Black goji anthocyanin-loaded emulsion film stabilized by rice protein hydrolysate complexes as pH-sensitive indicator for salmon freshness

Abstract

The present study aims to develop all-natural smart packaging films stabilized by complexes of rice protein hydrolysate, chitosan hydrochloride and black goji anthocyanin for effective monitoring of salmon freshness. The tertiary complexes were formed as driven by electrostatic and hydrogen bonding interactions upon facile pH variation, enabling the incorporation of soybean oil and the formation of emulsion films with considerable mechanical properties. Complexes formed at pH 5.0 in combination with 6 % soybean oil addition resulted in emulsion films with significantly lowered tensile strength from 12.1 to 3.9 MPa and improved extensibility of to 43.2 % from 23.1 % based on textural analysis, displaying high contact angle (>70°) to inhibit water vapor permeation. According to confocal laser scanning microscopy, the stabilization of emulsion film was predominated by trapping oil droplets within solid network formed by complexes, sterically hindering droplet coalescence and destabilization. Such emulsion film displayed high atmospheric pH sensitivity, allowing efficient response to production of volatile basic nitrogen substance (R²=0.97) during post-mortem storage of salmon fish. This study opens up the possibility of using edible ingredients in creating smart pH-indicating emulsion films, which allows to monitor food freshness and safety, enhancing quality control and providing consumer convenience in future food products.