Transformation of Corn Stalk Residue to Humus-Like Substances during Solid-State Fermentation

Yinan Yang,Yifeng Zhang,Xintong Liu,Sen Dou,Lili Wang,Libo Li,Xuyang Shi,Xiaodong Ren

doi:10.3390/su11236771

Yinan Yang, Yifeng Zhang + Show 6 more

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https://doi.org/10.3390/su11236771

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Abstract

Lignocellulase production from straw fermentation has been widely investigated but the research has neglected to quantify fermentation-derived residue transformation to the humus-like substance (HULIS). To investigate the conversion efficacy of corn stalk residue to HULIS, the amount of HULIS associated with chemical composition and structural changes of humic acid-like substances (HAL) was investigated in a 30 L solid-state fermentation tank during a short period of eight days. The results show that the highest decomposition rate of corn stalk and the highest activity of cellulase, xylanase, and β-glucosidase appeared at the fourth day. At the end of fermenting process, the amount of humic acid-like substances (HAL) and the percentage of HAL in humus acid (PQ value) increased 17.5% and 8.9%, respectively, indicating Trichoderma reesei facilitates the transformation of corn stalk residue to HAL. Fatty acids decreased while aromatic carbon and carboxyl content significantly increased during the ongoing fermentation, which had a positive impact on the HAL thermal stability. The FTIR spectral and thermal analysis revealed an improvement in HAL degrees of condensation, oxidation, and aromatization. The present study suggests that the residue of corn stalks fermented with T. reesei might be a good fertilizer to improve soil characteristics.

Highlights

Proper management of crop residues is becoming more critical due to its high correlation with increased crop production
T. reesei (MCG77), strain purchased from American Type Culture Collection (ATCC), were inoculated on a medium containing 30 mL potato dextrose agar (PDA) and placed in an incubator at 28 ◦C for 72 hours to obtain mature mycelia; 2 mL of sterile water was added and oscillated at 130 rpm for 2 min
It was reported that cellulase activity reached the highest value in 77 hours, when the bagasse was degraded by T. reesei in solid-state fermentation [30]

Summary

Introduction

Proper management of crop residues is becoming more critical due to its high correlation with increased crop production. Due to the high reluctant content of cellulose (25%–35%), hemicellulose (20%–40%), and lignin (10%–25%) in crop residues, an effective pretreatment method is usually required in the conversion process. Monomicrobial fermentation or physicochemical microbial methods have been widely used to pretreat crop residues due to their low cost and high environmental benefits [4,5,6]. The optimal fermenting conditions of T. reesei in the biodegradation of various substrates could be different, for example, a pH of 5.0–6.6 and water content of 70%–94% for wheat bran [16] and 4% sodium hydroxide pretreatment for wheat stalks [17]. The highest cellulase activity was observed in 25–30 ◦C and a water content of 55%–70% when fermented rice bran with T. reesei [18]

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