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 degrees 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.