Neutral fabrication of UV-blocking and antioxidation lignin-stabilized high internal phase emulsion encapsulates for high efficient antibacterium of natural curcumin

Abstract

By adjusting the polarity and conformation via the sulfomethylation modification, the bio-renewable enzymatic hydrolysis lignin (EHL) combined with alkyl polyglucoside (APG) was used as an emulsifier to stabilize the oil-in-water (O/W) high internal phase emulsions (HIPEs) for the first time under neutral conditions. The structure and sulfonation degree of the sulfomethylated lignin (EHL-XS) were characterized using gel permeation chromatography (GPC), Fourier transform infrared (FT-IR) spectroscopy, dynamic light scattering (DLS) and an automatic potentiometric titrator. The effects of the EHL-XS concentration, sulfonation degree and oil/water ratio on the microstructure and stability of HIPEs were investigated using an optical microscope and a rheometer. The results suggest that commercial lignosulfonates (LS) could not to stabilize HIPEs due to their high hydrophilicity. However, by using EHL-XS with sulfonation degree between 0.89 and 1.05 mmol g⁻¹, up to 2.0 wt% of EHL-XS with the assistance of 3.5 wt% APG could stabilize HIPEs containing 80 vol% of internal oil phase, which were super stable and displayed no significant microstructure changes over one month. Rheological investigation indicated that HIPEs with smaller droplet size and higher oil/water ratio exhibited higher surface elasticity and stability due to the tighter overall droplet packing. In addition, the EHL-XS stabilized O/W HIPEs could be used as encapsulates for the protection and delivery of the environmentally sensitive curcumin. It was found that such HIPEs encapsulation system exhibited superior UV protection of at least 30% higher than curcumin dispersed in bulk oil after 72 h of UV irradiation or 30 days at room temperature, respectively. Meanwhile, such HIPEs within curcumin also demonstrated good inhibitory activity against S. aureus.