Development of an Enzyme-Linked Immunosorbent Assay To Detect Benzylpenicilloic Acid, a Degradation Product of Penicillin G in Adulterated Milk

To avoid detection of penicillin G, some producers/merchants illegally add P-lactamase to milk to degrade it into benzylpenicilloic acid (BPA). This degradation product can cause allergic reactions in humans and, therefore, is a potential hazard to human health. To detect BPA in milk, we established a rapid direct competitive enzyme-linked immunosorbent assay (ELISA) with an IC50 of 0.32 +/- 0.01 mu g L-1, and a detection limit of 0.030 +/- 0.002 mu g L-1. Matrix effects in the milk samples were easily eliminated by centrifugation and dilution. Recoveries were 72.75-93.25%. Also heat treatments of raw milk did not affect the detection of the BPA. To validate BPA-ELISA, the spiked milk samples were analyzed by ELISA and LC-MS; the results showed a strong correlation (r(2) = 0.99). Incurred samples obtained from Tianjin Entry Exit Inspection and Quarantine Bureau (TJCIQ) were tested by BPA-ELISA. The results showed an almost 100% correlation (r(2) = 0.99) with the results supplied by the TJCIQ.