Effects of high pressure argon treatments on the quality of fresh-cut apples at cold storage

High pressure (HP) argon (Ar) processing that makes argon and water molecules form clathrate hydrates to restrict intracellular water activity and enzymatic reactions. This can be used in the preservation of fruits and vegetables. Effects of HP (150 MPa) Ar treatments on preserving fresh-cut apples were investigated at 4 °C for two weeks. Respiration rate and ethylene production of fresh-cut apples treated by the HP (150 MPa) Ar for 10 min were lower apparently in comparison with those untreated and treated by flushing with Ar and the HP air for 10 min. The HP Ar treatment delayed browning and microbial growth of fresh-cut apples at cold storage, because the populations of both mesophiles and psychrotrophs did not exceed 6.0 log cfu/g, and those for molds and yeasts were less than 3.0 log cfu/g after two weeks storage. HP Ar treatment did not affect the content of titrated acidity and soluble solids, and significantly reduced the total phenolics decrease in fresh-cut apples (p < 0.05). Dipping into chemical solution, such as 0.5% ascorbic acid (AA), 0.5% citric acid (CA) and 0.5% calcium chloride (CC) for 5 min could reduce the changes in the color and firmness of apple wedges during HP operation, and the combined HP Ar with dipping treatment remained good sensory attributes of fresh-cut apples for 12 days at 4 °C. These results indicated the HP Ar treatment could be an effective method for improving the quality of fresh-cut apples at cold storage conditions.     

Combined effect of acidic electrolyzed water (AcEW) and alkaline electrolyzed water (AlEW) on the microbial reduction of fresh-cut cilantro

In the present study, the disinfection efficacy on fresh-cut cilantro of the combination of strongly acidic electrolyzed water (AcEW) and alkaline electrolyzed water (AlEW) was evaluated, in comparison with single slightly acidic electrolyzed water (SAEW) and single AcEW treatments. The populations of E. Coli O78 on inoculated cilantro treated by AlEW 5 min + AcEW 5 min, was not detected while 3.43 and 3.73 log₁₀ CFU/g in the AlEW 2.5 min + AcEW 2.5 min and AcEW 2 min + AlEW 2 min + AcEW 2 min treatments respectively. Our results implied that the bactericidal abilities of the combination of AlEW and AcEW treatments were higher than that of single AcEW and SAEW, which also was demonstrated microscopically by scanning electron microscopy (SEM). Moreover, the efficacy of combination of AcEW and AlEW in reducing natural micro flora on fresh-cut cilantro was also evaluated compared with single AcEW and SAEW. The results showed that the combination of AlEW and AcEW had stronger sterilization ability than single AcEW and SAEW. Considering the utilizations of AlEW and disinfection efficacy, we suggest that the combination of AlEW and AcEW may also be a better choice in fresh-cut produce.     

Combined sustainable sanitising treatments to reduce Escherichia coli and Salmonella Enteritidis growth on fresh-cut kailan-hybrid broccoli

The effects of peroxyacetic acid (PA), neutral electrolysed water (NEW), ultraviolet C light (UV-C) and superatmospheric O₂ packaging (HO), single or combined, on the growth rate of Escherichia coli and S. Enteritidis inoculated onto fresh-cut kailan-hybrid broccoli were studied throughout 14 days of shelf life at 5 and 10 °C. As controls, unwashed, water-washed and NaClO-washed were used. PA and NEW showed a better sanitising effect than NaClO against both E. coli/S. Enteritidis with reductions of 2.2/2.7 and 2.6/2.6 log CFU g⁻¹, respectively. UV-C attained E. coli/S. Enteritidis decreases of 1.3–1.4/2.1–2.2 log CFU g⁻¹ compared to unwashed samples. The bacteriostatic effects of PA or NEW were improved when they were combined with UV-C, decreasing E. coli and S. Enteritidis counts by about 3 log CFU g⁻¹. After 14 days, PA and NEW-treated samples attained E. coli/S. Enteritidis reductions at 5 °C of 2.3/1.4 and about 1 log CFU g⁻¹, respectively. Storage of those samples at 10 °C masked that sanitising effect. At both storage temperatures, UV-C-treated samples registered lower E. coli and S. Enteritidis reductions (or higher increases for S. Enteritidis at 10 °C) regarding conventional NaClO-sanitized samples or other single treatments. However, PA, NEW or UV-C-treated samples under HO at both storage temperatures showed better bacterial control than individual treatments with the greatest effectiveness for UV-C + HO. Triple combination did not imply an enhanced benefit over double combinations. Conclusively, PA, NEW and UV-C seems to be effective emergent alternatives to NaClO to reduce initial E. coli and S. Enteritidis populations in fresh-cut kailan-hybrid broccoli. Storage at 5 or 10 °C under HO greatly controlled microbial growth.     

Modelling survival behaviour of Salmonella enterica ser. Enteritidis,Typhimurium and Tennessee on table eggs during storage at different temperatures

Quantitative risk assessment studies on the health risk of Salmonella due to consumption of contaminated table eggs are based on the assumption that Salmonella is inside the egg and that the pathogen belongs to serovar Enteritidis. However different serovars of Salmonella may contaminate the surface of table eggs and spread to other foods at consumer's kitchen due to improper food handling. In the present study the survival behaviour of one strain each from Salmonella enterica serovars Enteritidis, Typhimurium and Tennessee on table egg surface during storage at 4, 8, and 20 °C have been described. Besides, in those cases observed data were subjected for modelling; linear, log-linear tail and Weibull models were compared in terms of model fitting and model performance. Overall, in most cases, inactivation kinetics presented a linear trend on Salmonella behaviour so that Weibull and linear models adequately described observed data. Regarding log-linear tail models, though they presented a better fitting, their adequacy could not be assessed given the lack of data in the tail region. Regarding storage temperatures, 4 °C was predicted to be the most inhibitory temperature for table eggs externally contaminated by a strain of S. enterica serovar Enteritidis. After 28 days of storage, a reduction of 4 log₁₀ cfu/g of eggshell on the S. enterica ser. Enteritidis load was registered at 4 °C. S. enterica ser. Typhimurium and Tennessee showed higher survival rates at all tested temperatures. The results highlighted the importance of keeping constant the storage temperature of table eggs in order to reduce the risk of S. enterica ser. Enteritidis contaminating the surface of table eggs. However this temperature might not be the optimal one in view of S. enterica serovars other than Enteritidis.     

Reduction of Escherichia coli O157, Listeria monocytogenes and Salmonella enterica sv. Typhimurium populations on fresh-cut bell pepper using gaseous ozone

Bacterial contamination is the main cause of food poisoning which can lead to diarrhoea, abdominal cramp, vomiting as well as death. Bacterial contamination can potentially be controlled by application of gaseous ozone due to its antibacterial activity. Therefore, the objective of this study was to investigate the efficacy of gaseous ozone for reducing food-borne pathogens such as Escherichia coli O157, Listeria monocytogenes and Salmonella enterica sv. Typhimurium on fresh-cut bell pepper. Efficacy of gaseous ozone to reduce bacterial populations was investigated in vitro and in vivo. Results showed that optimum effect of ozone on reducing bacterial populations was achieved with short term exposures of less than 6 h. Ozone reduced the bacterial population by disrupting bacterial cell structure, which lead to cellular death. Results also showed that bacterial cells have different resistance to ozone where ozone was more effective against L. monocytogenes, followed by E. coli O157 and Salmonella Typhimurium. Optimal reduction of the bacterial population on fresh-cut bell pepper was achieved with exposure to 9 ppm ozone for 6 h. This treatment reduced 2.89, 2.56 and 3.06 log of E. coli O157, Salmonella Typhimurium and L. monocytogenes populations, respectively. In conclusion, exposure to 9 ppm ozone for 6 h helps in reducing food-borne pathogen on fresh-cut bell pepper and has high potential to be an alternative sanitization treatment to reduce pathogen population on fruit.     

Assessing biofilm formation by Salmonella enterica serovar Typhimurium on abiotic substrata in the presence of quorum sensing signals produced by Hafnia alvei

This study aimed to evaluate the possible impact of N-acyl-homoserine lactones (AHLs) produced by Hafnia alvei on the biofilm-forming ability of Salmonella enterica ser. Typhimurium. To do this, S. Typhimurium was left to form biofilms on two abiotic substrata, stainless steel (SS) and polystyrene (PS), through their static incubation for up to 48 h, at 20 °C, in laboratory growth media, also containing crude or ethyl acetate extracted cell-free culture supernatant of either the AHL-producing H. alvei 718 strain or its AHL-lacking isogenic mutant. Apart from the presence of signals, two nutritional conditions, a rich and a poor one, were also evaluated in those experiments involving the ethyl acetate extracted supernatants. The presence of AHLs in all media was tested using Agrobacterium tumefaciens biosensor-based bioassay, while the quantities of biofilms formed were in parallel estimated through three different quantification methods, namely agar plating, conductance, and absorbance measurements. Results revealed a significant correlation in biofilm formation among both tested surfaces, with the conductance detection times to be also inversely well correlated to the biofilm counts on SS. Interestingly, S. Typhimurium in general presented a higher capability to form biofilms under the nutrient poor compared to rich conditions. However, all hereby employed biofilm setup and quantification methods did not reveal any significant influence of H. alvei AHLs on Salmonella biofilm-forming behavior. In agreement, further experiments conducted using a synthetic AHL (i.e.3OC6-HSL), simulating a major such signal produced by H. alvei, did not show any effect. To sum up, these results expand our knowledge on the potential role of interspecies signaling on biofilm formation by S. Typhimurium.     

Influence of the hydrophobicity and surface roughness of mangoes and tomatoes on the adhesion of Salmonella enterica serovar Typhimurium and evaluation of cleaning procedures using surfactin

Salmonellosis is associated with the consumption of raw vegetables and fruits such as tomatoes, watermelons, alfalfa sprouts, radishes, carrots, lettuce and parsley. The influence of the fruits' roughness on bacterial adhesion was evaluated as measured using a profilometer. The adhesion of Salmonella enterica serovar Typhimurium to mango and tomato surfaces was also evaluated by measuring of the hydrophobicity of the microorganisms and the fruits surfaces. The bacteria adherent on fruit's surface was quantified by plate count and visualize by scanning electron microscopy. In addition, the efficiency of surfactin in removing S. Typhimurium from the fruits' surfaces was analyzed. The average roughness (R_a) of mango (4.54 ± 1.95 μm) was significantly different (p < 0.05) compared to tomato (2.88 ± 2.15 μm). The adhesion of the microorganisms to the fruits' surfaces, as predicted by a determination of the total energy of adhesion (ΔG), was thermodynamically unfavorable. Despite these data, the numbers of bacteria on both fruits' surfaces were similar (p > 0.05), reaching 5.95 ± 0.36 log CFU cm⁻² and 5.81 ± 0.39 log CFU cm⁻² on mango and tomato, respectively. Therefore, these results suggest that the adhesion observed in this experiment is a multifactorial process. Surfactin removed 94.3% and 92.2% of the S. Typhimurium adhered to the surfaces of the mangoes and tomatoes, respectively. Our research showed that the roughness and hydrophobicity of the fruits' surface did not affect the efficiency of each sanitation treatments on removing of S. Typhimurium. It was observed that the chlorine was more efficient treatment (p < 0.05) for tomato surface. For surface of mangoes, chorine and surfactin were better than water treatment for bacteria control.