Zein-Induced Enhancement of the Thermal Stability of Anthocyanins Extracted from Agricultural Residues of Red Corn (Zea mays).

The stability of anthocyanins is a key factor limiting their use as functional natural colorants. This study evaluated the protective effect of zein on anthocyanins extracted from red corn (Zea mays) chaff, which is an underutilized agro-industrial byproduct. The extraction of anthocyanins was optimized using a Box-Behnken design, employing a 55.5% (v/v) aqueous ethanol solution at 45.21 °C and a solid-to-solvent ratio of 1.86 mg/mL (w/v). The resulting extract was rich in acylated anthocyanins derived from cyanidin, pelargonidin, and malvidin, which were identified using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FIA-ESI-FTICR-MS). The interaction between zein and the anthocyanins was found to be thermodynamically spontaneous (indicated by a negative ΔG), endothermic (ΔH = 19.8 kJ mol-1), and primarily driven by hydrophobic interactions (ΔS = 84.5 J mol-1 K-1). The addition of zein significantly decreased the degradation rate constant of the anthocyanins and increased their half-life, especially at pH 4 and storage temperatures of 4 °C and 20 °C. Moreover, the activation energy (Ea) for the zein-anthocyanin complex formation was lower (ranging from 63.64 to 47.75 kJ mol-1) than that of the extract without zein (ranging from 59.36 to 74.71 kJ mol-1), indicating that the zein complex has lower thermal sensitivity. Additionally, zein enhanced the red hues of the extract (increasing a* to 62.66) and preserved its antioxidant capacity, which even increased by up to 3.5 times under accelerated degradation conditions. Zein serves as an accessible and effective plant-based alternative for stabilizing anthocyanins in acidic environments, with potential applications in the development of functional natural colorants for the food industry.