Optimization of the formulation of chitosan edible coatings supplemented with carotenoproteins and their use for extending strawberries postharvest life

Abstract The aim of this study was to prepare chitosan (CS) edible films containing shrimp carotenoproteins (CP) and plasticized with glycerol and polyvinyl alcohol (PVA) using the casting method. The effects of CS (1–3%), glycerol (0–10%) and CP (0–3%) amounts on mechanical properties, antioxidant and antimicrobial activities of CS-CP composite films (CSCPFs) were studied using response surface methodology (RSM). The structural properties of CSCPFs were greatly influenced by CS, then by glycerol and CP amounts. According to the best fit and response surfaces, the optimized conditions were found to be 2.43% of CS, 9.93% of glycerol and 0.005% of CP. These conditions allow obtaining the highest elongation at break (149.11%) and tensile strength (24.07 MPa), as well as good antibacterial, antifungal and antioxidant activities of 20.64 mm, 21.93 mm and 51.08%, respectively. Due to their important antioxidant and antimicrobial properties, CS (1.5%) and CS-CP (1.5%–1%) edible coatings were used for strawberries preservation. Microbiological quality and physicochemical properties (pH, weight loss and titrable acidity) were evaluated during storage at 4 °C for 11 days. Results showed that CS and CS-CP coatings were effective on reducing the fungal decay (45–50%), as compared to the uncoated fruits (75%). In addition, it was observed that the weight loss of CS and CS-CP coated strawberries was significantly lower than that of the uncoated ones. Furthermore, phytopathogenic growth on the surface of cold-stored fruits was significantly inhibited for the coated fruits, which extend the strawberries shelf life during storage. Based on our findings, CS and CS-CP showed potential coatings for controlling food-borne bacteria and natural microorganism growth during the cold storage of strawberries.