days with 10% inoculum size at which the reducing sugar yield and saccharification efficiency reached 19.74 g/100 g and 36.29%, respectively. To further improve the pretreatment efficiency, MH and PC pretreatments were combined, but the sequence of MH and PC mattered on the saccharification efficiency. The MH + PC pretreatment (the MH prior to the PC) was better than PC + MH (the PC prior to the MH) in terms of saccharification efficiency. Overall, the MH + PC pretreatment achieved superior reducing sugar yield and saccharification efficiency (25.51 g/100 g and 66.28%, respectively) over all other studied pretreatment methods. The variations of chemical compositions and structure features of the raw and pretreated grain stillage were characterized by using scanning electron microscopy and Fourier transform infrared spectroscopy. The results reveal that both MH and PC pretreatments mainly functioned on delignification and decreasing cellulose crystallinity, thus enhancing the enzymatic saccharification of the pretreated grain stillage. The combined MH and PC pretreatment could be a promising method to enable cost-efficient grain stillage utilization for downstream applications such as biofuels.