Ultrasound key to safer spinach

Friday, 30 November, 2012

Ultrasound could be the key to reducing Escherichia coli on spinach leaves. University of Illinois (U of I) scientists have developed a method that boosts current industry capabilities when it comes to reducing the number of E. coli O157:H7 cells that can live undetected on spinach leaves.

“By combining continuous ultrasound treatment with chlorine washing, we can reduce the total number of foodborne pathogenic bacteria by over 99.99%,” said Hao Feng, a professor of food science and human nutrition at U of I.

The USDA is seeking proposed technologies that can achieve a 4- to 6-log reduction in pathogen cells. To put this into perspective, a 6-log reduction would achieve a million-fold reduction in pathogenic bacteria. Currently, the food processing industry can achieve a 1-log, or tenfold, reduction. In comparison, the U of I method yields a 4-log reduction.

“Combining technologies is the key to bridging the gap between our current capacity and what USDA would like to see,” Feng said. “The use of ultrasound exposure during chlorine washing gives the industry a way to significantly enhance microbial safety.”

Feng used three pairs of large-area ultrasonic transducer boxes to form a channel through which ultrasound is provided to spinach leaves while they are undergoing a continuous-flow chlorine wash. The scientists used metallic foil to confirm spatial uniformity of the ultrasound distribution. Feng says previous studies with ultrasound have used a tank or medical-style probe, which doesn’t provide consistent and even distribution.

“Placement of the produce as it makes its way through the channel turns out to be very important,” Feng said. “We had to find ways to make sure that leaves received similar exposure to ultrasound ...”

If the full ultrasonic treatment didn’t reach all parts of a leaf, Feng said, the contaminated part of the leaf could affect the rest of the produce. The technique has been used on iceberg and romaine lettuce with similar results.

The research team’s findings were published in Innovative Food Science and Emerging Technologies. Co-authors of the paper were U of I researchers Bin Zhou and Arne J Pearlstein. Funding was provided by Food Technology Noord-Oost Nederland, with additional support from the USDA.

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