Pigment Characterization and Degradation Kinetics of Purple Corn Husk Extracts Under Sunlight and Dark Conditions

Natural pigments from plant-based sources are gaining attention as sustainable alternatives to synthetic colorants, yet their stability remains a major challenge. This study investigates the stability of pigments extracted from purple corn husk (Zea mays var. ceratina Kuleshov) using solvents of varying polarities, including ethanol, water, ethyl acetate, and n-hexane, under different light exposure durations. Pigment yields, phytochemical profiles, UV-Vis spectral data, and degradation kinetics were analyzed under transparent and dark storage conditions. Results showed that polar solvents yielded higher pigment quantities, with ethanol and water extracts rich in anthocyanins and flavonoids, while ethyl acetate and n-hexane extracts contained more stable compounds such as carotenoids and steroids. Under sunlight, ethanol extract exhibited the highest degradation at 33.93%, while ethyl acetate showed the best stability at 10.04%. Degradation followed first-order kinetics, with ethanol showing the highest degradation rate (k = 0.079 h⁻¹) and n-hexane the lowest (k = 0.020 h⁻¹). Dark storage significantly reduced degradation rates, with degradation after 5 hours of dark storage for ethanol at 13.76%, water at 6.54%, ethyl acetate at 6.89%, and n-hexane at 3.21%. These findings support the development of stable natural colorants for applications in functional foods, cosmetics, and nutraceuticals.