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\subsection{Film preparation}  Colourimetric TTIs are based on chemical, physical and enzymatic processes\cite{Arias_Mendez_2014} and have wide application in smart packaging, with applications to chilled or frozen foods. In smart packaging, this kind of sensors change their colour due to a change in a critical state, for example, the growth of micro-organisms fires changes in pH of the food, which in turn induces a colour change in a indicator dye, allowing the packaging to provide visual information about the product.\par  Thus, these These  films are basically prepared by the casting technique. technique, which has low cost and high efficency for film preparation.  There are several pigments used for the purpose of sensors and very research in the development of these sensors in alternative thin films on packaging from oil. Among the most diverse natural products that have been studied, biopolymers such as starches, gums, pectin, gelatin and chitosan are the ones that have stability, because they form networks structured copolymers. In addition to biopolymers, various natural pigments are also being investigated with regard to application in sensors in thin films.