Plant biomass, which is the main source of renewable materials on earth, consists largely of two polysaccharides (cellulose and hemicelluloses) and an aromatic polymer (lignin). In hardwood species, grasses and agro-industrial by-products xylans are the most abundant hemicelluloses. Xylan is built from a backbone of β-1,4-linked xylose units with diverse substituent decorations depending on the raw material. The substituents include different side chain carbohydrates and acids, including uronic acids, phenolic acids and acetyl groups. Xylans are underutilized industrially. There is thus considerable potential in obtaining xylans from industrial side streams and upgrade them to valuable products. Endoxylanases randomly hydrolyse the β-(1,4) glycosidic bonds of the xylose backbone of xylan producing xylooligosaccharides (XOS). The antioxidant activity (AA) of these XOS has been recently demonstrated. However, few knowledge exist about the effect of their decorations or their degree of polymerization on this property. In this work, the AA of XOS obtained from several substrates (beechwood and birchwood xylans, and arabinoxylan) was demonstrated. These XOS were obtained by three bacterial xylanases from different GH families, Xyn10A (family 10), Xyn11E (family 11) and Xyn30D (family 30). The XOS pattern depended on the xylanase used, being those produced by Xyn10A and Xyn11E neutral and acidic XOS whereas those produced by Xyn30D only acidic as demonstrated by TLC and MALDI-TOF MS. Interestingly, the fact that all the XOS obtained by Xyn30D contained the methylglucuronic acid ramification (acidic XOS) made substantially increase the antioxidant power of these sugars. Moreover, the nature of xylan also affected this property being those XOS obtained from birchwood and oat spelt of higher AA than beechwood XOS.  It was also demonstrated that as higher the molecular weight of XOS, greater was its AA. Finally, it was shown that ABTS was a more sensitive method for the AA determination of XOS than DPPH.

Distinct antioxidant activity of xylooligosaccharides obtained by several xylanases

2019 Spring National Meeting

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