Amperometric screening of bacterial food contamination using a composite modified electrode

An indirect determination of bacterial contamination based on catabolic metabolism of glucose is proposed. The determination of glucose was carried out by a flow injection (FI) system with amperometric detection using a wall-jet flow cell. A new composite PVC–graphite electrode modified with Cu2O was developed to improve the analytical features of glucose determination. A 25 mM saline buffer sodium phosphate in 0.2 M NaOH was used as the carrier for glucose. After optimising the sensing electrode in terms of composite electrode formulation, hydroxide ion concentration and operating potential, the detection limit for glucose was 1.1×10^-3 M for 100 (mu)l injections. The proposed method allows the successful determination of pollution bacteria in food samples in 3 h as compared to the 24–48 h required using the plate count method. The detection limit for bacteria in the samples was 2×10^2 cfu ml^-1 and the reproducibility was in the range 2.6–3.8%. The efficiency of this method was tested for eight types of bacteria and five kinds of food. A comprehensive study of 30 spiked samples and 30 blank samples provided 4% of false positives and 0% of false negatives showing the applicability of the proposed method for sample screening.