Chitosan/polyvinyl alcohol film containing beetroot peel and red cabbage extracts in freshness monitoring of trout fillet: gas or pH indicators

In this research, pH and gas sensitivity of the chitosan/polyvinyl alcohol film and coating containing beetroot peel (BRP) and red cabbage (RC) extracts were compared in freshness monitoring of rainbow trout fillet. The studied treatments were: Gas indicator film containing RC (G-RC) and BRP (G-BRP), pH indicator film containing RC (pH-RC) and BRP (pH-BRP), Gas indicator double-layer film containing RC (G-DRC) and BRP (G-DBRP), pH indicator coating containing RC (pH-CRC) and BRP (pH-CBRP), pH and gas indicator control film (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 fish fillets (7 Log CFU/g), (20 mg/100 g) and (score 3), respectively, which led to the color changes of the indicators. The designed indicators significantly (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 films containing RC and BRP extracts as pH indicators is a better method compared with gas indicators for spoilage monitoring of food. The highest correlation coefficient 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) significantly (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 film created the highest color spectrum by the pH changes of the stored fillets and can be considered as the most efficient film in the timely monitoring of trout spoilage and introduced in the commercial smart packaging.