Starch-based biofilms incorporating lac (Laccifer lacca Kerr) as eco-friendly colorimetric indicators for headspace volatile spoilage gas detection

Lac-incorporated starch-based composite films were prepared and utilized as colorimetric indicator to monitor volatile spoilage gases released by shrimp. FTIR showed the newly formed ester linkages peak at approximately 1740 cm⁻¹ assigning to the C O stretching vibration of the neat plasticized -starch (ST) film. A broad amorphous peak of XRD of the ST film near 2θ = 21.0° indicated the disruption of the native semi-crystalline granular architecture into a disordered amorphous film network after glycerol-plasticized process. The incorporation of 1 (ST-L1) and 3 (ST-L3) wt% lac exhibited good dispersion, compatibility, UV-shielding, high water resistance (WCA > 75°), tensile strength (> 20 MPa) and optical clarity (>77% at 600–800 nm). The composite film showed a rapid pH-responsiveness to ammonia and changed its color from orange to orange-red (at pH 3.0–7.0) and from red-purple to purple (at pH 8.0–13.0). After exposure to volatile spoilage gases released by shrimp at 25°C, the transparency of the film decreased with increasing exposure time. The total color change ( ΔE* ) increased from 18.8 to 32.5 under exposure time from 12 to 24 h and could be readily distinguished by the human eye. Post-exposure, FTIR band shifts from 1576 to 1570 cm⁻¹ alongside increased broadening and intensity, which reflects the pH-induced structural transformation of the lac dye molecules. Furthermore, the ST-L1 film maintained high color response sensitivity ( S RGB > 37%, 12 h and S RGB > 57%, 24 h) without compromising its sensitivity to spoilage volatiles. These findings indicated the high potential of the prepared films as cost-effective, eco-friendly, and scalable biomaterials capable of serving as a non-contact colorimetric indicator for monitoring headspace volatile gases.