Development and evaluation of an immunomagnetic separation–ELISA for the detection of Alicyclobacillus spp. in apple juice

The immunomagnetic separation (IMS) technique was used in combination with an enzyme-linked immunosorbent assay (ELISA) procedure to shorten the total analysis time and improve the sensitivity for the detection of Alicyclobacillus spp. in apple juice samples. The specificity of IMS–ELISA for twenty strains of Alicyclobacillus spp. and eighteen strains of non-Alicyclobacillus spp. was determined and there was little cross-reaction with non-Alicyclobacillus strains. Artificially contaminated apple juice with different concentrations of Alicyclobacillus acidoterrestris was detected by IMS–ELISA, and the detection limit of the assay in apple juice was 103 CFU/mL. Furthermore, the sample inoculated with 1 CFU/mL of A. acidoterrestris could be detected as positive after incubation for 24 h. The IMS–ELISA described, allows for the identification of suspect positive samples within 3 h of testing versus 3–5 days required by standard culture methods while significantly reducing the materials and labor required for the detection of Alicyclobacillus spp. in apple juice samples. As compared with the standard culture method performed concurrently on the same set of samples, the sensitivity, specificity and accuracy of IMS–ELISA for 102 naturally contaminated apple juice samples were 91.3%, 96.02% and 95.09%, respectively. These results demonstrated that the newly proposed IMS–ELISA procedure can be a potentially useful analytical method for the detection of Alicyclobacillus spp. in apple juice.