Assessment of Preparation Methods to Produce a Postharvest Spinach Wash Water Model for Sanitizer Validation Studies and Comparison of Sanitizer Quantitation Methods

Abstract

Currently no standard benchtop preparation method exists for simulated produce wash water, which makes it challenging to compare sanitizer efficacy reports and provide guidance for growers regarding water quality monitoring and free chlorine quantification. This work compares benchtop preparation methods for spinach-based model wash water (blender vs stomacher), metrics for organic load standardization (chemical oxygen demand (COD) vs nephelometric turbidity units (NTU)), and free chlorine quantitation methods (N,N-diethyl-p-phenylenediamine (DPD) vs iodometric titration (IOD)). It was found that COD is a more reliable metric for organic load standardization than NTU. Blender-and stomacher-generated wash water had similar physicochemical properties at organic loads up to 1000 mg/L COD, so both methods are acceptable, and DPD titration reflected expected patterns of free chlorine consumption in wash water more accurately than IOD. These results support the use of select wash water preparation and free chlorine detection methods, informing the development of a standardized protocol.