Vacuum packaging improved inactivation efficacy of moderate dry heat for decontamination of Salmonella on almond kernels

The goal of this study was to develop dry heat processing conditions that could achieve a >5-log reduction of Salmonella with minimal negative impact on almond quality. The effects of almond's water activity (a_w) levels and packaging methods on Salmonella inactivation by dry heat were determined. Almonds were dip-inoculated in a four-strain Salmonella cocktail and conditioned to a_w of 0.43, 0.33, 0.23, and 0.20. The inoculated almonds were then placed in vacuum-sealed mylar bags (vacuum packaging), ambient-sealed glass tubes (non-vacuum packaging), and petri dishes without covers (no packaging). The packaged and un-packaged almonds were treated by dry heat with 13 % relative humidity at 73 °C. Vacuum packaging in general achieved slightly better (in some cases significantly better (p < 0.05)) or similar inactivation effect on Salmonella than non-vacuum packaging. Both vacuum and non-vacuum packaging methods achieved much greater Salmonella inactivation than the no packaging method. For example, a 4-h treatment at 73 °C reduced Salmonella on almonds with a_w of 0.43 by 5.1-, 4.4-, and 1.3-log for mylar bag, tube, and petri dish, respectively. Higher a_w levels resulted in better inactivation of Salmonella. To achieve a >4-log reduction of Salmonella on almonds packaged in mylar bags, 3-, 6-, 8-, and 8-h of heat treatment were needed for almonds with a_w values of 0.43, 0.33, 0.23 and 0.20, respectively. Vacuum packaging in combination with a 4-h heat treatment of almonds with initial a_w of 0.43 or 8-h heat treatment of almonds with initial a_w of 0.33 could achieved a ≥5-log reduction of Salmonella. Those two combinations resulted in very little weight loss (≤0.05 %), insignificant color change (∆E ≤ 1.26), and unnoticeable change in visual appearance of almonds, demonstrating that they could be potentially used for raw almond pasteurization.