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United States Department of Agriculture

Agricultural Research Service

Research Project: MICROBIAL FOOD SAFETY OF FRESH AND FRESH-CUT PRODUCE Title: Wash operations affect water quality and packaged fresh-cut romaine lettuce quality and microbial growth

Author
item Luo, Yaguang

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 20, 2007
Publication Date: September 24, 2007
Citation: Luo, Y. 2007. Wash operatons affect water quality and packaged fresh-cut romaine lettuce quality and microbial growth. HortScience. 42(6):1413-1419.

Interpretive Summary: Recent food-born illness outbreaks associated with the consumption of fresh-cut produce highlight the importance of ensuring food safety of fresh-cut fruits and vegetables. Produce wash is an important step commonly employed by the industry to maintain the quality and safety of fresh and fresh-cut produce. However, little information exists as to how wash operation and water re-use affect water quality, the efficacy of sanitizers on the reduction of microorganisms, or the quality and shelf life of packaged products. This study examined the effect of produce wash parameters, including simulated water re-use and re-circulation, and the ratio between product weight and wash water volume on the water quality and effectiveness of sanitizers available for bacterial inactivation, as well as their effects on the packaged product quality and microbial growth. We found that water re-use causes a rapid loss of water quality; fresh-cut Romaine lettuce washed with clean and high quality water in a small product to water ratio maintained the highest quality with less off-odor development and slower growth of lactic acid bacteria. This information is important to the produce industry in designing wash operations to achieve maximum reduction of microorganisms and maintain product quality and shelf life.

Technical Abstract: Washing during the preparation of fresh-cut produce is an important step to maintaining the quality and safety of the finished products. It is often the only step aimed at reducing microbial populations and removing tissue fluids from cut produce. However, little is known about the effects of washing method on the changes in water quality and its subsequent effects on microbial growth and finished product quality. This study was conducted to evaluate the effect of wash water re-use on changes in water quality in terms of chemical oxygen demand (COD), biological oxygen demand (BOD), salinity, total dissolved solids (TDS), total and free chlorine, as well as their subsequent effect on microbial growth and product quality of packaged fresh-cut romaine lettuce (Lactuca sativa L.). Romaine lettuce leaves were sliced and washed in water of different quality, and with different product to water ratio. Microbial growth and product quality were monitored at days 0, 4, 8, 11 and 14 at 5 °C. Results indicate that as the quantity of lettuce dipped in the same water increases, there is a rapid increase in water COD, BOD, salinity, and a rapid decline in free and total chlorine levels. Packaged fresh-cut lettuce washed with re-used water of high COD and BOD had more off-odor development, and rapid decrease in tissue integrity, although visual appearance was not affected. Thoroughly washed lettuce in clean water with a small product to water ratio had the lowest off-odor development. Samples without wash treatment and those washed with re-used water had the largest growth of lactic acid bacteria. These results indicate that it is critical to maintain water quality in order to maintain product quality.

Last Modified: 12/18/2014
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