Preparation of Anti-Ractopamine Polyclonal Antibody and the Development of an Indirect Competitive Enzyme-Linked Immunosorbent Assay

Based on the polyclonal antibodies (pAbs), an indirect competitive ELISA (icELISA) has been developed for the determination of Ractopamine (Rac) residue in swine and cattle. Mixed anhydride method was employed to synthesize the artificial antigen of Rac-BSA and coating antigen of RacOVA; and two female New Zealand white rabbits were used to produce anti-Rac pAb. By the square matrix titration, the icELISA method was developed. The linear range was from 0.006 to 30 ng/mL, with LOD and IC50 value of 0.003 ng/mL and 0.44 ng/mL, respectively. Except for a moderate crossreactivity (34.5%) to Dobutamine, negligible cross-reactivity to the other compounds was observed. After optimization, 1:10 dilution in swine muscle and 1:20 dilution in cattle muscle produced the satisfactory B0 and IC50 values, respectively. When applied in real sample tests, the correlation coefficients (R2) of the concentration spiked and concentration determined were 0.9411 in swine and 0.9623 in cattle. Therefore, this assay has the potential for the rapid screening of Rac residue in food. Keywords-Ractopamine; Artificial antigen; Polyclonal antibody; Indirect competitive ELISA