Saakshi Bangera, DY Patil School of Biotechnology and Bioinformatics
There is a crucial need for ecologically friendly alternatives for petroleum-derived products. Forest, as well as agricultural industries, are adopting clean technologies that will transform sustainable resources into bio-based products of high economic value. One of the majorly underused biomass components is xylans – an important asset for sustainable product development.
Xylan comprises β-d-xylopyranosyl (Xylp) monomers and is divided into either homoxylan or heteroxylan. Heteroxylans are the major form of hemicellulose in land-dwelling plants. In hardwoods, heteroxylans account for 10-35% of the total dry weight and in softwoods, this value is up to 10%. Xylan-rich portions generated by forestry industries are often unused or recovered for energy, whereas those generated by agricultural industries are used in low-animal feed. Enzymatic conversion of xylans to fermentable sugars has been highly studied. The enzymatic discoveries that modify xylan structures open new options to upgrade their use beyond industrial chemicals.
The diverse chemistry of heteroxylans:
Heteroxylans are categorized into three main types
- Glucuronoxylans
- Arabinoxylans
- Glucuronoarabinoxylans
Glucuronoxylans are commonly present in hardwoods and are substituted with acetyl groups. Numerous extraction methods have been developed to isolate xylans from agricultural and wood fibre. These methods include alkali extraction, ionic liquid extraction, hot water extraction, organic solvent extraction, and steam explosion. Pre-extraction of xylan before pulping poses an advantage to the pulping process. Organic solvent extraction can recover xylans with high uronic acids. The intended end use of isolated xylans dictates the choice of an appropriate isolation method.
Heteroxylans bring multiple opportunities:
Current practices use pre-extraction methods from forest and agricultural residues to recover xylans. The corresponding xylose is then converted to furfural and xylitol. Furfural has a wide range of applications and xylitol is mainly used as an alternative sweetener and preservative. Due to the properties of low oxygen permeability, aroma permeability, and high light transmittance, xylans are used to prepare films and hydrogels for drug delivery and food packaging.
Enzymatic upgrading of xylans:
A significant approach to alter the physicochemical properties of xylan-based films is to debranch xylans without degrading the main xylan chain. Novel xylan-active enzymes are used for the enzymatic upgrading of xylans. For instance, enzymes that introduce carbonyls at C2 or C3 positions of the xylose backbone, allow the formation of intra-chain and inter-chain hemiacetals. This formation stabilized hydrogels.
Technology for xylan-based polymers:
By enzymatic controlling of Araf: Xylp ratio of arabinoxylan, custom-made films can be created. The ability of xylans to adsorb onto cellulosic surfaces renders them suitable for producing biocomposite materials. For instance, the addition of softwood and hardwood xylans to cellulose hydrogels increases its elongation under the tension of corresponding composites.
Conclusion:
Xylans are often underused in current biorefinery processes. Increasing the use of components of forestry and agricultural feedstocks while reducing waste has maximized interest in upgrading xylans. Chemical approaches are available that convert xylans into biochemicals and functional polymers. Xylan-based polymers are majorly used in food coating, food packaging, and drug delivery, etc. However, to expand its applications enzymatic approaches are preferred. Glycoside hydrolase, carbohydrate esterase, and oxidoreductase enzymes provide the machinery to modify the properties of xylan-based hydrogels and films.
Engineering enzymes that stabilize xylan-based hydrogels offer new tools to expand bio-based materials from polymeric xylans. The combination of xylan extraction with other biorefinery processes could be economically beneficial when degraded xylan fractions are also valorized. There is a critical need for techno-economic assessments for the enzymatic upgrading of xylans from different sources.
Also read: Corneal collagen cross-linking – a new way to treat keratoconus
Reference:
- Vuong, T. V., & Master, E. R. (2022). Enzymatic upgrading of heteroxylans for added-value chemicals and polymers. Current Opinion in Biotechnology, 73, 51–60. https://doi.org/10.1016/j.copbio.2021.07.001
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Author info:
Saakshi Bangera is currently pursuing MSc. in Biotechnology from DY Patil School of Biotechnology and Bioinformatics. She believes that she doesn’t have a specific area of interest yet. She wishes to explore toxicology and food biotechnology. She’s quite passionate about Biotechnology and aims to grab every opportunity she comes across.
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