Evaluation of the Biochemical, Colorimetric, and Microbiological Stability of Red Cabbage Anthocyanin Extracts for Application as Natural Indicators

Food spoilage is accompanied by changes in pH, which allows freshness to be monitored using colorimetric indicators. Due to their color response, the anthocyanins in red cabbage are of interest for smart packaging. However, their applicability depends on their stability during storage. This study evaluated the stability of red cabbage anthocyanin extracts obtained in water and in 50% ethanol, monitored for 10 days by analyzing total anthocyanin content (TAC), antioxidant activity (DPPH), colorimetric properties, color stability as a function of pH, degradation kinetics, and microbiological load. The ethanol extracts exhibited the best stability, with TAC decreasing from 116 to 73 mg CGE/100 g FW (t½ = 16–76 days), compared to the aqueous extracts, in which TAC decreased from 74 to 38 mg CGE/100 g FW (t½ = 9.5 days). DPPH followed the same trend, with a maximum half-life (t½) of 67.7 days. Temperature was the main factor contributing to degradation, followed by light and oxygen. Color varied depending on pH, ranging from red under acidic conditions to blue–green under alkaline conditions. The ethanolic extract exhibited the best color stability (ΔE < 1). Its stability at 4 °C, corresponding to food refrigeration conditions, highlights its potential as a colorimetric indicator.