Development of natural dye based biodegradable colourimetric intelligent packaging sensor labels

Abstract

Colourimetric indicators were prepared using anthocyanins, poly(vinyl alcohol) and cellulose nano-fibre by the electro-spinning technique. The indicator label containing 2000 ppm anthocyanin was found to be the optimal dye concentration. Fourier-transform infrared spectroscopy and X-ray diffraction results confirmed that the anthocyanin was incorporated into the poly(vinyl alcohol)-cellulose nano-fibre. The anthocyanin solution displayed pH dependent colour changes with solutions below pH 4 appearing rose red; at pH 5 and beyond it turns pink at pH 6 and eventually turns violet at pH 8. Blue-green was observed at pH 10. At highly alkaline pH 14 it turns yellow. Similar results were obtained when the anthocyanin containing indicator label was exposed to solutions of pH’s in the range 1 – 10 with the indicator label colour changing from red to green respectively. The indicator label was subjected to storage stability tests over 40 days by storing under nitrogen atmosphere, refrigeration conditions and at room temperature. The indicator label exhibited a high degree of colour stability with colour change (ΔE<4) under all conditions. The indicator label also showed significant colour changes from blue to violet to purple and ultimately pink when it was placed within the package of fresh cut green pepper for 7 days ambient conditions. These colour changes are a direct consequence of the increased carbon dioxide concentrations in the package resulting from deterioration of pepper at room temperature. Colour changes resulting from accumulating Total volatile basic nitrogen (TVBN) were also observed when the indicator label was placed in the headspace of packaged fresh chicken with the label changing from light pink to grey from day 1 to day 7 at room temperature storage. The results show that the label has great potential to be used as a visual in-package indicator of poultry products. Poultry and green peppers are food products with a potential for in-package quality detection by this indicator label. The results of the current work offer a new possibility to the applicability of water soluble, biodegradable indicators as real time quality detectors of bell pepper/chicken meat; it can be used alongside the best before date. Further work ought to be conducted to evaluate the effectiveness of this in-package freshness indicator label for fresh-cut pepper/chicken meat at different temperature conditions. Application of this freshness indicator for other fresh-cut fruit and vegetables also need to be further investigated

Keywords: Colourimetric indicators, anthocyanins, storage stability, TVBN, poultry, carbon dioxide, green pepper, in-package