Microbiological contamination in peanut confectionery processing plants

Effects of peanut drying and blanching on Salmonella spp

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 (T_3d) and 5-log reduction (T_5d) 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.

Long-term kinetics of Salmonella Typhimurium ATCC 14028 survival on peanuts and peanut confectionery products

Due to recent large outbreaks, peanuts have been considered a product of potential risk for Salmonella. Usually, peanut products show a low water activity (aw) and high fat content, which contribute to increasing the thermal resistance and survival of Salmonella. This study evaluated the long-term kinetics of Salmonella survival on different peanut products under storage at 28°C for 420 days. Samples of raw in-shell peanuts (aw = 0.29), roasted peanuts (aw = 0.39), unblanched peanut kernel (aw = 0.54), peanut brittle (aw = 0.30), paçoca (aw = 0.40) and pé-de-moça (aw = 0.68) were inoculated with Salmonella Typhimurium ATCC 14028 at two inoculum levels (3 and 6 log cfu/ g). The Salmonella behavior was influenced (p<0.05) by aw, lipid, carbohydrate and protein content. In most cases for both inoculum levels, the greatest reductions were seen after the first two weeks of storage, followed by a slower decline phase. The lowest reductions were verified in paçoca and roasted peanuts, with counts of 1.01 and 0.87 log cfu/ g at low inoculum level and 2.53 and 3.82 log cfu/ g at high inoculum level at the end of the storage time. The highest loss of viability was observed in pé-de-moça, with absence of Salmonella in 10-g after 180 days at low inoculum level. The Weibull model provided a suitable fit to the data (R2≥0.81), with δ value ranging from 0.06 to 49.75 days. Therefore, the results demonstrated that Salmonella survives longer in peanut products, beyond the shelf life (>420 days), especially in products with aw around 0.40.