Utilisation of black sticky rice (Oryza sativa L.) extract in chitosan-methylcellulose film

Botanical extracts have potential for application in active food packaging systems in terms of antioxidant and antimicrobial activities, including other smart functions. In the present work, black sticky rice (Oryza sativa L.) extract (BE; 10 - 30%) was incorporated into a composite film of chitosan (1.0%) and methylcellulose (0.5, 1.0, and 1.5%), and prepared by a casting technique using polyethylene glycol (PEG 400) as a plasticiser. Application of 1.5% methylcellulose in combination with chitosan slightly increased film solubility and the water vapour permeability coefficient (WVPC), and improved physical properties as compared to other treatments. Film with a high BE content (20 - 30%) was thicker, and had a decreased WVPC. The tensile strength of the film increased in contrast to a statistically significant decrease (p ≤ 0.05) in the percentage of elongation at break. The surface morphology of the film was flat and smooth, and the cross section was more rigid when viewed under a scanning electron microscope. The colour of the film containing 30% BE changed clearly from red (pH 1.0) to pinkish brown (pH 6.0) and finally yellow (pH 12.0), indicated by decreased a* value and increased b* value. ΔE presented the total colour difference that changed from an initial before immersing. The film was responsive when tested in food systems by mounting it on the lid of the box, showing a visible orangebrown colour in torpedo scad, greyish brown in chicken tenderloin, and light orange in minimally processed pineapple when foods spoiled. The present work revealed the potential of anthocyanin extract derived from purple sticky rice for use as a natural pH indicator in chitosan-methylcellulose-based films for intelligent packaging