Intelligent pH-responsive colorimetric films based on κ-carrageenan/grape peel extract for real time monitoring of food freshness

The need for innovative packaging solutions have fuelled the research in indicator films from natural sources. In this study, an intelligent pH-responsive colorimetric film has been developed based on κ-carrageenan, Myristica fragrans extract (MFE) and grape peel extract (GPE). The κ-carrageenan act as a biopolymer matrix, GPE, composed of anthocyanin rich compounds act as the main pH indicator and MFE imparts color stability which helps to maintain the anthocyanin compounds present GPE in flavylium cation form, enabling swift response to pH change induced by volatile amine groups released from the spoiled food. The indicator films showed excellent UV protection and water barrier properties. The incorporation of MFE aided in enhancement of mechanical properties and hydrophobicity of indicator films enabling its storage at 25°C and 4°C. The film exhibited distinguishable color changes from pale red to red or violet and to blue or green, clearly indicating the distinct phases of food condition. The indicator film showed visual color changes for packaged shrimp, tuna, mushroom and milk stored at 25°C and 4°C. The TVB-N values, microbial load, MDA content and pH of packaged samples were in accordance with the color change of indicator films giving conclusive information on the status of food real time.