Factors impacting water quality and microbiota during simulated dump tank wash of grape tomatoes

Authors: Zhou, Bin; Luo, Yaguang - Sunny; TENG, ZI - University Of Maryland; Nou, Xiangwu; Millner, Patricia

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2020
Publication Date: 12/3/2022
Citation: Zhou, B., Luo, Y., Teng, Z., Nou, X., Millner, P.D. 2022. Factors impacting water quality and microbiota during simulated dump tank wash of grape tomatoes. Journal of Food Protection. 84:695-703. https://doi.org/10.4315/JFP-20-343.
DOI: https://doi.org/10.4315/JFP-20-343

Interpretive Summary: Varying quantities of tomato leaf-stem debris and damaged fruits are often harvested along with high quality fruits, especially when the fruits are harvested by untrained fruit pickers and during labor shortage. This could pose a big challenge for tomato packinghouses to maintain sufficient free chlorine concentration and keep spoilage microorganisms and pathogens out of the dump tank wash water. This study examined the relationship between tomato harvest quality factors and wash water quality. Results demonstrate that, while water quality deteriorated proportionally to the cumulative quantity of tomatoes and debris present, field debris and damaged fruits contributed to the majority of the organic load and microbial bioburden in wash water. Results highlight the importance of minimizing the presence of field debris and defective fruits during tomato harvesting for maintaining packing house dump tank wash water microbial quality and operation efficiency. Findings will benefit tomato fruit growers, harvesters, and packing house operators for developing science-based best practices.

Technical Abstract: Multiple salmonellosis outbreaks in the USA have been associated with contaminated tomatoes. Scientific information is critically needed to develop an effective, practical food safety standard for the tomato industry. The aim of this study was to assess factors impacting the deterioration of tomato fruit wash water quality and survival of indigenous microorganisms during a simulated dump tank washing process. Freshly harvested grape tomatoes (3 kg) were sorted into four groups: prime, defective, under-ripe, and debris. Tomato fruits with leaf-stem harvest debris, combined or separately, were washed in tap water (chlorinated or not), and water samples were collected and analyzed for common wash water quality parameters (total dissolved solids, turbidity, chemical oxygen demand, and chlorine demand). Microbial populations (aerobic bacterial and yeast-mold plate counts) in water and on tomatoes as impacted by chlorine concentration and water filtration (300 µm) were also determined. Results showed that field debris and defective tomatoes were the major contributors of microbial counts in wash water. Water quality deterioration was proportional to the cumulative quantity of tomatoes and debris washed per minute. Chlorine demand was lower than 75 mg/L when the cumulative ratio of tomato-to-water reached 1.2:1. Field debris, which accounted for <1% of the total weight of tomato harvest, contributed 37.84% of total dissolved solids, 46.15% of turbidity, 48.77% of chemical oxygen demand and 50.55% of chlorine demand in the wash water. This study shows that technologies and/or practices that minimize the presence of field debris and defective fruits from harvested grape tomatoes can significantly reduce the microbial load and deterioration of water quality in post-harvest tomato washing. This information is beneficial to the development of data-driven packinghouse food safety practices for grape tomatoes.