Characterization and Kinetic Study of Bentonite-Coated Activated Carbon for Adsorption of DNA Polymerase Inhibitors to Improve the Detection Sensitivity of Salmonella Derived from Vegetables by Rti-LAMP

Bentonite-coated activated carbon (BCAC) as an effective adsorbent can absorb soluble impurities in food to improve the detection sensitivity of Rti-LAMP assay. In the present study, BCAC was optimally prepared and characterized by SEM-EDS, FTIR, Raman spectrum, and pHPZC. The adsorptive kinetics and capacities of BCAC for four representatives, including indigo carmine (IC), tryptophan, thiamine, and tannic acid, were also determined. The results showed that the coating ratio between bentonite and 1.25–2 mm coconut shell activated carbon (AC) was 1:4 (g/g), which was the optimum process for the preparation of BCAC. The recovery rate of Salmonella was about 94.0 ± 8.9% after BCAC treatment. The lowest level of DNA consistent detection was that from 2 CFU/g Salmonella-contaminated lettuce and bean sprouts by the Rti-LAMP assay combined with BCAC treatment. The adsorption rate of BCAC to IC was 88.9%, which was much consistent with the pseudo-second-order kinetic as the R2 value of 0.993. The adsorption rate of BCAC to tryptophan was 86.4% in accordance with the pseudo-first-order kinetic equation as the R2 value of 0.957. Also, the adsorption rates of thiamine, tannic acid, and lettuce water-soluble compounds by BCAC were 83.1%, 24%, and 50%, respectively. The SEM-EDS image and FTIR analysis showed that the uniform bentonite layer was successfully coated on the porous structure of AC to form the BCAC. The Raman spectra and pHPZC data showed that the internal structure and chemical properties of the BCAC were not different from those of AC. Therefore, the BCAC had a strong adsorption capacity for DNA polymerase inhibitors of vegetables, but not for bacterial cells, which would greatly improve the sensitivity of LAMP for detection of food pathogens.