Preparation and characterization of antioxidant and pH-sensitive films based on chitosan and black soybean seed coat extract

Vegetable Additives in Food Packaging Polymeric Materials

“…Chitosan-plant extract films could effectively protect food against UV/visible radiation, for example, transmittance of chitosan-black soybean seed coat extract (BSSCE) was nearly in the 200-320 nm interval [205] and chitosan films containing aqueous hibiscus extract (HAE) exhibited transmittance below 10% in the 200-600 nm range [204], which was explained by the presence of several compounds in the plant extract, such as flavonoids, anthocyanin, phenolic acids, etc., which contains double bonds and could absorbs in UV/visible radiation [206].…”

“…For example, by changing pH from 7 to 3, different color variations (from brown to bright red) were observed in chitosan films containing black soybean seed coat extract (BSSCE) rich in various anthocyanins while the plain chitosan film was colorless and did not respond to pH changes [205]. Similarly, the color of purple-fleshed sweet potato extract (PSPE) encapsulated into the chitosan matrix could change the color with pH from pink-red (pH 3-6) to purple-brown (pH 7-8) to finally greenish-green (pH 9-10) (depending on the incorporated amount of PSPE) [220].…”

“…Anthocyanins, which are phenolic compounds with hydroxyl groups used as an indicator dye [221] could reduce the solubility of chitosan in distilled water [205] as they proved to support chitosan hydrogel formation with reduced water absorption and solubility [222]. Migration tests that showed that anthocyanins from chokeberry extract are both chemically bonded and physically immobilized in the chitosan matrix due to the interactions between the phenolic components and the hydroxyl and free amine groups of chitosan [209].…”

“…Phenolic components obtained from different kinds of plants can interact (intermolecular interactions) with hydroxyl and free amine groups of [264,265] that reduce the solubility of chitosan films: by hydrogen-bonding, electrostatic attraction (ionic complexations in acidic conditions) [266] between the anthocyanins and chitosan, and even through ester linkage [253,267]. For example, a small amount of purple-fleshed sweet potato extract (PSPE) (5 wt % on chitosan basis) could establish physical interactions with chitosan molecules and act as bridges among different chitosan chains [205,220].…”

“…The interactions of chitosan with phenolic substances through non-covalent bonds were proved by FTIR analysis, for example, for chitosan films containing black soybean seed coat extract (BSSCE) [205].…”