Development of a novel on–off type carbon dioxide indicator based on interactions between sodium caseinate and pectin

Intelligent food packaging systems are a new concept and allow real-time monitoring of food conditions using indicators that are clearly visible to consumers. Among intelligent food packaging types, gas indicators detect changes in gas components in headspaces of food packages. This study aimed to develop a carbon dioxide (CO₂) indicator based on reactions of sodium caseinate (NaCas) and pectin. Transparency and pH were measured to confirm the changes in the appearance of the two polymers, and pectin concentrations were optimized for rates of change in transparency. In Fourier transform infrared spectroscopy and confocal laser scanning microscopy analyses, NaCas and pectin suspensions were characterized, and the associations between protein–polysaccharide interactions and pH changes were determined. Subsequently, the developed indicator was applied to kimchi packaging, and changes in pH, titratable acidity, lactic acid bacteria, and CO₂ contents of the kimchi packaging were determined and correlated with changes in transparency and pH of the indicator. The results demonstrated a strong correlation between parameters of kimchi and the indicator and warrant the use of visual CO₂ indicator in food packaging.