Scientists at the University of Illinois have found a way to create safer spinach plants by reducing the number of E. coli bacteria present on leaves. Over the past twenty years, the first cases of E. coli contamination from vegetables have occurred; E. coli rose to prominence as a serious threat to human health in the 1980s, having previously existed in the guts of warm-blooded animals including cattle.

Since 1995, when the first E. Coli outbreak was linked to lettuce and Spinach growing operations in the Salinas Valley, one of California’s most productive agricultural regions, numerous outbreaks have been traced back to bacteria thriving undetected on vegetable leaves.

University of Illinois researcher Hao Feng said, "By combining continuous ultrasound treatment with chlorine washing, we can reduce the total number of foodborne pathogenic bacteria by over 99.99 percent." According to Feng, the USDA is looking for proposed technologies that can achieve dramatic reductions in pathogen cells.

He said his tested method is up to four times as effective as current industry techniques.  Dr Feng added, "Combining technologies is the key to bridging the gap between our current capacity and what USDA would like to see. The use of ultrasound exposure during chlorine washing gives the industry a way to significantly enhance microbial safety."

Although Dr Feng's approach may sound radical, it is necessary to avoid contamination with bacteria which are becoming more of a serious threat around the world. US spinach growers are estimated to have lost $20 million in 2006 alone as a result of fears over E. coli.

Dr Feng elaborated on his work, "Previous work with ultrasound used a tank or a medical-style probe, which doesn't provide consistent and even distribution." He also noted that system design is important for another reason, "Placement of the produce as it makes its way through the channel turns out to be very important. We had to find ways to make sure that leaves received similar exposure to ultrasound, taking care to minimize the chance that one leaf would block a nearby leaf's exposure to the sound waves."

If even part of a leaf escaped the full ultrasonic treatment, it could contaminate the rest of the produce, he said. Feng and his team have used the technique on iceberg and romaine lettuce as well as spinach with similar results.

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