an indirect competitive immunoassay for analysis of carminic acid in meat products

Carminic acid (ca), a member of natural dyes, is well known for its good stability in a variety of foods such as candies, drinks, and fruits. however, it has never been authorized as a food additive in meat products. in order to detect ca with high sensitivity and specificity, an indirect competitive enzyme-linked immunosorbent assay (ic-elisa) has been developed. a high-titer polyclonal antibody (pab) against ca was obtained after the immunization of new zealand white rabbits with conjugate of ca coupling with bsa. several physicochemical factors including ph value, ionic strength, and organic solvent were tested, and it was observed that the elisa working solution was ph 7.4 pbs buffer containing 50 mmol l−1 na+. under the optimal conditions, 50% inhibitive concentration (ic50) of ca was 95.2 ng ml−1 and the limit of detection (lod) was 1 ng ml−1. cross-reactivity of the pab toward carmine was 108.7%, and no response was found with other four edible colorants. the spiked meat samples were detected by ic-elisa with intra- and inter-assay recovery ranges of 79.1–103.1 and 81.6–98.8%, respectively. finally, the results for the fortified food samples were further confirmed by high-performance liquid chromatography (hplc) with a high correlation coefficient of 0.927, which demonstrated that the method in the study was sensitive enough for the quantification of ca in meat products.