Water Resistance Improvement of Sodium Alginate and Black Wolfberry Anthocyanins Based Films Treated by CaCl2 for Food Packaging.

Abstract

The influence of calcium chloride (2% (w/v), 3% (w/v), 4% (w/v) or 5% (w/v)) as crosslinker on the performance of sodium alginate (SA) and anthocyanin extracted from black wolfberry (BWA) based films was observed. The results showed that after CaCl₂ treatment, the elongation at break reduced, but the water resistance, thermal stability, and tensile strength of SA/BWA films were significantly improved and they increased with the increase of CaCl₂ concentration. In which, 5%-CaCl₂ treatment endowed the films with optimal performance, which was specifically manifested by a decrease in the swelling ratio from complete dissolution to 163.4% within 60 minutes, water content from 24.9% to 13.1%, water vapor permeation (WVP) from 6.1 g·cm^-1·cm^-2·s^-1·Pa^-1·10^-12 to 1.6 g·cm^-1·cm^-2·s^-1· Pa^-1·10^-12, and an increase in water contact angle from 2.19° to 43.85°, tensile strength from 0.76 MPa to 13.15 MPa. Interestingly, CaCl₂ treatment slightly weakened the antioxidant activity (p < 0.05) but also had around 80% of DPPH radical scavenging rate and improved the visual color change of the film to pH. The films treated by 5%-CaCl₂ monitored the freshness of pork well. Therefore, comparing with traditional SA-based films, the CaCl₂ treated SA/BWA film is a better candidate for active and intelligent packaging application.