ε-poly-l-lysine-grafted nanocellulose prepared by enzymatic oxidation for high-internal-phase Pickering emulsions and nutraceutical delivery.

This study presents a strategy for preparing ε-poly-l-lysine-grafted nanocellulose via TEMPO-laccase/O2 oxidation followed by aldehyde-directed Schiff-base coupling. The resulting nanofibrils, with lengths of 0.8-1.2 μm, exhibited zwitterionic behavior, with ζ-potentials ranging from +49 to -28 mV, while Schiff-base grafting at pH 9 afforded the highest surface amino-group density of 0.915 ± 0.08 mmol g-1. Owing to the combination of high-aspect-ratio fibrillar morphology and amphoteric surface functionality, ε-PL-TLOCN enabled the formation of ultra-stable oil-in-water high-internal-phase emulsions (HIPEs) with oil volume fractions up to 82% at nanofibril concentrations below 0.8 wt%, in contrast to conventional aminated nanocellulose systems that require much higher particle loadings. Using curcumin as a model lipophilic nutraceutical, the resulting HIPEs exhibited enhanced photostability and increased in vitro gastrointestinal bioaccessibility to approximately 60%, compared with about 30% for bulk oil. These results demonstrate that enzymatic oxidation combined with Schiff-base grafting provides an effective route for constructing multifunctional nanocellulose and highlight ε-PL-TLOCN as a promising stabilizer for high-internal-phase emulsions and oral delivery systems.