Thermal degradation kinetics of aqueous anthocyanins and visual color of purple corn (Zea mays L.) cob

Purple corn cob was the byproduct during the corn processing. Thermal degradation kinetics and Hunter color parameters (a⁎, b⁎, C⁎, h° and ΔE) of aqueous anthocyanins from purple corn cob were studied at selected temperatures (70 °C, 80 °C and 90 °C) at pH 4.0. The results indicated that the thermal degradation of anthocyanin and Hunter color C⁎, a⁎ and ΔE parameters followed the first-order reaction kinetics, while Hunter color h° and b⁎ parameters followed zero-order reaction kinetics. The calculated values of activation energies (Ea) were 18.3, 35.9, 37.1, 31.6, 34.9 and 30.0 kJ/mol for anthocyanins, C⁎, a⁎, ΔE, h° and b⁎ parameters, respectively. The higher Ea indicated that greater temperature sensitivity of visual color as compared to anthocyanins content. The degradation of anthocyanins showed positive correlation with C⁎ (R2 > 0.909), a⁎ (R2 > 0.860) and ΔE (R2 > 0.940), while the degradation of anthocyanins showed negative correlation with h° (R2 > 0.828) and b⁎ (R2 > 0.735) during heating.Industrial relevancePurple corn cob was the byproduct during the corn processing. Purple corn cob is dark purple to almost black color due to its high content of anthocyanins, which makes this byproduct a good source of anthocyanins. In this study, the excellent linear correlation between Hunter color parameters (a⁎, b⁎, C⁎, h° and ΔE) and content of anthocyanins showed that the Hunter color parameters may also be used instead of anthocyanins content during heating. The advantage of using the visual Hunter color parameters may be measured as on-line quality control parameters during thermal processing of food industry.