Freshness indicator for monitoring changes in quality of packaged kimchi during storage

A pH-sensitive dye-based freshness indicator system was prepared, and visible color changes based on the production of volatile acids and CO2 during kimchi storage were monitored. During fermentation, the pH of the kimchi, which was initially 5.4, decreased to moderate values of 4.2-4.4, and reached 4.0 at the end of fermentation. Based on pH and acidity, three fermentation stages were identified. Good correlation between the pH and acidity was observed. The highest CO2 concentration (60 %) and organic acid content (80 mg%) were observed during the optimum fermentation stage. Color changes of the freshness indicator accurately tracked an increase in CO2 concentration in the package headspace. The tested indicators all showed visible color changes with the fermentation stages of kimchi, and the values were significantly correlated with the CO2 concentration, pH, and acidity. Higher TCD values observed between the stages had a significant correlation with visible color changes. The storage, survey, and migration test results indicated that the dye did not migrate into the food materials and is safe for use inside the food package. Results of this study will be useful for developing a freshness indicator and determining the application of freshness indicator formulations and influencing consumer purchasing decisions.