Safety Assurance of Pecans by Irradiation without a Detrimental Effect on Quality

Pecan nuts might become contaminated with foodborne pathogens, such as Salmonella and E. coli., through birds and other potential sources of contamination that can lead to serious illness or even death, as well as financial losses. For example, the outbreak of Salmonella in pecan products in Texas caused major product recalls in 2010. Irradiation with electron beams could be an effective method of preventing potential outbreaks without changing the pecans' taste, color and flavor and without causing any risk of recontamination before the product reaches the consumer. However, when irradiation is applied alone, the shelf life of the product is decelerated because of the detrimental effect of lipid oxidation. Therefore, to extend the shelf of the pecans while assuring their safety, irradiation of pecans under modified atmosphere packing (MAP) conditions could be a viable option.

This research showed that when treated with electron beams, surrogates of Escherichia coli (a cocktail of BAA-1427, BAA-1428, and BAA-1430), and Salmonella (S. Typhimurium LT2) were more resistant to ionizing radiation (higher D10 values) when packed under vacuum (VP) than under air or other MAP conditions.

This research also showed that lipid oxidation in pecans (due to exposure to ionizing radiation) shows a lag phase, probably due to the antioxidants present in pecan nuts. The lag phase represents a delay period before the pecan nuts start to get rancid (increase in PV formation), and it is best described by a modified Gompertz model. Kinetic evaluation of the lipid oxidation reaction suggests that the dose level has a more drastic effect in PV formation than the type of package used during the irradiation treatment, e.g., vacuum packed versus nitrogen-packed.

Moreover, accelerated shelf life studies (4 weeks at 48.9oC) showed that vacuum-packed (VP) pecans can be stored at -25 degrees C up to three years, while irradiated (at 3.0 kGy) VP pecans can be stored only for eight months, without the detrimental effects of lipid oxidation. Therefore, irradiation of pecans under air at 3.0 kGy reduces the shelf life of the nuts in terms of rancidity, but vacuum-packaging can be used to extend their shelf-life. Irradiation in oxygen packaging increases rancidity and the oxidation reaction rate accelerates with increasing dose. Irradiation under nitrogen packaging requires lower doses to achieve the almost same number of log reductions in microbial population. The use of nitrogen packaging also inhibits the oxidative reaction leading to rancidity in pecans. Although there are some drawbacks to the application of nitrogen packaging in an irradiation plant (special machinery and packaging films (permeability specifications for N2 gas)), the savings induced by avoiding recalls may make this technology worthy of consideration.