Novel bio-based, time-temperature dependent colorimetric ink and film containing colorants from the red pitaya (Hylocereus costaricensis)

Natural colorimetric indicators are environmentally friendly and safe alternatives to those based on synthetic materials. However, low stability limits the use of many natural colorants in commercial settings, especially at high temperatures. This study demonstrates the application of betalains extracted from the peel of red pitaya (Hylocereus costaricensis) as natural colorants in diagnostic packaging materials. Extracted betalain pigment (BP) and dye (BD) were applied to BP-based screen-printing ink (BPi) and BD-based film (BDf), respectively. The color transitions of BPi and BDf were observed at high temperatures as a function of time. BPi could be screen printed with good appearance properties. BD could be applied homogeneously to a methylcellulose thin film. Both BPi and BDf exhibited a color change from the initial pink to orange and yellow, respectively, depending on tem-perature and storage time. At 180 degrees C, a complete change in color was observed for both BPi (7.5 wt% BP) and BDf (7.0 pphr of BD) with Delta E of 22.03 (50 min) and 23.95 (6 min), respectively. The activation energy (Ea) of BPi and BDf were 25.8474 and 63.6420 kJ mol(-1), respectively. Therefore, BPi and BDf are promising bio-based materials for the development of time-temperature dependent materials.