Preparation of a polyclonal antibody based heterologous indirect competitive ELISA for detecting ractopamine residue

Based on the polyclonal antibody (pAb), 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 immunogen while 1,4-butanediol diglycidyl ether was used to synthesize the coating antigen, thus producing the heterologous sensitivity; and two female New Zealand white rabbits were used to produce antiRac pAb. By the square matrix titration, an icELISA standard curve was established. The linear range was from 0.006 to 30 ng/mL, with LOD and IC 50 value of 0.003 and 0.44 ng/mL, respectively. Except for a moderate cross-reactivity (34.5%) to dobutamine, negligible cross-reactivity to other compounds tested was observed. After optimization, 1:10 dilution in swine muscle and 1:20 dilution in cattle muscle produced the satisfactory B 0 and IC 50 values, respectively. When applied in real sample tests, the correlation coefficients (R) 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.