On hexenuronic acid (HexA) removal and mediator coupling to pulp fiber in the laccase/mediator treatment

Improvement of TCF Bleaching of Olive Tree Pruning Residue Pulp by Addition of a Laccase and/or Xylanase Pre-Treatment

“…Figure 6a shows how the a* coordinate shifted to the right (from green to red) and the b* coordinate increased (from blue to yellow) in all bleached pulps after accelerated ageing. Similar results have been reported with different raw materials (Cadena et al 2011;Eugenio et al 2011;Martin-Sampedro et al 2012). Figure 6b shows an increase in color (C*) and a reduction in lightness (L*) in all pulps, after accelerated ageing, which is consistent with previous reports (Eugenio et al 2011;Martin-Sampedro et al 2012).…”

“…This increase in the kappa number could be associated with grafting of the natural mediator (acetosyringone) to the fibers. It has been suggested that mediators can remain temporarily stuck to the fibers, consuming reagent during the kappa number determination (Dyer and Ragauskas 2004;Cadena et al 2011;Fillat et al 2012).…”

Assessing the use of xylanase and laccases in biobleaching stages of a TCF sequence for flax pulp

“…This must have resulted from direct oxidative elimination of readily accessed HexA molecules on the outer parts of fibres. 20 However, the mediators altered the HexA removal efficiency: whereas SA had no effect on the HexA reduction caused by laccase from P. cinnabarinus, VA enhanced the effect of PcL, probably because the oxidized form of the mediator was able to penetrate deeper into fibre walls and attack HexA molecules there.…”

“…16 -19 One highly innovative use of xylanases and laccases is for reducing the hexenuronic acid (HexA) content of pulp, whether by releasing xylans (xylanases), direct oxidation (laccases) or via an as yet unknown mechanism. 20 Hexenuronic acids, which form during alkaline cooking of pulp, have adverse effects on pulp bleaching; thus, they contribute to kappa number, cause brightness reversion and oxalic acid formation, consume bleaching agents and retain metal ions by chelation. 21,22 In this work, we assessed the use of various enzyme delignification stages in an industrial bleaching sequence.…”

Development of novel antibacterial active, HaCaT biocompatible and biodegradable CA-g-P(3HB)-EC biocomposites with caffeic acid as a functional entity

“…Most phenols like caffeic acid, as natural auxiliaries host antimicrobial activity and can also be grafted to improve or impart existing or antimicrobial properties, respectively. The cross-linking of some of the natural phenolic compounds to different polymers is evidenced after an enzymatic stage with P. cinnabarinus laccase [9,10]. Laccase catalyses the oxidation of aromatic compounds using molecular oxygen as electron acceptor thus has been successfully applied for grafting of phenolic compounds on different natural polymers.…”