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Electrostatic spray of organic acids, grape seed extract decontaminates E. coli on spinach.

Multi-state outbreaks of E. coli O157:H7 infections from fresh spinach were reported in 2006 in 26 states across the United States, reinforcing a need to find antimicrobial interventions that would control the amount of E. coli in spinach.

Scientists at the University of Arkansas wanted to see if an electrostatic spray consisting of tartaric (TA) and malic (MA) acids and grape seed extract (GSE) would be a good intervention technology for controlling the bacteria in spinach. They compared the effectiveness of the electrostatic spray with conventional spray and dipping techniques. They found that the electrostatic spraying of TA, MA and GSE can efficiently inhibit E. coli on spinach in comparison to conventional techniques. The key: electrostatic spraying creates a uniform deposition of antimicrobials onto the product's surface.

The researchers washed spinach samples and dipped them in a sodium hypochlorite solution (6.25 ml per L). The mixture was washed with sterile deionized water. Ten ml of a second-day culture of E. coli O157:H7 was transferred to 6 L of sterile phosphate buffer saline (PBS). The spinach samples were dipped in this mixture for 24 hours at 37 C.

After 24 hours, the inoculated spinach was washed to remove unattached bacteria. This spinach was sprayed with and dipped in an antimicrobial test solution. Any excess solution was allowed to drip in a beaker, then air-dried and stored at 4 C. On the day of testing, the spinach samples were transferred into a commercial sample bag. They were ground, serially diluted and plated in MacConkey sorbitol agar supplemented with Cefixime Tellurite.

Results showed that electrostatic sprays of 2% TA and 2% GSE, and 2% MA and 2% GSE, led to greater reductions in log numbers of the E. coli (3.3 to 3.6 and 1.5 to 3.8 log CFU per g, respectively) than did the control (6.8 to 7.5 logs CFU per g). Conventional spraying did not stop the growth of surviving E. coli. Dipping the samples caused less inhibition or killing of the bacteria during the storage of the samples.

Further information. Navam S. Hettiarachchy, Department of Food Science, University of Arkansas, 2650 N Young Ave., N-218, Fayetteville, AR 72704; phone: 479-575-4779; fax: 479-575-6936; email:
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Publication:Microbial Update International
Date:Feb 1, 2009
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