Trichoderma sp. AH pretreatment improves organic oxygen composites from supercritical alcoholysis of wheat straw

TL;DR

This study shows how pretreating wheat straw with Trichoderma sp. AH affects the types of organic oxygen compounds produced during alcoholysis, which could be useful for biofuel production.

Contribution

The novelty lies in using Trichoderma sp. AH pretreatment to alter the composition of organic oxygen composites in supercritical alcoholysis of wheat straw.

Findings

OOCs with O5 and O4 were the most prominent in the methanol-soluble fraction of original and pretreated wheat straw, respectively.

Trichoderma sp. AH pretreatment influenced the specificity and transformation of OOCs during supercritical alcoholysis.

The study provides insights into using MSF for fuel source production.

Abstract

Electrospray ionization fourier transform ion cyclotron resonance mass spectrometry was applied to evaluate the organic oxygen composites (OOCs) in methanol fraction derived from the supercritical alcoholysis of original and pretreated straw (WS) utilizing Trichoderma sp. AH. In the methanol-soluble fraction (MSF) of untreated and preconditioned WSs, On (n =  1–10), with double bond similar values of 1–28 and carbon atom numbers of 4–35, was the most predominant OOCs in the negative ion mode. O5 and O4 were the most prominent OOCs in the MSF of original and preconditioned WS, respectively. These results assist in comprehending the impact of Trichoderma sp. AH pretreatment on the specificity, and transformation of OOCs in WS alcoholysis and the application of MSF to manufacture fuel source.

Figures

Mass spectra of MSF0 and MSF5 with analysis of negative ion ESI FT–ICR MS.

MM arrangement of compounds with analysis of negative ion ESI FT–ICR MS in MSF0 and MSF5.

RCs of N0On and N1On species in MSF0and MSF5 with analysis of negative ion ESI FT–ICR MS.

Isoabundance plots of DBE versus CAN for species O1 to O5 in MSF0 and MSF5 with analysis of negative ion ESI FT–ICR MS. The main blue–grey cycle has been replaced with grey because the relative abundance of the main blue–grey plot is so high that the size is out of frame.

Isoabundance plots of DBE versus CAN for species O6 to O10 in MSF0 and MSF5 with analysis of negative ion ESI FT–ICR MS.

Full text

1. Introduction

Low efficiency and specificity and low relative contents of products have limited the application of bio-oils from themolysis [1–3]. Pretreatment (PT) could decompose or disintegrate cellulose, hemicellulose, or lignin and their crystallization for efficient preparation of biomass themolysis [4–6]. Moreover, bio-pretreatment has been found to be able to enhance enzymatic scarification because of its low energy consumption, inexpensive, low reliance on chemicals, and friendly environmental factor [7–11].

So far, there are still few reports on application of fungi to promote the transformation of biological treated materials’ liquefaction, involving rice straw (RS), wheat straw (WS), soybean straw, switch grass, hardwood, and corn straw. In our previous research [12–15], supercritical alcoholysis of RS and WS could be promoted with PT utilizing Trichoderma sp. AH in their transformation, specially esters in methanol-soluble fraction (MSF) of WS and RS. Nevertheless, less than one hundred organic composites were identified in MSF with GC-MS. Moreover, FT-ICR-MS analysis showed that PT using Trichoderma sp. AH could promotes directional transformation of organic oxygen composites (OOCs) and organic nitrogen composites in supercritical alcoholysis of RS and the richness of O4 and N2O4 species in MSF could be enhanced.

In our current study, to determine effect of PT using Trichoderma sp. AH on OOCs produced by supercritical alcoholysis original and preconditioned WS. The FT-ICR-MS was used to analyze the MSFs of the two materials. The aim was to comprehend effect of Trichoderma sp. AH pretreatment on transformation of OOCs in MSF from supercritical alcoholysis of WS and the application of MSF in the manufacturing of fuel source.

2. Methods

2.1. PT of WS

WS were collected in a farm close to Yunlong District in Xuzhou, Jiangsu, China, and processed by Trichoderma sp. AH using techniques described in our earlier studies [12–14]. Every single one of the analytical reagents utilized as solvents had been previously purified through distillation.

2.2. Alcoholysis of WS

WS alcoholysis was carried out by the procedure outlined in our earlier investigations [12–14]. The approach utilized in our earlier research was utilized to calculate the outputs of gas, MSFs, and residues [12–14]. Each experiment was operated three times in order to demonstrate that the error was less than ± 5%.

2.3. ESI-FT-ICR-MS analysis

MSFs were determined with a Bruker apex-ultra FT-ICR MS, and detailed data was obtained by Bruker software with the method described in our earlier investigations [13,14]. Each analysis was circulated three times or more to demonstrate that the error was less than ±  5% in the relative content (RCs) of the composites found.

3. Results and discussion

For ease of description, MSF_5_ and MSF_0_ are utilized to denote MSF from supercritical alcoholysis of WS_5_ and WS_0_, respectively. In our earlier study [15], the highest MSF_5_ and MSF_0_ yields were 38.3% and 24.6%, respectively. The overall RCs of OOCs in MSF_0_ and MSF_5_ were 92.4% and 96.2%, respectively. As a result, negative ion ESI-FT-ICR-MS was utilized to examine the OOCs in MSF_0_ and MSF_5_, respectively.

3.1. Analysis of OOCs in MSF by negative ion ESI-FT–ICR-MS

MSFs had molecular masses (MMs) ranging from m/z 100 to 500, as illustrated in Fig 1. Observed compositions are O1–O10 and N1O0–N1O9, respectively. The masses observed for OOCs have relatively minor uncertainties in theoretical masses. According to Fig 2, the majority of MMs in MSF_5_ and MSF_0_ are distributed between 300 and 450 u. In comparison to MSF_0_, MSF_5_ has more relative abundances (RAs) for MMs arranged from 300 to 350 u.

Mass spectra of MSF0 and MSF5 with analysis of negative ion ESI FT–ICR MS.

MM arrangement of compounds with analysis of negative ion ESI FT–ICR MS in MSF0 and MSF5.

On the basis of precise mass-to-isotope mass ratios, more than 95% of the mass spectral peaks (Fig 1) could be attributed. Ascribed elemental compositions are categorized on the basis of double bond equivalent (DBE), carbon atom number (CAN), and hetero-atom number (HAN) of our prior studies. All allocated elemental compositions are divided into the following groups: On (DBE =  1–26, CAN =  4–38), N_1_O_n_ (DBE =  1–22, CAN =  4–31), including O1–O_10_ and N1O0–N1O9 species. The O4 species are the most prevalent in MSF_5_, but the O5 species are the most prevalent species in MSF_0_, as revealed in Fig 3. The RCs of On species in MSF_5_ are 92.0%, and that of MSF_0_ are 91.3%. The distinct MMs distribution in MSF_5_ and MSF_0_ may be due to the diverse distribution of On in MSF_5_ and MSF_0_. These results indicate that the On species is the dominant compound in MSF and that its RC is significantly greater than that of the N1On species.

RCs of N0On and N1On species in MSF0and MSF5 with analysis of negative ion ESI FT–ICR MS.

3.1.1. O

1 and O 2 species.

The pattern of On in MSF_0_ is identical to that of DBE =  1–28 and CANs =  4–38 in MSF_5_, which is equivalent to the RS that we previously analyzed, as shown in Figs 4 and 5 [14].

Isoabundance plots of DBE versus CAN for species O1 to O5 in MSF0 and MSF5 with analysis of negative ion ESI FT–ICR MS. The main blue–grey cycle has been replaced with grey because the relative abundance of the main blue–grey plot is so high that the size is out of frame.

Isoabundance plots of DBE versus CAN for species O6 to O10 in MSF0 and MSF5 with analysis of negative ion ESI FT–ICR MS.

As shown in Fig 4, O1 species in MSF_5_ have DBEs and CANs ranging from 2 to 28 and 5 to 33, respectively, while those in MSF_0_ have DBEs ranging from 1 to 26 and CANs ranging from 6 to 38. As shown in Figs 2 and Fig 5, O1 with DBE = 10 in MSF_0_ has the highest RA, about five times that of MSF_5_, while other O1 species in MSF_0_ have relative abundances largely similar to those in MSF_5_. Most O1 species are supposed to be alkylphenols [16–18]. Alkylphenols with CAN = 15–20 are believed to be O1 species with DBE = 4 in O1, and O1 species with DBE = 5, 8, and 12 are supposed to be cyclohexylphenol (C_12_–C_20_), biphenyl alcohol (C_16_–C_22_) and triphenyl alcohol (C_18_–C_23_), respectively. In addition, the species in the O1 category with CANs <  18 are supposed to be biphenyl alcohols with DBE =  9, and the others are supposed to be cyclohexyl biphenyl alcohols.

The DBE and CAN for the O2 species in MSF_5_ are 2–22 and 6–35 respectively, while the DBE =  1–22 and CAN =  4–35 in MSF_0_ have similar ranges (Fig 4). As shown in Fig 2 and Fig 4, the highest RA for the O2 species in MSF_0_ is at DBE =  5 and CAN =  27, which is twice as high as in MSF_10_. Also, similar to the O1 species, the O2 species in MSF_0_ has an RA at DBE =  10 which is approximately five times higher than that of MSF_5_. A range of O2 species can be perceived at DBE =  7–11 and CAN =  8–22. The alkanoic (DBE = 1), alkenoic (DBE = 2), and alkydioic (DBE = 3) acids, which mostly correspond to stearic, hexadecanoic, and octadecadienoic acids, are thought to constitute the O2 species at DBE =  1–3.

3.1.2. O

3–O 10.

The majority of species in the O3–O10 classes with DBE = 1–3 are supposed to be attributed to derivatives of sugar compounds [19–21], which are produced by the decomposition of cellulose or hemicellulose. As depicted in Fig 3 and Fig 4, most O3 species in MSF_5_ and MSF_0_ have CANs =  5–30 and DBE =  2–20 with the maximum RA composites in MSF_5_ having DBE = 7 and CAN = 19, about 4 times greater than in MSF_0_. Species with DBE >  3 in the O3 classes should have p–coumarin, coniferin, and sinapin structures, which are derived from lignin. Most O4 classes have DBE = 2–15 and CANs = 5–30, with the highest RA composites in MSF_5_ having DBE = 2 and CAN = 16, about 20 times than in MSF_0_. Based on the extents of DBE and CAN of 4–8 and 17–30 respectively, the O4 species are supposed to be Alkylphenols and esters with one or two benzene rings. The distribution and range of DBE and CAN values for the O5 species in MSF_0_ are similar to those in MSF_5_. The distribution and range of DBE and CAN in O6–O10 in MSF_5_ are also comparable to that in MSF_0_, as shown in Fig 5. With the addition of oxygen atoms, sugars become the predominant species in O5–O10.

Species with DBE = 1–3 in O2–O7 are equally numerous as that with DBE = 4–15, as seen in Figs 4 and 5. According to our prior research [14], Most of MSFs-associated acidic species are likely lignin-derived compounds, according to the comparatively high RCs in O2–O9 for DBE = 5–10 (Fig 3). Furthermore, the high RCs in O3–O10 for DBE = 1–4 suggest that the other main MSFs-associated acidic species are molecules generated from hemicellulose, and cellulose particularly sugars.

While the RCs of O5–O10 in MSF_5_ is distinct from that of MSF_0_ (Fig 3), the arrangement and range of DBE values and CAN are similar for MSF_0_ and MSF_5_, while the RCs and distribution of O1–O4 for MSF_0_ and MSF_5_ are different. As revealed in Fig 2, there are differences in the MM arrangements between MSF_0_ and MSF_5_, specially from 300 to 350 u. The greatest values of RC for the O4 species with DBE = 2 in MSF_5_ are much greater than those in MSF_0_, while the maximum RC values for the O1 and O2 species with DBE = 10 in MSF_5_ are lesser than those in MSF_0_ as indicated in Fig 3. These results imply that WS with BPT is inclined to be changed to O4 species through supercritical alcoholysis of WS.

PT increases the yield of OOCs and enriches O4 species in the MSF of supercritical alcoholysis feedstock and preconditioned WS. The enhancement was mainly due to structural changes in WS through PT due to incomplete decomposition with enzymes, e.g., ligninase, hemi cellulase, and cellulase. In our earlier research [15], PT utilizing Trichoderma sp. AH slightly altered the elemental and chemical composition of WS, and there was no significant difference in the content of the main constituents (lignin, hemicellulose, and cellulose) in original and preconditioned WS. FTIR spectra of the original and preconditioned WS showed little significant changes in bands’ spectral profiles and relative strengths, representing that lignin, hemicellulose, and cellulose were still pertain in the preconditioned WS and none of these main components disappeared considerably after preconditioning with Trichoderma sp. AH. SEM analysis exhibited that PT utilizing Trichoderma sp. AH caused prominent intrusion of gaps’ structure and formation. The structures of WS, such as lignin, hemicellulose, and cellulose, were incompletely broken down by enzymes such as ligninase, hemi cellulase, and cellulase (manganese peroxidase, laccase, and lignin peroxidase) into mono-polymers or short oligomers, so that de-polymerization and re-polymerization of hemicellulose, and cellulose with methanol can be conceded out efficiently, and easily, leading to an increased yield of OOCs and an enrichment of O4 species in MSFs.

3.2. Enlightened conception for efficient MSF transformation

As OOCs present in MSFs have been revealed with NIFTICRMS and they are provocative and unstable, these OOCs must been taken off or transformed when MSFs are utilized to manufacture commercial fuels. Catalytic hydro-deoxygenation and hydro-transformation are perceived to be effectient methods for superordinating Bio-oils [22–24]. A maximum of the oxygen in MSFs can be detached by catalytic hydro-deoxygenation and can be easily eliminated, while most of the nitrogen in MSFs can be easily removed by catalytic hydro-transformation. The catalytic hydro-transformation and hydro-deoxygenation of MSFs can be facilitated by biomass alcoholysis, and knowledge of the morphology of MSFs can be useful in choosing or developing effective catalysts to improve MSFs. Thus, the mixture of bio-reprocessing, alcoholysis, hydro-transformation, and catalytic hydro-deoxygenation may benefit the transformation of biomass and the application of MSFs in transport fuel production.

4. Summary

The range of OOCs in MSFs according to the MM distribution was from 100 to 500 u, with the majority of 300–450 u. In MSFs of raw and preprocessed WSs, are On (n =  1–10), DBE (n = 1–28), and CAN (n = 4–35) are the most prevalent OOCs. The most prominent OOCs in MSFs of unprocessed and preprocessed WSs are O5 and O4, respectively. In the supercritical alcoholysis of WS, PT utilizing Trichoderma sp. AH raised the specificity and transformation of OOCs, encouraging the concentration of O4 species in MSFs. These results help to understand how Trichoderma sp. AH’s PT affects the specificity, transformation, and use of OOCs in the supercritical alcoholysis of WS and the manufacture of fuel sources.