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

Abstract

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.

Acid resistance of Salmonella Typhimurium ATCC 14028 after desiccation stress during peanut storage

“…In the current study, at the end of the storage period (180 days), reductions of 2.60 log cfu/g in the Salmonella population inoculated on the peanut samples were observed. NASCIMENTO et al (2018) observed reported similar reduction rates for unblanched peanut kernels (a w = 0.54) and for roasted peanuts (a w = 0.39) inoculated with Salmonella Typhimurium and stored for 180 days at 28 ºC, 2.51 log cfu/g and 2.22 log cfu/g, respectively. Reductions of 3.13 log cfu/g after 7 days and 1.24 log cfu/g after 168 days were obtained in peanut butter (a w 0.29) inoculated with a pool of five Salmonella serotypes (Agona, Enteritidis, Michigan, Montevideo, and Typhimurium) and stored at 21 ºC (BURNETT et al, 2000).…”

“…Codex Alimentarius defines LMF as foods with water activity (a w ) ≤ 0.85 (CAC, 2015). In a previous study, this pathogen was recovered from raw in-shell peanuts (a w 0.29) and unblanched peanut kernels (a w 0.54) after 240 and 330 days of storage at 28 °C, respectively (NASCIMENTO et al, 2018). In peanut hull compost mixture, Salmonella survived for 6 weeks (ERICKSON et al, 2015), and in peanut butter and peanut butter spreads (a w 0.20 and 0.30) for at least 24 weeks (BURNETT et al, 2000).…”

“…After the inoculation step, the sample was fractionated into three portions of 400 g, transferred to sterile plastic bags (Twirl'em, Labplas, Canada), and were stored in desiccators containing potassium carbonate solution (a w 0.43) (NASCIMENTO et al, 2018). The desiccators were kept in a bacteriological incubator (FANEM, mod 347 CD, Brazil) at 28 ºC for up to 180 days.…”

“…CALHOUN et al (2013) verified a Salmonella positive rate of 1.63% of raw shelled peanuts, with counts ranged from <0.03 and 2.4 MPN/g. In Brazil a rate of 2.21% of Salmonella contamination in peanut samples throughout the production chain, with counts between 0.004 and 2.4 MNP/g was reported (NASCIMENTO et al, 2018). Nevertheless, it is important to emphasize that even though S Typhimurium ATCC14028 has been used in studies involving LMFs (PEREIRA et al, 2020; NASCIMENTO et al, 2018;ROSSBACH et al, 2017;MATAK et al, 2010) other serotypes and strains need to be screened for their ability to develop cross-protection in this type of matrix.…”

Growth and thermal inactivation of Listeria monocytogenes and Escherichia coli O157:H7 in four kinds of traditionally non‐fermented soya bean products

“…Thermal resistance of L. monocytogenes in the four soya bean products may be related with the A w of food matrices, and δ‐values of L. monocytogenes reduced with A w of soya bean products decreasing. The protection mechanisms of bacteria are activated with the reduction of A w in the environment, such as osmoregulation which can balance the internal composition of cell with the external environment, which could enhance their thermal resistance (Nascimento et al ., 2018). In the study involved stability of L. monocytogenes in wheat flour at 70 °C, D 70 ‐values of L. monocytogenes were 37.10, 17.44 and 16.85 min in samples with A w of 0.30, 0.45 and 0.60, respectively (Taylor et al ., 2018).…”