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\section{Colorimetric TTI (Time-Temperature Indicators) Films for Food Packaging Systems}  Time-temperature indicator (TTI) films are among the most promising intelligent packaging systems for the food industry. TTI films can safely indicate for the manufacturer or the final consumer, in real-time, the conditions of food processing, transportation, storage and deterioration. Nevertheless, it has the advantage of being of low cost and visually indicate the food conditions. The main idea behind TTIs is that many food products deteriorate due to changes in the temperature, which cause chemical reactions and microbial growth that can be detected by a TTI film. Several types of TTI, such as colorimetric~\cite{Pacquit2006, Pacquit2007, Wu2013, Yoshida2014, PereiraJr2014a, Zhang2014}, radiofrequency~\cite{Length2010}, photochromic~\cite{Kreyenschmidt2010}, bacterial growth kinetic~\cite{Zhang2013}, intelligent inks~\cite{Mills2005}, oxygen indicators~\cite{Vu2013, Eaton2002}, as well as nanotechnology sensor systems have been developed and successfully tested both in academy and in the industry. Among these systems, colorimetric TTI systems which can provide a response \textit{via} a color change according to pH changes of the product, providing information about the conservation and the actual quality of a food in a visual and intuitive way, have grown in importance and diversity, both in industry and academy, mainly due their low cost, simplicity and reliability. Besides their simplicity, the common feature of such systems is that they are based on biodegradable polymeric films and pH indicator dyes, thus not requiring expensive analytical instruments. Furthermore, there is a great interest of the food industry, retailers and consumers for environment friendly systems that can safely be applied as an accurate intelligent food-package.\par  As colorimetric TTIs based on carbohydrate polymers as a supporting matrix with indicator dyes have been developed~\cite{Zhang2014,Nopwinyuwong2010,PereiraJr2014a,Golasz2013,Yoshida2014,Kuswandi2012} developed~\cite{Zhang2014,Nopwinyuwong2010,Pereira_2015,Golasz_2013,Yoshida_2014,Kuswandi_2012}  and well-stablished in the literature, this chapter section will report the techniques of preparation and characterization of such systems as well as the perspectives of future development and real applications. \par  \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  These films are basically prepared by the casting technique, which has low cost and high efficency for film preparation. Briefly, composite hydrocolloid films are prepared by suspending an amount of biopolymer in distilled or deionized water. The suspension is poured in acrylic or glass plates and dried until constant weight in order to obtain the films. The casting of hydrocolloid suspension films has been successfully applied in the development of smart films prepared with polyaniline\cite{GARCIA_2004}, Cassava Starch/Glycerol\cite{Golasz_2013}\cite{Kuswandi_2012}, Chitosan\cite{Yoshida_2014} ,Chitosan/PVA\cite{Silva_Pereira_2015}\cite{Pereira_2015},  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.