Comparison between anthocyanins from roselle and mulberry as pH indicators in development of intelligent films

Smart films incorporated with anthocyanins as color indicators to monitor the food spoilage has attracted great attention. However, the effectiveness comparison among anthocyanin sources remains limited. Hence in this study, chitosan-based films incorporated with varying concentrations of anthocyanins sourced from either roselle or mulberry were developed. Detailed structural, morphological, physical, mechanical, and functional characteristics of these films were evaluated and compared. In general, the composite films, incorporating anthocyanins from roselle or mulberry, exhibited a deeper red-purple hue and a rougher cross-sectional appearance than the one without anthocyanins. Furthermore, while all composite films shared some representative absorption bands of FTIR spectra, there were slight variations in their area and height due to the interaction between anthocyanins and film components. Incorporating anthocyanins into chitosan-based films did not significantly affect film thickness, ranging from 74.90 to 88.35 mu m. However, it notably reduced light transmittance and water vapor permeability (from 9.46 to 4.69-7.88 x 10-11 gm-1 s-1 Pa-1) while enhancing tensile strength (from 4.68 to 5.66-11.78 MPa), elongation (from 12.4 to 19.63-23.60%) and antioxidant activity (from 126.4 to 315.63-1044.54 mu g Trolox equivalent/g film). Additionally, the color change patterns of chitosan-based films embedded with anthocyanins from roselle or mulberry aligned with the pH values, transitioning from red to reddish-pink (pH 3-4), pink (pH 5-6), purple (pH 7-10), and green-yellow (pH 12). During the exposure to ammonia vapor, a dark red-purple was initially observed in composite films, then faded over time, and finally shifted into light yellowish color after one hour. Both anthocyanin sources exhibited quick sensitivity to ammonia and fish spoilage. However, the color change with MARE might be more noticeable. As a result, the composite films containing anthocyanins from roselle or mulberry could be employed as intelligent films for real-time food freshness indication.