Characterization and Application of Water Kefir-Derived Dextran as Coatings with Chitosan and Antagonistic Yeasts for Strawberry Preservation

Abstract This study developed alternative biobased coatings using dextrans extracted from household- and industrial-type water kefir grains (WKG) to extend the postharvest shelf life of perishable strawberries. Extracted dextrans were characterized for their structural, physicochemical, antioxidant, and antifungal properties, and the most promising exopolysaccharide was evaluated as a coating matrix alone or combined with chitosan and antagonistic yeasts under cold (4 °C) and ambient (25 °C) storage. Dextran extracted from household-type grain (D-WKS) exhibited significantly higher antioxidant activity across all three assays than dextran extracted from industrial-type grain (D-WKD) (57.40 vs 49.30% for DPPH, 60.70 vs 51.80% for ABTS, and 63.70 vs 56.60 μmol TE/L for FRAP). Furthermore, D-WKS displayed superior antifungal activity against eight postharvest mold pathogens, demonstrating larger inhibition zones (4.90–23.01 mm for D-WKS vs 1.43–13.54 mm for D-WKD) and lower minimum inhibitory concentration (MIC) values (0.1–100 mg/mL for D-WKS vs 1 to >100 mg/mL for D-WKD). Cold storage proved indispensable for quality preservation. Under cold storage, individual chitosan treatment was effective in limiting weight loss and maintaining fruit pH, °Brix, firmness, and chroma values. However, household-WKG dextran combined with chitosan (D-WKS+Cht) was the most effective in maintaining surface lightness (L), total phenolics, and redness (+a). Notably, after 10 days of storage at 4 °C, D-WKS alone most effectively suppressed disease severity (5.45%), infection ratio (9.09%), and enzymatic browning (ΔBI = 0.089) while achieving the highest sensory preference and consumer purchase intention. Overall, utilizing water kefir-derived dextran alone or in combination with chitosan under cold storage offers a promising and eco-friendly biocontrol strategy for strawberry preservation.