Immersion-free, single-pass, commercial fresh-cut produce washing system: an alternative to traditional flume processing

Authors: BORNHORST, ELLEN - Orise Fellow; Luo, Yaguang - Sunny; Park, Eunhee; Vinyard, Bryan; Nou, Xiangwu; Zhou, Bin; Turner, Ellen; Millner, Patricia

Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/18/2018
Publication Date: 9/11/2018
Citation: Bornhorst, E.R., Luo, Y., Park, E., Vinyard, B.T., Nou, X., Zhou, B., Turner, E.R., Millner, P.D. 2018. Immersion-free, single-pass, commercial fresh-cut produce washing system: an alternative to traditional flume processing. Postharvest Biology and Technology. 146:124-133.

Interpretive Summary: Commercially processed ready-to-eat, fresh-cut produce typically is washed by submersion in large tanks of chlorinated water. Due to the need to conserve water and reduce costs, wash water is often reused, making this process prone to microbial cross-contamination and spread of harmful bacteria, especially when the level of chlorine or other sanitizers falls below a critical limit. A new washing process using multiple water sprayers with single pass water (water that is not reused), may have the potential to reduce pathogen cross-contamination. However, the effect of this new washing system on product quality is unknown. In this study, USDA-ARS research scientists conducted experiments in a commercial produce fresh-cut processing facility to compare the chemical and microbiological quality of the wash water, and the quality of the produce from two washing systems: (1) the novel spray wash process with single pass wash water and (2) a traditional wash tank process. Results showed that the novel spray system controlled water quality more effectively and produced fresh-cut lettuce and cabbage that had equal or better quality than corresponding products from the conventional wash tank process. The results from this research provide critical information for researchers and commercial fruit and vegetable processors that can be used to optimize washing processes and develop new innovations to improve the safety and quality of ready-to-eat produce.

Technical Abstract: Conventional fresh-cut produce processing involves submerging produce in chlorinated water that is re-circulated in a series of flumes. However, this standard washing practice is water and chemical intensive and subject to rapid decreases in free chlorine concentration, which can increase the risk of cross-contamination. An immersion-free, produce washing system was recently developed to address these challenges by over-head spraying clean (retreated) water, rather than spent wash water. The objective of this study was to compare single-pass and flume systems during commercial processing of fresh-cut lettuce and cabbage. Processes were monitored on three separate days for both products; wash water and produce were sampled every 30 min for 2.5 h. Wash water samples were collected from the flume (flume A, catch tank A, flume B, catch tank B) and single-pass (input water, pre-wash, cutter, incline wash, vibra-wash) systems. Physicochemical (free chlorine, total chlorine, pH, total dissolved solids (TDS), chemical oxygen demand (COD), turbidity) and microbial analyses (aerobic plate count (APC)) were conducted on the wash water samples. Produce samples were collected after cutting and packaging; samples were analyzed for APC and sensorial quality (visual, olfactory, overall acceptability) during three weeks of storage by a trained panel. Results show that the organic load (turbidity, TDS, COD) in wash water samples from the flume system increased over time, but was consistent in samples from the single-pass system. For the single-pass system, the wash water from the cutter had the largest APC and the highest organic load compared to that from all other processing stages. There were no significant differences in APC between flume and single-pass washed lettuce or cabbage tissue samples. Panelists rated the quality of the products washed using the single-pass system as good as, or better than flume-washed products during the three-week shelf life study. Under these testing conditions, the single-pass system washing system had better controlled wash water organic load, similar product microbial levels, and equal or better sensorial quality during storage compared to the flume system. Results from this study could be used to further optimize the single-pass system and develop additional processing innovations.