pH and thermal stability of black carrot (Daucus carota ssp. sativus var. atrorubens Alef.) anthocyanins: the impact of copigmentation

Abstract

This study aimed to investigate the thermal and pH stability of anthocyanins in black carrot extracts (BCEs) when exposed to a temperature of 90 C-degrees for 6 h. This investigation was conducted with BCEs both in pure form and in the presence of copigments such as mandarin peel extract (MPE), pomegranate peel extract (PPE), and rose petal extract (RPE) in model solutions with varying pH (2.2, 2.8, 3.2, 3.6, 4.2, 4.8, and 5.4). The stability of black carrot anthocyanin (BCA) was assessed based on its ability to withstand the elevated heating temperature and maintain its color intensity under various pH conditions. The results indicated that copigmentation enhanced the pH, color, and thermal stability (to a certain extent) of BCEs. The pH stability was found to be higher in the samples copigmented with MPEs and RPEs. These results suggest that the decline in the monomeric anthocyanin content and higher color density might be due to polymerization and/or copigmentation rather than degradation. The maximum polymeric color was observed in the MPE-copigmented sample (58.05%), followed by the samples copigmented with RPE (52.94%) and PPE (24.61%) at pH 5.4. Moreover, we found that the thermal degradation of black carrot anthocyanins is a unimolecular serial-type reaction involving reactive intermediates. The proposed degradation pathway suggests that the first stages of degradation include the removal of sugar molecules and glycosidic bonds.