Dynamic changes in the physicochemical properties of fresh-cut produce wash water as impacted by commodity type and processing conditions

Authors: LI, JIE - Huazhong Agricultural University; TENG, ZI - University Of Maryland; WENG, SHIHCHI - Johns Hopkins University; SRINIVASAN, PARTHASARATHY - Cleveland State University; Zhou, Bin; Turner, Ellen; Luo, Yaguang - Sunny

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/22/2019
Publication Date: 9/26/2019
Citation: Li, J., Teng, Z., Weng, S., Srinivasan, P., Zhou, B., Turner, E.R., Luo, Y. 2019. Dynamic changes in the physicochemical properties of fresh-cut produce wash water as impacted by commodity type and processing conditions. PLoS One. https://doi.org/10.1371/journal.pone.0222174.
DOI: https://doi.org/10.1371/journal.pone.0222174

Interpretive Summary: Washing is essential to maintain quality and shelf life of fresh produce. Sanitizers, such as chlorine, should be maintained at proper levels during washing to prevent microbial contamination of produce. However, the build-up of organic matter in reused wash water makes it challenging to maintain stable chlorine levels because these materials react with chlorine, thus reducing chlorine levels in wash water. Water quality parameters, including pH, turbidity, total dissolved solids, sugar content and oxygen depletion due to reaction of organic matter with chlorine were monitored and compared for their abilities to predict needs for addition of fresh chlorine to wash water. All parameters increased with the repeated addition of products washed in the same tank of water, but at different rates dependent on commodity type and size of cut produce. These findings are useful in developing on-line chlorine dosing formulas to correctly predict and dose chlorine into wash systems to ensure effective control of microbial contaminants in produce wash water.

Technical Abstract: The accumulation of organic materials in fresh-cut produce wash water presents a major challenge for maintaining free chlorine concentration and sanitizing efficacy against pathogen cross-contamination. In this study, eight water quality parameters [chemical oxygen demand (COD), total organic carbon (TOC), total suspended solids (TSS), total dissolved solids (TDS), turbidity, total sugar content, pH, and chlorine demand (CLD)] were monitored as indicators for organic load during continuous washing of fresh-cut produce (carrot, Romaine lettuce, and Iceberg lettuce). The changes in these parameters as impacted by produce type, product/water ratio, and cutting sizes and shapes were characterized. Results indicate that the changes in pH were commodity dependent, while the values of all other parameters increased linearly with increased product-to-water rate and decreased cut size. Among all product types, shredded carrot resulted in the highest increase in COD, TOC, TDS, turbidity and sugar content, while Romaine lettuce led to the highest TSS. Compared to Iceberg lettuce, Romaine lettuce exhibited higher TOC, TSS, TDS, and turbidity, with similar COD and lower CLD, when washed at a same product-to-water ratio. Finally, all parameters except pH were significantly (p<0.01) correlated with CLD, and their pros and cons as CLD indicators in the wash water were discussed.