In this research, pH and gas sensitivity of the chitosan/polyvinyl alcohol flm and coating containing beetroot peel (BRP) and red cabbage (RC) extracts were compared in freshness monitoring of rainbow trout fllet. The studied treatments were: Gas indicator flm containing RC (G-RC) and BRP (G-BRP), pH indicator flm containing RC (pH-RC) and BRP (pH-BRP), Gas indicator double-layer flm containing RC (G-DRC) and BRP (G-DBRP), pH indicator coating containing RC (pH-CRC) and BRP (pH-CBRP), pH and gas indicator control flm (pH-C and G-C) and coating (pH-CC) without extract. After 3 days of storage period, bacterial population, total volatile basic-nitrogen (TVB-N) value and sensory features of the studied samples exceeded the standard level for fsh fllets (7 Log CFU/g), (20 mg/100 g) and (score 3), respectively, which led to the color changes of the indicators. The designed indicators signifcantly (P ≤ 0.05) displayed higher sensitivity to the pH changes compared to the gas accumulation of the spoiling trout. Therefore, it seems that usage of smart flms containing RC and BRP extracts as pH indicators is a better method compared with gas indicators for spoilage monitoring of food. The highest correlation coefcient of color changes of the indicators to spoilage factors such as total viable count (R2 = 0.84), psychrotrophic bacteria (R2 = 0.89), pH (R2 = 0.70), TVB-N (R2 = 0.75) values, odor (R2 = 0.93), color (R2 = 0.94), and overall acceptability (R2 = 0.94) signifcantly (P ≤ 0.05) belonged to the pH-RC group, and G-RC, pH-BRP, G-DRC, pH-CRC, G-BRP, G-DBRP, and pH-CBRP groups were in the next ranks, respectively. It can be concluded that pH-RC flm created the highest color spectrum by the pH changes of the stored fllets and can be considered as the most efcient flm in the timely monitoring of trout spoilage and introduced in the commercial smart packaging.
