Natamycin-Loaded Soy Protein Isolate/Cellulose Nanofibril Edible Composite Film for Improving the Postharvest Quality of Blueberries

This study aimed to prepare a free-standing composite film consisting of soy protein isolate (SPI), cellulose nanofibers (3.0% CNF) and natamycin (3.0% NA) to maintain the freshness of postharvest blueberries, which are prone to spoilage and deterioration as a result of fungal infections. The antifungal performance of SPI–CNF–NA composite films against Aspergillus niger was determined via plate-based assay; its inhibition zone diameter against A. niger CICC 40868 reached 35.22 mm. Adding optimal amounts of CNF and NA maintained the SPI–CNF–NA composite film’s desirable buffer performance against water vapor, oxygen and ultraviolet light. In the blueberry preservation experiment, compared to the control group, SPI–CNF–NA composite film treatment reduced the weight loss rate of blueberries by 28.30%, and increased the contents of soluble solids, titratable acid and anthocyanins by 10.78%, 14.20%, and 33.13%, respectively. Applying the fabricated SPI–CNF–NA composite film not only maintained the freshness and exterior quality of postharvest blueberries, but also favored the preservation of their internal nutrients during a 20-day storage period. In summary, the addition of CNF and NA to prepare the SPI–CNF–NA composite film shows potential to improve the quality of postharvest blueberries. This study provides a theoretical and technical basis for the development of high-performance, stable biopolymer composite materials.