Screening of Naturally-Derived pH Dyes from Plant Extract Powders as Colorimetric Bio-Indicator and Possible Application in Intelligent Packaging Surachai Khankaew 1 , Waraporn Boonsupthip 2,3 , Chiravoot Pechyen 1,3 and Panuwat Suppakul 1,3,* 1 Department of Packaging and Materials Technology, Faculty of Agro Industry, Kasetsart University, Bangkok, Thailand 2 Department of Food Science and Technology, Faculty Agro-Industry, Kasetsart University, Bangkok, Thailand 3 Center for Advanced Studies in Agriculture and Food (CASAF), Kasetsart University, Bangkok, Thailand * E-mail: fagipas@ku.ac.th Abstract Consumer demand for mildly preserved, minimally processed, easily prepared and ready-to-eat “fresher” foods – together with the globalization of the food business, and the logistics of distribution from processing centers – pose major challenges for food quality and safety. A reduction in shelf life of foods as a result of microbial contamination and an increase in the risk of food-borne illness are driving forces for innovative means to monitor microbial growth in the foods while enhancing food safety. The use of naturally-derived pH dyes as colorimetric bio-indicator is of increasing interest due to the perceived lower risk of these to the consumer. However, there are few published data in the scientific literature that relate to bio-indicator for intelligent packaging application. As no single pH dye can cover the requirements for the communication of all foodstuffs, it is necessary to investigate a number of different candidates when developing this type of technology. Studies aimed at screening of naturally-derived pH dyes from plant extract powders including asian pigeonwings (Clitoria ternatea L.), hom (Strobilanthes cusia (Nee) Kuntze), indigo (Indigofera tinctoria L.), marigold (Tagetes erecta L.), red cabbage (Brassica oleracea var. rubra), roselle (Hibiscus sabdariffa L.), and turmeric (Curcuma longa) as colorimetric bio-indicator. This paper reported a preliminary study in which different concentrations of these naturally-derived pH dyes were tested their indicator sensitivity against the target metabolites. The light absorption spectra and the total color difference of those naturally-derived pH dyes solutions were also changed depending on pH values. Asian pigeonwings, marigold, red cabbage, and turmeric showed possible pH dyes for applying in intelligent packaging technology as a freshness bio-indicator. Keywords: Intelligent packaging; Naturally-derived pH dyes; Plant extract; Freshness bio-indicator