This paper gives an overview of the availability, nutritive quality, and possible strategies to improve the utilization of rice straw as a feed ingredient for ruminants. Approximately 80% of the rice in the world is grown by small-scale farmers in developing countries, including South East Asia. The large amount of rice straw as a by-product of the rice production is mainly used as a source of feed for ruminant livestock. Rice straw is rich in polysaccharides and has a high lignin and silica content, limiting voluntary intake and reducing degradability by ruminal microorganisms. Several methods to improve the utilization of rice straw by ruminants have been investigated in the past. However, some physical treatments are not practical because of the requirement for machinery or treatments are not economical feasible for the farmers. Chemical treatments, such as NaOH, NH 3 or urea, currently seem to be more practical for onfarm use. Alternative treatments to improve the nutritive value of rice straw are the use of ligninolytic fungi (white-rot fungi), with their extracellular ligninolytic enzymes, or specific enzymes degrading cellulose and/or hemicellulose. The use of fungi or enzyme treatments is expected to be a more practical and environmental-friendly approach for enhancing the nutritive value of rice straw and can be costeffective in the future. Using fungi and enzymes might be combined with the more classical chemical or physical treatments. However, available data on using fungi and enzymes for improving the quality of rice straw are relatively scarce.

The growing world population demands an increase in animal protein production. Seaweed may be a valuable source of protein for animal feed. However, a biorefinery approach aimed at cascading valorisation of both protein and non-protein seaweed constituents is required to realise an economically feasible value chain. In this study, such a biorefinery approach is presented for the green seaweed Ulva lactuca containing 225 g protein (N × 4.6) kg⁻¹ dry matter (DM). The sugars in the biomass were solubilised by hot water treatment followed by enzymatic hydrolysis and centrifugation resulting in a sugar-rich hydrolysate (38.8 g L⁻¹ sugars) containing glucose, rhamnose and xylose, and a protein-enriched (343 g kg⁻¹ in DM) extracted fraction. This extracted fraction was characterised for use in animal feed, as compared to U. lactuca biomass. Based on the content of essential amino acids and the in vitro N (85 %) and organic matter (90 %) digestibility, the extracted fraction seems a promising protein source in diets for monogastric animals with improved characteristics as compared to the intact U. lactuca. The gas production test indicated a moderate rumen fermentation of U. lactuca and the extracted fraction, about similar to that of alfalfa. Reduction of the high content of minerals and trace elements may be required to allow a high inclusion level of U. lactuca products in animal diets. The hydrolysate was used successfully for the production of acetone, butanol, ethanol and 1,2-propanediol by clostridial fermentation, and the rhamnose fermentation pattern was studied.

The white-rot fungi Ceriporiopsis subvermispora (Cs), Pleurotus eryngii (Pe), and Lentinula edodes (Le) have been shown to be high-potential species for selective delignification of plant biomass. This delignification improves polysaccharide degradability, which currently limits the efficient lignocellulose conversion into biochemicals, biofuels, and animal feed. Since selectivity and time efficiency of fungal delignification still need optimization, detailed understanding of the underlying mechanisms at molecular level is required. The recently developed methodologies for lignin quantification and characterization now allow for the in-depth mapping of fungal modification and degradation of lignin and, thereby, enable resolving underlying mechanisms. Wheat straw treated by two strains of Cs (Cs1 and Cs12), Pe (Pe3 and Pe6) and Le (Le8 and Le10) was characterized using semi-quantitative py-GC–MS during fungal growth (1, 3, and 7 weeks). The remaining lignin after 7 weeks was quantified and characterized using ¹³C lignin internal standard based py-GC–MS and whole cell wall HSQC NMR. Strains of the same species showed similar patterns of lignin removal and degradation. Cs and Le outperformed Pe in terms of extent and selectivity of delignification (Cs ≥ Le >> Pe). The highest lignin removal [66% (w/w); Cs1] was obtained after 7 weeks, without extensive carbohydrate degradation (factor 3 increased carbohydrate-to-lignin ratio). Furthermore, though after treatment with Cs and Le comparable amounts of lignin remained, the structure of the residual lignin vastly differed. For example, C_α-oxidized substructures accumulated in Cs treated lignin up to 24% of the total aromatic lignin, a factor two higher than in Le-treated lignin. Contrarily, ferulic acid substructures were preferentially targeted by Le (and Pe). Interestingly, Pe-spent lignin was specifically depleted of tricin (40% reduction). The overall subunit composition (H:G:S) was not affected by fungal treatment. Cs and Le are both able to effectively and selectively delignify wheat straw, though the underlying mechanisms are fundamentally different. We are the first to identify that Cs degrades the major β-O-4 ether linkage in grass lignin mainly via C_β–O–aryl cleavage, while C_α–C_β cleavage of inter-unit linkages predominated for Le. Our research provides a new insight on how fungi degrade lignin, which contributes to further optimizing the biological upgrading of lignocellulose.

The present work investigated the influence of lignin content and composition in the fungal treatment of lignocellulosic biomass in order to improve rumen degradability. Wheat straw and wood chips, differing in lignin composition, were treated with Lentinula edodes for 0, 2, 4, 8 and 12 wk and the changes occurring during fungal degradation were analyzed using pyrolysis-gas chromatography-mass spectrometry and detergent fiber analysis. L. edodes preferentially degraded lignin, with only limited cellulose degradation, in wheat straw and wood chips, leaving a substrate enriched in cellulose. Syringyl (S)-lignin units were preferentially degraded than guaiacyl (G)-lignin units, resulting in a decreased S/G ratio. A decreasing S/G ratio (wheat straw: r = −0.72, wood chips: r = −0.75) and selective lignin degradation (wheat straw: r = −0.69, wood chips: r = −0.88) were correlated with in vitro gas production (IVGP), a good indicator for rumen degradability. L. edodes treatment increased the IVGP of wheat straw and wood chips. Effects on IVGP were similar for wheat straw and wood chips indicating that lignin content and 3D-structure of cell walls influence in vitro rumen degradability more than lignin composition.

BACKGROUND: No attention has been paid so far to the preservation of fungal‐treated lignocellulose for longer periods. In the present study, we treated wheat straw (WS) with the white‐rot fungi Ceriporiopsis subvermispora and Lentinula edodes for 8 weeks and assessed changes in pH, chemical composition and in vitro gas production (IVGP) weekly. Fungal‐treated WS was also stored for 64 days ‘as is’, with the addition of lactic acid bacteria (LAB) or with a combination of LAB and molasses in airtight glass jars mimicking ensiling conditions.RESULTS: Both fungi significantly reduced the lignin and hemicellulose content of WS, and increased the cellulose content. The IVGP increased with increasing time of incubation, indicating the increase in digestibility. Both fungi lowered the pH of WS under 4.3, which guarantees an initial and stable low pH during anaerobic storage. Minor changes in fibre composition and IVGP were observed for stored L. edodes treated WS, whereas no change occurred for C. subvermispora.CONCLUSION: It is possible to conserve C. subvermispora and L. edodes treated straw under anaerobic condition without additives up to 64 days. This finding is important for practical application to supply fungi‐treated feed to ruminant animals for a prolonged period. © 2017 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.