Abstract
Anthocyanins are natural dyes from plants that change color according to environmental changes, allowing for their potential use in real-time freshness-indicator films. In this study, black rice extract (BRE), black soya bean extract (BSBE), black wolfberry extract (BWE), purple sweet potato extract (PSPE), purple cabbage extract (PCE) and roselle extract (RE) were added to soybean isolate protein/chitosan (SPI/CS) films, and their performance was assessed. Results showed the total anthocyanin content of these six extracts were 1.50, 1.13, 1.98, 0.47, 0.33, 2.67 mg/mL, respectively. The presence of the six major anthocyanins was confirmed by mass spectrometry. Spectroscopy revealed that anthocyanin addition did not induce interactions between the extracts and SPI/CS film. Excess of anthocyanins weakened interactions between macromolecules, damaged membrane structure and reduced mechanical properties. Membrane water barrier properties improved with an increase in anthocyanin content, as well as antioxidant properties, but the difference between the indicator films was not significant. Finally, SPI/CS/RE exhibited a significant color change and the sensitivity was up to 50.6%, indicating the best application performance.
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