Practical applications of sensor-based methodologies for monitoring peracetic acid (PAA) as a disinfectant of fresh produce wash water

Abstract

An accurate sensor for peracetic acid (PAA) is needed to monitor and control the disinfection of fresh produce wash water. Inaccurate measurements can result in underdosing and unsafe produce or overdosing with huge cost implications. In this study, five methods were compared for measuring PAA in process water from washing apples, tomatoes, red sweet peppers, and lemons. A reversed phase HPLC-DAD method for the determination of PAA in water was adapted for process wash water and used as a reference method. The results showed that HPLC offered high selectivity for PAA and precise and reproducible measurement for its quantification. However, as HPLC is not suitable for in-line applications in processing plants and requires highly skilled technicians, installation and maintenance costs, other analytical methods were examined including a redox titration, a reflectometric method and two electrochemical methods (an amperometric in-line probe and a chronoamperometric method with disposable single-use electrode sensor). The drop titration kit overestimated PAA because of the interferences from other oxidizing agents such as hydrogen peroxide (HP) apart from it required substantial time to perform the measurements plus the extensive training of the technical personnel to ensure confidence in the results. The reflectometric method with disposable test strips, although fast and objective, overestimated PAA due to the wash water with a high content of suspended organic matter that needed the addition of high concentrations of PAA, coexisting with HP. From the two electrochemical methods studied, the in-line amperometric sensor underestimated the PAA concentration in lemon wash water as the PAA could not freely diffuse through the membrane through the active electrode because of the organic matter present in the wash water released from the lemon peel. In contrast, the chronoamperometric sensor showed good selectivity for PAA without interferences, with reliable results across all the wash water types and PAA concentrations.