Structural carbohydrates in a plant biomass: correlations between the detergent fiber and dietary fiber methods

Development of a protocol for fractionating and characterising fibres from lignocellulosic food waste

This study aims to explore an advanced protocol for characterising dietary fibre (DF) fractions to meet the growing demand for accurate and reliable data. Although current enzymatic-gravimetric approaches, e.g., AOAC and Van Soest analysis, provide information about soluble and insoluble DF quantification, they present limitations related to the lack of fractions characterisation. To overcome these limitations, the proposed protocol integrates the official AOAC 991.43 method with the sequential fibre fractionation by exploiting the different resistance of the fibre fractions to acid hydrolysis treatments (TFA and H2SO4), utilising hazelnut shells as a case-study. Each hydrolysed fraction was quantified and characterised through GC-MS analysis of monosaccharides. The data obtained for hemicellulose, cellulose, and lignin fractions were then discussed and compared with the Van Soest method. This approach yields a comprehensive procedure applicable to different food and nutraceutical products, emphasising the importance of DF characterisation for a deeper understanding of their bio-functional properties.

Aquatic weeds as novel protein sources: Alkaline extraction of tannin-rich Azolla

The aquatic weed Azolla is a potential protein crop due to its prolific growth and high protein content, supported entirely by nitrogen-fixing symbionts. Alkaline protein extraction at pH 8 followed by acid precipitation allowed recovery of 16-26% of the biomass nitrogen, while at pH 10.5 nitrogen recovery improved to 35-54%. This pH effect was typical of ferns of the family Salviniaceae, and may be explained by high concentrations of condensed tannins (CTs) in the biomass that precipitate protein at mild pH. Two approaches were tested to increase protein yield and reduce protein binding by CTs. Pre-extraction with aqueous acetone (70 v/v%) removed 76-85% of the CTs and subsequent alkaline extraction at pH 12.5 and 95 °C recovered 38% of the biomass nitrogen. Extraction with 1.5% of PEG as a CT-binding agent, also permitted to recover 38% of the nitrogen, under milder conditions of pH 8 and 45 °C.

Selective ligninolysis of wheat straw and wood chips by the white-rot fungus Lentinula edodes and its influence on in vitro rumen degradability

BACKGROUND

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.

RESULTS

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.

CONCLUSIONS

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.

The effect of particle size and amount of inoculum on fungal treatment of wheat straw and wood chips

Background

The aim of this study was to optimize the fungal treatment of lignocellulosic biomass by stimulating the colonization. Wheat straw and wood chips were treated with Ceriporiopsis subvermispora and Lentinula edodes with various amounts of colonized millet grains (0.5, 1.5 or 3.0 % per g of wet weight of substrate) added to the substrates. Also, wheat straw and wood chips were chopped to either 0.5 or 2 cm. Effectiveness of the fungal treatment after 0, 2, 4, 6, or 8 wk of incubation was determined by changes in chemical composition, in vitro gas production (IVGP) as a measure for rumen degradability, and ergosterol content as a measure of fungal biomass.

Results

Incomplete colonization was observed for C. subvermispora treated wheat straw and L. edodes treated wood chips. The different particle sizes and amounts of inoculum tested, had no significant effects on the chemical composition and the IVGP of C. subvermispora treated wood chips. Particle size did influence L. edodes treatment of wheat straw. The L. edodes treatment of 2 cm wheat straw resulted in a more selective delignification and a higher IVGP than the smaller particles. Addition of 1.5 % or 3 % L. edodes inoculum to wheat straw resulted in more selective delignification and a higher IVGP than addition of 0.5 % inoculum.

Conclusion

Particle size and amount of inoculum did not have an effect on C. subvermispora treatment of wood chips. At least 1.5 % L. edodes colonized millet grains should be added to 2 cm wheat straw to result in an increased IVGP and acid detergent lignin (ADL) degradation.

Improved sugar yields from biomass sorghum feedstocks: comparing low-lignin mutants and pretreatment chemistries

BACKGROUND

For biofuel production processes to be economically efficient, it is essential to maximize the production of monomeric carbohydrates from the structural carbohydrates of feedstocks. One strategy for maximizing carbohydrate production is to identify less recalcitrant feedstock cultivars by performing some type of experimental screening on a large and diverse set of candidate materials, or by identifying genetic modifications (random or directed mutations or transgenic plants) that provide decreased recalcitrance. Economic efficiency can also be increased using additional pretreatment processes such as deacetylation, which uses dilute NaOH to remove the acetyl groups of hemicellulose prior to dilute acid pretreatment. In this work, we used a laboratory-scale screening tool that mimics relevant thermochemical pretreatment conditions to compare the total sugar yield of three near-isogenic brown midrib (bmr) mutant lines and the wild-type (WT) sorghum cultivar. We then compared results obtained from the laboratory-scale screening pretreatment assay to a large-scale pretreatment system.

RESULTS

After pretreatment and enzymatic hydrolysis, the bmr mutants had higher total sugar yields than the WT sorghum cultivar. Increased pretreatment temperatures increased reactivity for all sorghum samples reducing the differences observed at lower reaction temperatures. Deacetylation prior to dilute acid pretreatment increased the total sugar yield for all four sorghum samples, and reduced the differences in total sugar yields among them, but solubilized a sizable fraction of the non-structural carbohydrates. The general trends of increased total sugar yield in the bmr mutant compared to the WT seen at the laboratory scale were observed at the large-scale system. However, in the larger reactor system, the measured total sugar yields were lower and the difference in total sugar yield between the WT and bmr sorghum was larger.

CONCLUSIONS

Sorghum bmr mutants, which have a reduced lignin content showed higher total sugar yields than the WT cultivar after dilute acid pretreatment and enzymatic hydrolysis. Deacetylation prior to dilute acid pretreatment increased the total sugar yield for all four sorghum samples. However, since deacetylation also solubilizes a large fraction of the non-structural carbohydrates, the ability to derive value from these solubilized sugars will depend greatly on the proposed conversion process.

Biochemical methane potential prediction of plant biomasses: Comparing chemical composition versus near infrared methods and linear versus non-linear models

The reliability of different models to predict the biochemical methane potential (BMP) of various plant biomasses using a multispecies dataset was compared. The most reliable prediction models of the BMP were those based on the near infrared (NIR) spectrum compared to those based on the chemical composition. The NIR predictions of local (specific regression and non-linear) models were able to estimate quantitatively, rapidly, cheaply and easily the BMP. Such a model could be further used for biomethanation plant management and optimization. The predictions of non-linear models were more reliable compared to those of linear models. The presentation form (green-dried, silage-dried and silage-wet form) of biomasses to the NIR spectrometer did not influence the performances of the NIR prediction models. The accuracy of the BMP method should be improved to enhance further the BMP prediction models.