Development of bacterial cellulose film coated with mixed colorimetric indicator for tracking the freshness/spoilage of ready‐to‐cook idli batter

The current study focuses on the fabrication of a mixed chemical colorimetric pH dye‐based indicator to monitor the freshness of ready‐to‐cook (RTC) idli batter stored under ambient conditions. The base of the indicator label was created using Acetobacter xylinum culture for the fabrication of a bacterial cellulose (BC) membrane film, and the characteristics of the developed film were analysed. Scanning electron microscopy identified the presence of a cellulose fibrils network and Fourier Transform–infrared spectroscopy indicated the presence of an amine group at wavenumber 1642 cm−1 on the developed BC film. Differential scanning calorimetry analysis identified the glass transition, onset, melting and end set melt temperatures as −30.3, 42.2, 85.6 and 105.9°C, respectively, and enthalpy as 209.2 Jg−1. The tensile strength of the developed base layer was found to be low at 27.11 ± 0.05 MPa. The developed base layer was coated with mixed colorimetric pH dyes of bromothymol blue and methyl red in a ratio of 2:3. The fabricated mixed colorimetric indicator label reacted as the carbon dioxide concentrations in the headspace increased from 0.15% ± 0.05% to 17.64% ± 0.11% (v/v) for up to 24 hours, and displayed a colour change of yellow for fresh to reddish orange for spoiled RTC idli batter stored under ambient conditions.