Aqueous Esterification of Cellulose with Amino Acids Enables Biomass-Based Pickering Emulsion Coatings for Fruit Preservation

Postharvest fruit losses remain a persistent challenge for sustainable food systems, while many coating technologies still rely on synthetic additives or solvent-intensive processes. Here, we report a fully sustainable route to interfacial cellulose stabilizers for edible Pickering emulsion (PE) coatings. Cellulose was modified via aqueous ball-milling-assisted esterification using valine, isoleucine, and phenylalanine as modifiers, yielding three nanocellulose families with tunable substitution degree and enhanced hydrophobicity. Among these samples, valine-modified cellulose exhibited the highest degree of substitution and the strongest hydrophobicity, which is attributed to its superior water solubility and esterification efficiency. The optimized formulation reached a water contact angle of 82.4° and formed stable soybean-oil emulsions with a mean droplet size of 14.47 μm. To integrate bioactivity, quercetin was directly dissolved in the oil phase to produce antioxidant-functionalized PEs with high encapsulation efficiency (up to 88.56%). Under synergistic antioxidant and moisture-retention effects, the coating reduced mass loss by 49.7% in fresh-cut apples and 60.5% in strawberries, accompanied by significantly delayed browning and maintained sensory acceptability and edibility. Overall, this study establishes an all-biomass preservation platform that links aqueous cellulose esterification to interfacial engineering, antioxidant delivery, and practical postharvest protection, offering a scalable strategy for next-generation food-contact coatings.