Salmonella and Other Enterobacteriaceae at Peanut Processing Stages

Introduction: Due to recent outbreaks, peanuts have been considered a product of potential risk for Salmonella. In spite of this, little is known about the occurrence of Salmonella in peanut processing. Due to recent outbreaks, peanuts have been considered a product of potential risk for Salmonella. In spite of this, little is known about the occurrence of Salmonella in peanut processing. 

Purpose: The aim of this study was to investigate the presence of Enterobacteriaceae, coliforms, Escherichia coli and Salmonella in peanuts during processing stages (drying, shelling, sorting, blanching, roasting) in Brazil.

Methods: One hundred samples from six processing plants were analyzed. Salmonella detection was carried out in 250 g of each sample by an immunoassay method - Mini-Vidas System. Enterobacteriaceae was enumerated in Violet Red Bile Agar with Glucose (VRBG), and Petrifilm 6404 was used for total coliforms and E. coli. The pH value and the water activity (a_w) of the samples were also determined.

Results: The a_w of the media was reduced to < 0.56 after drying and to < 0.35 after roasting step. The pH values ranged from 5.91 to 7.13. Samples showed Enterobacteriaceae counts between < 1 and 7.98 log CFU/g. The highest total coliform counts (7.32 log CFU/g) were observed before the drying step. E. coli was not detected in any analyzed sample, whereas Salmonella was isolated in two samples (0.004 MPN/g) collected during drying in the same processing plant.

Significance: Therefore, the results show that peanuts could be contaminated by Salmonella during post-harvest stages. This reinforces the importance of a well-designed roasting step to obtain a safe final product.