Postharvest preservation of apples and potatoes using a Dictyosphaerium algal oil emulsion–chitosan hydrogel coating: efficacy against Enterobacter mori.

Microbial spoilage after harvest is a major cause of loss of perishable crops, and therefore preservation methods that are cost-effective and efficient are required, especially in resources limited situations. Here, algal oil extracted from Dictyosphaerium sp. (DHSYM) was formulated as an oil-in-water emulsion and incorporated into a chitosan hydrogel coating to inhibit Enterobacter mori and extend the shelf life of apples and potatoes. The resultant emulsion showed a Z-average droplet size of 831.3 nm and a polydispersity index value (PDI) of 0.341 and thus had a relatively small droplet size distribution. In agar diffusion assays, the emulsion produced inhibition zones of 9-17 mm (5-15 mg/mL), while emulsion-loaded chitosan hydrogel increased inhibition to 11-19 mm compared with hydrogel alone (~7 mm) [control: cefotaxime 20 mm]. The coating exhibited a hydrophilic property reaching 39 o contact angle and cell viability of 80-85% in HEK-293 cells across tested concentrations, suggesting low cytotoxicity. When applied as a dip-coating, the hydrogel increased apple shelf life by ~1 week and preserved potatoes for >1 month under the tested storage conditions. Structural and functional characterizations were conducted to assess the properties of the hydrogel, including SEM, FTIR, RAMAN, GC-MS, compression analysis, thermal gravimetric analysis, contact angle measurement, biofilm eradication, antibacterial activity, MTT assay, molecular docking, and toxicity profiling. GC-MS detected several compounds; selected ligands (D-limonene, oxalic acid diallyl ester, piperazine, 1,3 bis dimethylethyl and carbonic acid) were prioritized for docking based on reported antimicrobial relevance. These findings prove algal emulsion-chitosan hydrogels as a promising bio-based coating; however, validation with larger sample sizes, defined storage conditions, and statistical comparisons are required.