Effects of peanut drying and blanching on Salmonella spp.

Abstract

In order to evaluate the behavior of Salmonella during peanut drying and blanching, a study was conducted with Runner type peanuts. Samples of raw in-shell or unblanched peanuts were inoculated by spraying with a pool of five Salmonella serotypes isolated from the peanut supply chain (Miami, Muenster, Yoruba, Javiana and Glostrup). The in-shell peanuts were submitted to drying at 35 and 40 °C up to 18 h. After this time, the Salmonella counts went down ca. 2.0 log MPN/g at 35 and 40 °C. According to the Weibull model the time needed to achieve Salmonella 3-log reduction (T3d) and 5-log reduction (T5d) on the in-shell peanuts would be ca. 49 and 117 h at 35 °C and 35 and 79 h at 40 °C, respectively. The results showed that there was no statistical difference (p > .05) between either of the temperatures employed in the process. The blanching process was performed in two steps: pre-roasting (step 1) and skin removal (step 2). Reduction of up to 2.1 log MPN/g was observed after blanching at 100 °C/15 min plus 15 s of air impact. The skin removal process did not result in recontamination of the final sample. The Weibull model predicted 3- and 5-log reductions of Salmonella in 37.0 and 68.9 min for blanching at 95 °C, and in 39.1 and 114.9 min at 100 °C. The results demonstrated that drying and blanching processes did not generate large reductions of Salmonella in the peanut samples. Thus, the product resulting from these steps may be a possible source of cross-contamination for the processing plant and the final product.