Lignin micro/nanoparticles from alternative biomass sources for neutral-pH Pickering emulsions and quercetin encapsulation

Abstract

Conventional Pickering Emulsions (PEs) stabilizers are often petrochemical-based, raising concerns about bioincompatibility and adverse reactions. Using sustainable biomass, such as pruning residues, offers potential for natural PEs stabilizers development. This study explores the use of avocado pruning lignin (APL), alongside various commercial lignins, to produce natural stabilizers for neutral-pH PE. The effect of lignin chemical and structural composition to produce lignin nanoparticles (NP) and microparticles (MP) was studied. APL exhibited high carbohydrate content, contributing to excellent surface tension reduction and enhanced antimicrobial properties. However the presence of carbohydrates compromised APL solubility in acetone:water mixtures, hindering the nanoprecipitation process via the solvent exchange method. A washing step, consisting in the removal of water-soluble fraction of APL (APLWEF) improved this process. Both lignin NPs and MPs demonstrated effective stabilization of neutral-pH PEs, maintaining stability for up to 27 days with minimal changes in creaming index (CI). Quercetin encapsulation efficiency (EE) in all lignin types exceeded 90 %, except for APLWEF, which showed an EE around 78 %. The antioxidant activity in emulsions incorporating quercetin was particularly high, with kraft lignin sample maintaining an activity level of 0.93 mg of Trolox equivalents per g of emulsion at day 10, exhibiting minimal change from day 0.