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Reduce S. enteritidis on treated whole almonds.

Raw almonds are an excellent source of protein, vitamins, minerals and essential fatty acids. They are also high in calcium, iron, potassium, phosphorus and trace minerals, such as zinc and copper. Unfortunately, outbreaks of Salmonella enterica serotype Enteritidis infections have been associated with raw almonds.

Scientists at California's Almond Board and colleagues elsewhere evaluated the thermal inactivation of S. enteritidis phage type 30 using dry heat on pre-wet and acetic acid-treated almonds. Their effort indicates that an acetic acid treatment that's followed by a water rinse and dry heat treatment at 300 F for 10 minutes can significantly reduce levels of S. enteritidis. Exposing pre-wet almonds in a 300 F oven for 10 minutes reduced Salmonella by 3.2 logs. The reduction reached more than 5 logs if the wetting agent was 10% acetic acid solution.

The researchers inoculated the almonds with S. enteritidis at 7 log CFU per g. The inoculated almonds were treated with sterile water (5% w/w) or 10% acetic acid solution for 2 minutes. Then they were rinsed with water. The almonds were stored at ambient temperature for 60 minutes and exposed to dry heat at 250 F and 300 F in an isotemp oven.

The scientists pulled the samples after they were heated for 4, 8 and 20 minutes at 250 F, and after 2.5, 5 and 10 minutes at 300 F. Some of the acetic acid-treated samples were pulled after 20 minutes at 250 F, and 10 minutes at 300 F. They were kept at ambient temperature for three days.

Researchers analyzed the almonds for S. enteritidis using the pour plate technique with non-selective tryptic soy agar that had a selective xylose lysine desoxycholate agar overlay. The plates were incubated at 35 C for 48 hours. At 250 F after 20 minutes, counts of S. enteritidis were reduced by 2.24 log CFU per g on the pre-wet almonds, and by 3.09 and 2.94 log CFU per g on the acetic acid-treated almonds chilled to ambient temperature and stored at ambient temperature for three days, respectively.

At 300 F after 10 minutes, counts of S. enteritidis were reduced by 3.50 log CFU per g on the pre-wet almonds. They were reduced by 4.78 and 4.11 log CFU per g on the acetic acid and water-rinse treated almonds chilled to ambient temperature and stored at ambient temperature for three days, respectively. Note that the results were based a lab-scale oven.

Further information. Guangwei Huang, Almond Board of California, 1150 Ninth St., Suite 1500, Modesto, CA 95354; phone: 209-549-8262; fax: 209-549-8267; URL:
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Publication:Microbial Update International
Date:Feb 1, 2007
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