Extract of common mallow (Malva sylvestris) petals incorporated in starch/tragacanth gum film as a halochromic indicator for monitoring of Nile tilapia (Oreochromis niloticus) fillet quality

This study aimed to use common mallow (Malva sylvestris) extract (EMS) with ratios of 0.0, 0.5, 1.0, and 2.0% as an indicator in the film produced from corn starch/tragacanth gum matrix using a casting method to monitor the freshness of Nile tilapia fillets stored at 4 °C. The results showed that the total anthocyanin content of EMS was 1185.6 ± 0.58 mg cyanidin-3-glucoside Kg⁻¹. The starch/tragacanth gum films incorporated with 0.5 and 1.0% EMS were sensitive to the 0.8 and 1.4 M ammonia and their color changed after 20 min of exposure, while starch/tragacanth gum film incorporated with 2.0% EMS showed no visible color change in the presence of 0.2, 0.8 and 1.4% M ammonia. The Fourier transform infrared and X-ray diffraction spectra of the colorimetric films showed that EMS was successfully immobilized into the starch/tragacanth gum matrix. The moisture content and water solubility were significantly lower in the films containing EMS compared to those with no EMS supplementation. With increasing EMS concentration, water vapor permeability and ultimate tensile strength significantly decreased with the lowest values observed in films incorporated with 2.0% EMS (p < 0.05). The color of the starch/tragacanth gum films incorporated with 0.5 and 1.0% EMS was changed with a decrease in the quality and freshness of Nile tilapia fillet from pink to green and gray, respectively, after 12 days of storage at 4 °C. Findings of the present study illustrated that the pH-sensitive starch/tragacanth gum film incorporated with 0.5–1.0% EMS could be used as a halochromic indicator in the smart packaging of Nile tilapia fillet.