Hardwood and softwood lignins from sulfite liquors: Structural characterization and valorization through depolymerization.

This work aims to evaluate the structural characteristics and study the oxidative depolymerization of lignins obtained from hardwood and softwood sulfite liquors. Lignins were obtained after ultrafiltration and freeze-drying of the sulfite liquors and characterized based on inorganic content, nitrobenzene oxidation, 13C NMR, and molecular weight determination. The structural characteristics achieved allow evaluating the potential of each lignin through oxidative depolymerization to produce added-value phenolic monomers. Hardwood and softwood lignins were submitted to alkaline oxidation with oxygen and the reaction conditions optimized to obtain a final oxidation mixture with the maximum yield of phenolic monomers. Through oxidation with O2, hardwood lignin generates mostly syringaldehyde while lignin from softwood biomass mainly produces vanillin; moreover, a lower reaction time and the interruption of O2 admission avoid the degradation of the oxidation products in the final mixture for both lignins, more evidenced to hardwood lignin due to its higher reactivity. From the results, it is possible to conclude that a phenolic aldehyde-rich oxidation mixture could be obtained, confirming the viability of lignin as raw material to produce added-value products as vanillin and syringaldehyde.

Enhancing trans-resveratrol topical delivery and photostability through entrapment in chitosan/gum Arabic Pickering emulsions.

The surfactant-free nature and higher stability of Pickering emulsions make them preferable solutions over conventional emulsions for skin applications. In this work, Pickering emulsions stabilized by chitosan/gum Arabic (CH/GA) nanoparticles were tested as vehicles for trans-resveratrol topical delivery. Skin absorption was examined ex vivo using Franz diffusion cells and porcine skin. Pickering emulsions allowed higher cutaneous retention and lower permeation of resveratrol, in comparison with a control solution based on a 20% v/v ethanol. The total amount of resveratrol retained in the skin, 24 h after the application, was 11.60% and 10.82% of the applied dose for the tested Pickering emulsion-based formulations prepared with 0.5% and 1.5% w/v CH/GA nanoparticles, respectively. In contrast, resveratrol skin retention from the control solution was only 2.86%. Confocal laser scanning microscopy revealed enhanced skin deposition of Nile Red to deeper layers from the Pickering emulsion-based formulations. Moreover, Pickering emulsions led to trans-resveratrol photostability increase, as measured after exposure to UV for 4 h. These results show that the CH/GA Pickering emulsions are promising solutions for the topical delivery of trans-resveratrol and have the potential to be used as green cosmetic products.