Enzymatic and chemical oxidation of polygalactomannans from the seeds of a few species of leguminous plants and characterization of the oxidized products

An aerogel obtained from chemo-enzymatically oxidized fenugreek galactomannans as a versatile delivery system

“…1.10.3.2, see Riva, 2006;Rodgers et al, 2010;Witayakran & Ragauskas, 2009), in combination with the mediator TEMPO for laccase regeneration (Bragd, van Bekkum, & Besemer, 2004), oxidizes primary hydroxyl groups of GM in an unbuffered aqueous solution of guar galactomannan, causing a substantial viscosity increase of the polysaccharide solution, which is converted to an elastic gel, as confirmed by its modified rheological profile. In a follow-up publication (Merlini et al, 2015), we reported that the laccase/TEMPO oxidation system yields elastic gels also in the case of four other leguminous gum solutions (i.e., locust bean, tara, sesbania and fenugreek) and have also shown that the higher the galactose content of the GM, the higher the viscosity increase. Indeed, fenugreek gum (FG) oxidation gave the most dramatic results under the experimental conditions used, with a surge in viscosity of over fifteen-fold, to generate a very compact, elastic hydrogel, that, even after partial depolymerization with a ␤-mannanase, was able to preserve some of its "gel-like" structure.…”

“…Laccase, TEMPO-mediated, oxidation of FG was carried out following the procedure previously described by Merlini et al (2015). Purified FG was dissolved under constant mechanical stirring in 100 ml of MilliQ water (1.075%, w/w) at room temperature for 30 min in order to develop a final viscosity around 1800 mPa s and the solution was kept still overnight at room temperature.…”

“…In the first step, primary hydroxyl groups of FG galactose residues are chemo-oxidized to carbonyls by the laccase/TEMPO catalytic system (Lavazza et al, 2011;Merlini et al, 2015). In the reaction, TEMPO is firstly oxidized to an oxoammonium ion, which in turn selectively oxidizes primary OH's to the corresponding aldehydes (see also : Ding et al, 2008;Marzorati, Danieli, Haltrich, & Riva, 2005;.…”

“…The storage polysaccharide found in its seed endosperm is a galactomannan, similar to locust bean, guar and tara gum, but more extensively branched (Wei et al, 2015). The Gal: Man ratio in fenugreek GM was estimated to be close to unity by HPLC analysis (Brummer, Cui, & Wang, 2003) and confirmed by NMR (Merlini et al, 2015).…”

“…The average ratio of galactose to mannose (Gal: Man) is variable, depending on the plant source, and ranges from 1: 4.5 in cassia (Cassia tora) to 1: 1 in fenugreek (Trigonella foenum-graecum) http://dx.doi.org/10.1016/j.carbpol.2016.02.007 0144-8617/© 2016 Elsevier Ltd. All rights reserved. (Crescenzi et al, 2004;Daas, Schols, & de Jongh, 2000;Daas, Grolle, van Vliet, Schols, & de Jongh, 2002;Daniel, Whistler, Voragen, & Pilnik, 1994;Liyanage, Abidia, Auldb, & Moussa, 2015;McCleary, Clark, Dea, & Rees, 1985;Merlini, Boccia, Mendichi, & Galante, 2015;Sittikijyothin, Torres, & Gonç alves, 2005;Wei et al, 2015). This peculiar structure makes them fairly soluble in water at different temperatures, flexible in application and chemically/biochemically quite reactive (Cheng, Prud'homme, Chick, & Rau, 2002).…”