Enzyme-catalyzed transesterification of galactomannan extracted from mesquite seed (Prosopis velutina) with vinyl carboxylate esters

Abstract

Galactomannans (GM) are hemicellulosic polysaccharides composed of D-mannopyranose chains linked by β (1 → 4) glycosidic linkages with branches of D-galactopyranose linked by α (1 → 6) linkages. This polysaccharide is recognized for its hydrophilic character, as it is rich in hydroxyl groups (-OH). This chemical characteristic, combined with the absence of ionic charges, enables structural modifications such as transesterification of the fatty acid chains (FA), which provides a strategy for obtaining amphiphilic structures. The enzyme-catalyzed syntheses were carried out in DMSO with GM decanoate (GMD) and GM palmitate (GMP) at different molar ratios (0.5 and 1.0) and the resulting structures were evaluated with infrared spectroscopy (FTIR), solid-state nuclear magnetic resonance (CP/MAS 13C NMR) and differential scanning calorimetry (DSC). The FTIR spectrum confirmed the transesterification of GM with the appearance of a CO band (1730-1750 cm−1). These results were confirmed by the signals observed at 177 and 30 ppm in the CP/MAS 13C NMR spectrum, which corresponded to the CO groups of the esters and the terminal –CH3 groups of the FA chains, respectively. Finally, DSC showed glass transition temperatures (Tg) in the range 43–51 °C, while the melting temperatures (Tm) of the GM esters (59 °C) were not affected by different degrees of esterification (DE) for GMD (0.37 and 0.71) and GMP (0.47 and 0.57).

Keywords

• Galactomannan ester
• Enzymatic catalysis
• Amphiphilic polysaccharides
• Transesterification