Researchers from the US Department of Agriculture’s Agricultural Research Service (ARS) are confident that the method, which has been dubbed SIRHA (sequential infrared and hot air), can be scaled up for commercial use in processing and packaging facilities.
Almonds are not typically contaminated with high levels of Salmonella, but almonds for sale in the US must be pasteurised in order to reduce potentially hazardous levels of the pathogen.
The method has to be powerful enough to reduce Salmonella population levels 10,000 fold (4-log), to level that are generally regarded as safe.
Using the SIRHA technique, the researchers were able to exceed the 4-log minimum Salmonella reduction – achieving results of 5.8-log.
Infrared and hot air
The investigation, which is being conducted by California-based researchers Zhongli Pan and Maria Brandl, compared the effectiveness of three approaches – conventional hot air heating, infrared heating, and infrared heating followed by hot-air heating (SIRHA).
Throughout the study, the researchers used the bacterium Enterococcus faecium, which offers the same heat resistance as Salmonella enterica.
Pan and Brandl were able to established that SIRHA was more energy efficient than the singular methods – offering potential time and money saving benefits to processors.
The SIRHA methods involves heating the almonds using infrared emitters – above and below the product - for around one minute until they reached a surface temperature of 140°C.
The nuts were then roasted with hot air at the same temperature for around 11 minutes.
The researcher’s batch-based processes could be upgraded to a continuous flow regime, making it suitable for conveyor-belt-based processing – the standard at most almond packing facilities.
Several processors have expressed an interest in the studies, according to the researchers.
Pan told ARS, infrared heating “doesn’t require use of any chemicals and offers a simple, safe, energy-efficient, and environmentally friendly way to kill Salmonella while almonds are still at the packinghouse.”
“We exposed the almonds to a quick burst of infrared heat, allow their surface temperature to drop, then keep them at that temperature until we reach the target kill rate.”
“We used a batch process, but it should be easy to replicate our kill rate in a continuous-flow system at the packinghouse,” Pan added.