Comparative evaluation of the effectiveness of alcohol-based sanitizers, UV-C radiation and hot air on three-age Salmonella biofilms.

Dry sanitation is recommended to control contamination and prevent microbial growth and biofilm formation in the low-moisture food manufacturing plants. The objective of this study was to evaluate the effectiveness of dry sanitation protocols on Salmonella three-age biofilms formed on stainless steel (SS) and polypropylene (PP). Biofilms were formed for 24, 48 and 96 h at 37 °C using a cocktail of six Salmonella strains (Muenster, Miami, Glostrup, Javiana, Oranienburg, Yoruba) isolated from the peanut supply chain. Then, the surfaces were exposed to UV-C radiation, hot air (90 °C), 70% ethanol and a commercial product based on isopropyl alcohol for 5, 10, 15 and 30 min. After 30min exposure, on PP the reductions ranged from 3.2 to 4.2 log CFU/cm2 for UV-C, from 2.6 to 3.0 log CFU/cm2 for hot air, from 1.6 to 3.2 log CFU/cm2 for 70% ethanol and from 1.5 to 1.9 log CFU/cm2 for the commercial product. On SS, after the same exposure time, reductions of 1.3-2.2 log CFU/cm2, 2.2 to 3.3 log CFU/cm2, 1.7 to 2.0 log CFU/cm2 and 1.6 to 2.4 log CFU/cm2 were observed for UV-C, hot air, 70% ethanol and commercial product, respectively. UV-C was the only treatment affected by the surface material (p < 0.05) whereas the biofilm age influenced the effectiveness of UV-C and hot air (p < 0.05). For most treatment, there was significant difference among the exposure times (p < 0.05). Overall, the fastest loss in the biofilm viability was noted in the first 5 min, followed by a tail phase. The time predicted by the Weibull model for the first decimal reduction ranged from 0.04 to 9.9 min on PP and from 0.7 to 8.5 min on SS. In addition, the Weibull model indicates that most of treatments (79%) required a long-term exposure time (>30 min) to achieve 3-log reductions of Salmonella biofilms. In summary, UV-C showed the best performance on PP whereas hot air was noted to be the most effective on SS.

Biofilm formation and resistance to sanitizers by Salmonella spp. Isolated from the peanut supply chain.

Pathogens such as Salmonella can be difficult to control in low-moisture food (LMF) processing plants and because of this its presence especially in biofilm mode should be prevented in such an environment. This study evaluated the capacity of Salmonellastrains isolated from the peanut supply chain (S. Muenster, S. Miami, S. Glostrup, S. Javiana, S. Oranienburg and S. Yoruba) to form biofilm as well as their resistance to sanitizers (sodium hypochlorite, peracetic acid, quaternary ammonium, alkaline chlorinated solution and biguanide). Regarding biofilm formation, there was no significant difference (p > 0.05) among the strains tested singly on AISI 304 stainless steel (SS) and polypropylene (PP) coupons at the same temperature. However, a difference (p < 0.05) between the temperatures was noted in the first hours of incubation. The sessile cells reached counts between 3 and 4 log CFU/cm2 at 25 °C whereas>5 log CFU/cm2 was observed at 37 °C after 8 h. From 24 h the counts were above 6 log CFU/cm2 for both temperatures. Nevertheless, the SEM images of the 6-strain pool showed the highest density of adhered cells after 48 h at 25 °C and 24 h at 37 °C on PP, and after 48 h at both temperatures on SS. Peracetic acid (300 mg/L) had the shortest action time against 24-h biofilm on SS and PP, with sessile cell counts below the limit of detection (0.59 log CFU/cm2) after 3 min. For 48-h and 96-h biofilm, sodium hypochlorite (200 mg/L) decreased>4 log CFU/cm2 within 5 min. Quaternary ammonium (350 mg/L) and chlorinated alkaline detergent (200 mg/L) showed intermediate performances. Only biguanide (800 mg/L) did not reduce the biofilm counts to below the limit of detection in any of the conditions evaluated. The results indicated high biofilm formation ability of the Salmonella strains isolated from the peanut supply chain. Nevertheless, in general the biofilms were sensitive to most sanitizers within 15 min of treatment. This was the first study which evaluated biofilm formation by Salmonella isolated from the peanut supply chain. Data obtained here will contribute to optimize the hygiene practices in LMF manufacturing plants.