Impacts and interactions of organic compounds with chlorine sanitizer in recirculated and reused produce processing water

Authors: TENG, ZI - UNIVERSITY OF MARYLAND; VAN HAUTE, SAM - U.S. FOREST SERVICE (FS); Zhou, Bin; Hapeman, Cathleen; Millner, Patricia; WAMG, QOM - UNIVERSITY OF MARYLAND; Luo, Yaguang - Sunny

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/27/2018
Publication Date: 12/12/2018
Citation: Teng, Z., Van Haute, S., Zhou, B., Hapeman, C.J., Millner, P.D., Wamg, Q., Luo, Y. 2018. Impacts and interactions of organic compounds with chlorine sanitizer in recirculated and reused produce processing water. PLoS One. 13(12):1-15.

Interpretive Summary: The increasing demand for healthy and convenient foods over the past few decades has resulted in considerable growth of the fresh-cut produce industry. To market the product “ready-to-eat”, the fresh-cut produce usually undergoes a triple wash process, but for every ton of produce cleaned, three to five tons of water is used. Thus, to conserve the water, it is reused and chlorine is replenished as needed to ensure food safety. During processing of fresh-cut vegetables, organic compounds are released from the vegetables into the water, complicating the reuse of the wash water because they can also react with and increase the requirement for chlorine (also known as chlorine demand). We conducted a series of experiments to examine the profile of the released compounds from fresh-cut vegetables and to determine their effect on chlorine demand. Results showed that sugars are the most abundant component in the wash water, but the chlorine demand is low because the reactivity of sugar with chlorine is limited. On the other hand, components with low concentrations, such as proteins, peptides, acids, and phenols, had high chlorine demand. This systematic report provides essential information useful in the development and evaluation of water treatment procedures for the fresh-cut produce industry and will lead to improvements in the overall food quality and safety of fresh-cut produce.

Technical Abstract: Water conservation and economics dictate that fresh produce processors reuse/recirculate the process water. The presence of organic matter in this reused wash water depletes the concentration of chlorine sanitizer required for food safety. The lack of scientific information regarding the groups of compounds responsible for water quality deterioration significantly limits development of water and process control strategies to maintain sanitizer efficacy. Thus, in this study, we used diced cabbage as a model product to identify which organic compounds contribute to chemical oxygen demand (COD) and chlorine demand (CLD), the two most critical factors associated with water treatment and chlorine replenishment. Simulating commercial fresh-cut wash operations, multiple batches of diced cabbage (0.3 x 0.3 cm2) were washed in the same tank of water. The major organic chemicals were identified and quantified by HPLC and comparison to known standards. Sugars were the predominant compounds (82.7% dry weight) and the major contributor to COD (81.6%), followed by proteins/peptides (7.3% dry weight, 5.3% COD), organic acids (6.2% dry weight, 3.6% COD), and phenolics (0.5% dry weight, 0.5% COD). By repeated time course measures, the effect of these chemicals on CLD are dependent on the chemical structure, concentration in the wash water, and their rate of reaction. Proteins/peptides accounted for about 50% of the total CLD over a 120-min period and phenolics was 21% at 5 min, but diminished with time. The contribution by organic acids and sugars increased continuously, reaching 22% and 16% of total CLD at 120 min of chlorination, respectively. Collectively, these compounds represented 86% of the CLD in cabbage wash water at 5 min and greater than 94% CLD afterwards. This is the first systematic report on the source of COD and CLD during fresh produce washing, and it provides essential information for the produce processors to develop safe, effective, and economical wash water treatment/reuse and chlorine replenishment strategies.