Synergistic potential of thymol and red cabbage anthocyanin in biodegradable cellulose acetate labels for active and intelligent freshness monitoring of homemade tomato sauces

Colorimetric labels were developed using cellulose acetate (CA) as a base matrix in the presence of red cabbage anthocyanins (ANT) as a natural colorant and thymol (THY) as an active agent. CA/THY/ANT labels with different concentrations of ANT were prepared using the solvent evaporation method, to control food freshness and improve shelf life. The prepared labels were characterized by FTIR, SEM and other techniques. Anthocyanin-rich red cabbage extract confers to the labels a clear, stable and reversible color response in a pH range between 2 and 12, and average antioxidant properties. Thymol was added to the label as natural food preservative. The antibacterial properties against the pathogens tested were improved, without affecting the clear coloration of the labels and their response. To validate the use of these labels as an indicator of tomato sauce freshness, application tests were carried out on natural tomato sauces. The labels showed improved sensitivity to pH changes and a beneficial effect on the acidity and color of tomato sauce during storage. When tomato sauce deteriorates and loses its freshness, its pH becomes more basic, and its color darkens. The labels revealed a reduction in the bacterial load in the tomato sauce during storage at different temperatures, and as a result the tomato sauce maintains its pH and colour. The labels demonstrated also a possibility of reuse, by regeneration of the initial color. These results confirmed the possibility of using these new smart label to control freshness and extend the shelf life of foods.