Stabilization of grape skin anthocyanins by copigmentation with enzymatically modified isoquercitrin (EMIQ) as a copigment

The thermal and light stability of grape skin anthocyanins with enzymatically modified isoquercitrin (EMIQ) as a copigment was investigated at different pH levels of 3, 4 and 5. The ratios of anthocyanins to EMIQ were 2:1, 1:1, and 1:2 (w/w), respectively, in the thermal experiments at 90 °C, and EMIQ concentrations (0.25, 0.5, and 1%, w/w) were evaluated respectively in the light experiments. Results revealed that the degradation of anthocyanins copigmented with EMIQ followed first-order reaction kinetics. The half life of anthocyanins extended significantly with the increase of EMIQ concentration (p < 0.05), moreover, the color stability increased due to the addition of EMIQ as the total color difference values ΔE* were smaller for the copigmented anthocyanins. The magnitude of the bathochromic (λmax) shifted to the longest wavelength absorption band with the increasing copigment concentration for all pH levels. Results demonstrated that EMIQ was an effective copigment to stabilize grape skin anthocyanins.