Biodegradable Films Fabricated by Calcium Cross-Linking of Walnut Protein Isolate and Cellulose Nanofiber with Incorporation of Curcumin for Strawberry Packaging

There is an inadequate supply of environmentally friendly, versatile disposable packaging films for protecting various food items. Herein, a series of walnut protein isolate (WPI)-based bioactive films, including WPI (W) film, cellulose nanofiber (CNF)-reinforced (WN) film, Ca2+-cross-linked WN (WNG) film, and curcumin-loaded WNG (WNGJ) film, were successfully fabricated. WNG showed the best properties in terms of elongation at break (53.47% ± 4.94%) and hydrophobicity (water contact angle of 91.94° ± 1.71°). WNGJ film showed the best properties in terms of antioxidant and antibacterial activities. Compared to the group without film protection, exterior quality, weight loss, softening, pH decreasing, and solids loss of strawberries were delayed around 1–3 d by each package, indicating the improvement in freshness. All bioactive films were more effectively at reducing the juice loss (improved 16–50%) and the spoilage of strawberries than the commercial film at room temperature over 5 days. Among them, WNGJ showed the best properties in terms of maintaining the firmness, acidity, and total soluble solids of strawberries. The films with tunable hydrophobicity properties and bioactive functions possess considerable potential usage in maintaining the freshness of perishable fruit.