Degradation of Lignin in Wheat Straw during Growth of the Oyster Mushroom (Pleurotus ostreatus) Using Off-line Thermochemolysis with Tetramethylammonium Hydroxide and Solid-State ¹³C NMR

Abstract

The oyster mushroom (Pleurotus ostreatus) is widely cultivated on wheat straw (Triticum aestivum); however, there is a need to better understand the relationship between the chemical composition of the compost and mushroom growth. Wheat straw was degraded over a period of 63 days by P. ostreatus during which time it was sampled at weekly intervals. Off-line thermochemolysis with tetramethylammonium hydroxide and solid-state (13)C NMR were then used in the molecular characterization of the undegraded wheat straw and the degraded samples. The degraded wheat straw samples had a lower proportion of syringyl- to guaiacyl-derived moieties and cinnamyl- to guaiacyl-derived moieties than the undegraded control. There were increases in both guaiacyl and syringyl acid to aldehyde ratios with composting time, which showed that side-chain oxidation has been mediated by P. ostreatus. The (13)C NMR spectra confirmed the increase in carboxyl content but indicated that the overall lignin and methoxyl contents remained relatively constant, although some nonsystematic variations were observed. The spectra also showed a decrease in amorphous noncellulosic polysaccharides in relation to the crystalline cellulose upon degradation.

Spectroscopic Characterization of Compost at Different Maturity Stages

“…Moreover, the analysis of the solid residues revealed a slightly different decomposition rate for the crystalline versus the amorphous form of cellulose fibers, as outlined by the relative decrease of the C6 peaks at 62 to 66 ppm. The uneven decrease of cellulose fibers, currently observed in the study of wood decomposition [16,21], is ascribed to the unequal porosity and exposition of glycoside subunits as well as to the various and different degrading activities of the involved enzymes [22]. Notwithstanding the exhaustive extraction of lipid components, the NMR spectra of the compost residues showed a significant permanence of alkyl compounds in the 0 to 50 ppm interval (see Fig.…”

“…3a). The former region is composed of carbons in (CH2)n-and terminal CH3 groups of plant lipid compounds, such as waxes and aliphatic biopolyesters, whereas the resonances in the O-alkyl-C region are currently assigned to monomeric units in oligo-and polysaccharidic chains of plant woody tissues [16]. Plant woody tissues were also indicated by the 57 ppm shoulder of methoxy groups on aromatic rings of guaiacyl and siringyl units of lignin structures [17].…”

A comparison of analytical techniques for evaluating food waste degradation by anaerobic digestion

“…Signals around 72-74 ppm were due to C2, C3 and C5 of cellulose as well as carbons from xylans [52]. The peak at 65 ppm may be assigned to crystalline components of C6 in hexose or C5 in pentose [53,54]. Carbohydrate structures have been reported to remain almost intact in humic and fulvic acids [50].…”

Caracterização de compostos de baixa massa molar redutores de ferro produzidos por fungos e mediação da reação de fenton para degradação de polissacarídeos e lignina

“…Esta é uma via plausível proposta há pouco mais de uma década , porém com limitada evidência da sua eficácia. O monômero altamente oxidado G6 (ácido 3,4-di-metoxi-benzóico) pode ser derivado da metilação de ácido vanílico livre, quebra de uma ligação éter do resíduo de ácido vanílico ou quebra de uma subunidade da lignina no estado intermediário de oxidação (FILLEY et al, 2000), e seu aumento em relação à madeira não degradada é interpretado como oxidação da lignina (HATCHER; MINARD, 1996;FILLEY et al, 2000;VANE et al, 2001). Assim, a oxidação da lignina em madeira pela reação de Fenton mediada por Pmp e Wc, pode, também, ser evidenciada pelas diferenças estatisticamente significativas observadas com relação ao rendimento de G6 após 13 C-TMAH termoquimólise em relação à madeira não tratada.…”

“…A relação G6/G4 (ácido/aldeído) também é geralmente mostrada em TMAH termoquimólise como um indicador do estado de degradação da lignina onde um aumento na relação G6/G4 em relação às amostras não degradadas sugere um aumento no grau de degradação da lignina (FILLEY et al, 2000(FILLEY et al, , 2002VANE et al, 2001 Quando a madeira moída foi tratada somente com CBMM ou somente com ferro e peróxido de hidrogênio, nenhuma modificação significativa em relação a madeira não tratada foi observada.…”