Kinetic Study of the Equilibration between Carminic Acid and Its Two Isomers Isolated from Cochineal Dye

Carminic acid (CA) is a major component of cochineal dye used in food additives, cosmetics, and pharmaceuticals. CA and its isomers, 2-C-α-glucofuranoside and 2-C-β-glucofuranoside of kermesic acid (DCIV and DCVII, respectively), were isolated from cochineal dye and the equilibrium constants (K) between CA, DCIV and DCVII were investigated. DCIV was partially converted to CA and DCVII, and DCVII was converted to CA and DCIV, whereas CA was very stable and only very slightly converted to DCIV and DCVII. Most of the DCIV and DCVII was converted to CA under aqueous conditions. The kinetic rate constants (k) for the degradation of DCIV within the first day of incubation at 24°C was determined to be 0.901 d^-1 and for the degradation of DCVII it was determined to be 1.102 d^-1. The k value for the formation of CA from the remaining DCIV was calculated to be 0.146 d^-1 and for the formation of CA from the produced DCVII it was found to be 0.148 d^-1. The K values were calculated as 1.22×10^-7, 2.61×10^-3 and 2.36×10^-3 mol/L for CA, DCIV and DCVII, respectively. These findings will be helpful for ensuring the safety and for aiding the quality assurance of cochineal dye products.