Impact of Anthocyanin Extract Sources on the Physical Properties and pH Sensitivity of Konjac Glucomannan/Zein Composite Film

The anthocyanin extracts (AE) from different sources were commonly used in preparing an indicator film to reflect food freshness, as AE contained rich anthocyanins which acted as the pH-sensitive ingredient. Therefore, this study aimed to compare the impact of AE sources (including rosella extract (RE), Lycium ruthenicum Murray (LE), and mulberry extracts (ME)) on the film properties and pH-sensitivity of konjac glucomannan/zein (KZ) composite film. Results showed that the three AEs had significantly different anthocyanin species and total contents, contributing to their different color changes in response to the pH changes. Some film property changes were not affected by the different AE, but mostly, different film property changing extents were observed, such as thickness, color, mechanical properties, hydrophilicity, antioxidant property, and water vapor permeability. This indicated that the hydrophilic plasticizing and void-filling effects of the anthocyanin were impacted by the anthocyanin structure. On the other hand, the impact of AE sources on the pH sensitivity and volatile ammonia sensitivity of the films was significantly different, mainly relating to both anthocyanin contents and composition. Finally, the KZ film with LE addition of 10% was suggested to be applied in the intelligent food packaging, as the addition of anthocyanin was relatively low and the film had both good pH sensitivity and film properties.