Abstract
BackgroundEnergy crops including Miscanthus provide a storable, portable energy source which can be used to complement a wide range of products and energy generation systems. Miscanthus is predominantly used in Europe as a combustion material for electricity generation but also has the potential for biochemical conversion due to its high yield and low-nutrient requirements. The ratio of holocellulose (hemicellulose and cellulose combined) to acid detergent lignin (H:L) within the senesced material has previously been shown to indicate the relative suitability of Miscanthus accessions for thermochemical conversion. In this study, the ratio was assessed to examine its use as a selection aid for biochemical conversion. 20 highly-characterised Miscanthus accessions were saccharified using an enzyme mix to determine optimum sugar release. Nine of these accessions spanning high, medium and low H:L ratios were then autoclaved with dilute acid, alkali or water, and enzymically hydrolysed and fermented to produce ethanol. Samples taken throughout the process allowed assessments of released sugars.ResultsEnzymic degradation of the biomass showed a relationship between H:L ratio and glucose release, with high glucose release for high H:L ratio accessions and vice versa. Xylose release showed no such relationship. This relationship was maintained following pretreatments and enzyme saccharification, where compound analysis showed that following all pretreatments, accessions with high H:L ratios repeatedly had the highest releases of glucose, xylose and arabinose, and produced more ethanol. Release of all measured compounds increased with the pretreatment severity and ethanol yields from each pretreatment correlated with the respective glucose yield, providing assurance that any inhibitory compounds generated were tolerated by the fermentation yeast. Strong correlations were also seen between glucose release, ethanol and cell wall components, with cellulose showing the highest correlations with ethanol yields for some treatments and H:L ratio with others.ConclusionsThe H:L ratio is a good predictor of ethanol yields and sugar release from Miscanthus in this study but individual components lignin and cellulose also correlate well, especially for hot water and mild acid pretreatments. In conclusion, use of the H:L ratio does not provide any advantages over the concentration of individual cell wall components for predicting sugar release and ethanol yields.
Highlights
Energy crops including Miscanthus provide a storable, portable energy source which can be used to complement a wide range of products and energy generation systems
A number of analyses have previously been conducted on this material including Neutral Detergent Fibre (NDF), Acid Detergent Fibre (ADF) and Acid Detergent Lignin (ADL), which with ash measurements informed on the proportion of hemicellulose, cellulose and lignin present in each sample [3]. 20 Miscanthus genotypes were selected from these accessions using this available composition data and randomly designated 1–20
No pretreatment saccharification assay Each bag containing a non-pretreated Miscanthus accession replicate was sampled four times, with two technical replicates incubated with additional enzymes and two technical replicates incubated without as controls
Summary
Energy crops including Miscanthus provide a storable, portable energy source which can be used to complement a wide range of products and energy generation systems. 20 highly-characterised Miscanthus accessions were saccharified using an enzyme mix to determine optimum sugar release Nine of these accessions spanning high, medium and low H:L ratios were autoclaved with dilute acid, alkali or water, and enzymically hydrolysed and fermented to produce ethanol. One source of biomass is the ‘energy crops’, high-yielding crops with low moisture content at harvest [1], which grow well on sub-optimal land with low fertiliser demands [2] Within these requirements, the perennial grasses from Asia in the genus Miscanthus [3] have been identified as an energy crop with global potential [2], with some M. sinensis hybrids producing up to 41 t Ha−1 yr−1 [4]. This produces a feedstock with more desirable biomass processing properties such as a lower reactive alkali metal content and a reduced drying requirement [7], despite a concurrent yield loss compared to peak yield attributed to leaf loss [5], with leaves contributing approximately one-third of the total biomass in Miscanthus [8]
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