Upstream processes of citrus fruit waste biorefinery for complete valorization

Citrus fruit waste (CW) is a useful biomass and its valorization into fuels and biochemicals has received much attention. For economic feasibility, increased efficiency of the preceding extraction and enzyme saccharification processes is necessary. However, at present, there is a lack of systematic reviews addressing these two integral upstream processes in concert for CW biorefinery. Here, the state-of-the-art advancements in enzyme extraction and saccharification processes-using which relevant essential oils, flavonoids, and sugars can be obtained-are reviewed. Specifically, the extraction options for two commercially available CW-derived products, essential oils and pectin, are discussed. With respect to enzyme saccharification, the use of an undefined commercial mixture routinely results in suboptimal sugar production. In this respect, applicable strategies for enzyme mixture customization are suggested for maximizing the hydrolytic efficiency of CW. The enzyme degradation system for CW-derived carbohydrates and its extensive application for sugar production are also discussed.

Investigation of choline chloride-formic acid pretreatment and Tween 80 to enhance sugarcane bagasse enzymatic hydrolysis

In this study, a pretreatment that consisting of choline chloride (ChCl) and formic acid (FA) were performed to improve sugarcane bagasse (SCB) enzymatic hydrolysis. Results showed that the ChCl-FA pretreatment exhibited an extraordinary ability to selectively extract hemicellulose (~95.6%) and degrade a large number of lignin (~72.6%) at 110 °C for 120 min, which enhanced the enzymatic hydrolysis of pretreated SCB. Besides, the impact of various additives on pretreated substrate enzymatic hydrolysis confirmed that Tween 80 was the best enzymatic additive, which could significantly improve the glucose produced from pretreated SCB and remarkably reduce the hydrolysis time (from 72 h to 48 h) and enzyme dosage (from 20 FPU/g pretreated solid to 10 FPU/g pretreated solid). In summary, the coupling of ChCl-FA pretreatment and Tween 80 exhibited a promising way to enhance the sugar release from SCB.

Methodology for enabling high-throughput simultaneous saccharification and fermentation screening of yeast using solid biomass as a substrate

BACKGROUND

High-throughput (HTP) screening is becoming an increasingly useful tool for collating biological data which would otherwise require the employment of excessive resources. Second generation biofuel production is one such process. HTP screening allows the investigation of large sample sets to be undertaken with increased speed and cost effectiveness. This paper outlines a methodology that will enable solid lignocellulosic substrates to be hydrolyzed and fermented at a 96-well plate scale, facilitating HTP screening of ethanol production, whilst maintaining repeatability similar to that achieved at a larger scale.

RESULTS

The results showed that utilizing sheets of biomass of consistent density (handbills), for paper, and slurries of pretreated biomass that could be pipetted allowed standardized and accurate transfers to 96-well plates to be achieved (±3.1 and 1.7%, respectively). Processing these substrates by simultaneous saccharification and fermentation (SSF) at various volumes showed no significant difference on final ethanol yields, either at standard shake flask (200 mL), universal bottle (10 mL) or 96-well plate (1 mL) scales. Substrate concentrations of up to 10% (w/v) were trialed successfully for SSFs at 1 mL volume. The methodology was successfully tested by showing the effects of steam explosion pretreatment on both oilseed rape and wheat straws.

CONCLUSIONS

This methodology could be used to replace large shake flask reactions with comparatively fast 96-well plate SSF assays allowing for HTP experimentation. Additionally this method is compatible with a number of standardized assay techniques such as simple colorimetric, High-performance liquid chromatography (HPLC) and Nuclear magnetic resonance (NMR) spectroscopy. Furthermore this research has practical uses in the biorefining of biomass substrates for second generation biofuels and novel biobased chemicals by allowing HTP SSF screening, which should allow selected samples to be scaled up or studied in more detail.

Effect of steam explosion on waste copier paper alone and in a mixed lignocellulosic substrate on saccharification and fermentation

This study evaluated steam (SE) explosion on the saccharification and simultaneous saccharification and fermentation (SSF) of waste copier paper. SE resulted in a colouration, a reduction in fibre thickness and increased water absorption. Changes in chemical composition were evident at severities greater than 4.24 resulting in a loss of xylose and the production of breakdown products known to inhibit fermentation (particularly formic acid and acetic acid). SE did not improve final yields of glucose or ethanol, and at severities 4.53 and 4.83 reduced yields probably due to the effect of breakdown products and fermentation inhibitors. However, at moderate severities of 3.6 and 3.9 there was an increase in initial rates of hydrolysis which may provide a basis for reducing processing times. Co-steam explosion of waste copier paper and wheat straw attenuated the production of breakdown products, and may also provide a basis for improving SSF of lignocellulose.

Enhanced enzymatic hydrolysis of bamboo (Dendrocalamus giganteus Munro) culm by hydrothermal pretreatment

Bamboo was non-isothermally pretreated with hot water at 140-200°C for different times (10-120 min). The effects of pretreatment conditions on the degradation of carbohydrates, cellulose crystallinity, partial removal/relocation of lignin, morphologic change of the feedstock, and glucose yield during the enzymatic hydrolysis were investigated. The effective removal of amorphous cellulose and hemicelluloses led to the increase of crystalline index of the residues. In comparison with the raw material, the surface of the pretreated samples was irregular and numerous lignin droplets appeared on the cellulose bundle surface under the intense pretreatment conditions. The glucose conversion increased with the raise of pretreatment temperature and the prolongation of time, and the maximum conversion of 75.7% was achieved for the sample pretreated at 200°C for 120 min, whereas the untreated sample was only 15.7%. The result illustrated that hydrothermal pretreatment affected the composition of bamboo, and remarkably enhanced the enzymatic hydrolysis efficiency.