Immunochemical detection of fraudulent adulteration of pork chorizo (sausage) with soy protein

Rabbit polyclonal antisera were produced against soy flour proteins extracted with 0.5 M NaCl solution and purified by affinity chromatography to detect adulteration in pork chorizo (sausage) with an enzyme-linked immunoabsorbent assay (ELISA). To detect adulteration the following saline extracts were prepared: 100% pork and 100% soy chorizo and mixtures of these two products (90:10, 80:20, 70:30, 60:40, 50:50, 40:60, 30:70, 20:80, 10:90), and extracts of two commercial chorizos labeled as pork. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed that the salt solution was the most suitable for protein extraction compared to water and a 1% SDS solution. The commercial chorizos did not have the characteristic electrophoretic pattern for pork chorizos. The antibodies were specific for soy and its products, as there was no response to other vegetable and animal proteins by gel immunodiffusion assay or ELISA. The standard curve obtained with the ELISA results of the chorizo mixtures gave a correlation coefficient of r(2) = 0.988. The two commercial chorizo values resulted in a 32 and 40% soy substitution. Total time for ELISA was optimized to 4 h, and 2 h if the plates were previously activated with the antigen. Variation coefficients of ELISA readings for replicates of the same extract in one plate and variation of different assays on different days were 2.3 and 8% respectively.