Effects of water, sodium hypochlorite, peroxyacetic acid, and acidified sodium chlorite on in-shell hazelnuts inoculated with Salmonella enterica serovar Panama.

Recent foodborne disease outbreaks involving minimally processed tree nuts have generated a need for improved sanitation procedures. Chemical sprays and dips have shown promise for reducing pathogens on fresh produce, but little research has been conducted for in-shell hazelnuts. This study analyzed the effectiveness of 3 chemical sanitizers for reducing Salmonella on in-shell hazelnuts. Treatments of water, sodium hypochlorite (NaOCl; 25 and 50 ppm), peroxyacetic acid (PAA; 80 and 120 ppm), and acidified sodium chlorite (ASC; 450, 830, and 1013 ppm) were sprayed onto hazelnut samples inoculated with Salmonella enterica serovar Panama. Hazelnut samples were immersed in liquid cultures of S. Panama for 24 h, air-dried, and then sprayed with water and chemical treatments. Inoculation achieved S. Panama populations of approximately 8.04 log CFU/hazelnut. Surviving S. panama populations were evaluated using a nonselective medium (tryptic soy agar), incubated 3 h, and then overlaid with selective media (xylose lysine deoxycholate agar). All of the chemical treatments significantly reduced S. Panama populations (P ≤ 0.0001). The most effective concentrations of ASC, PAA, and NaOCl treatments reduced populations by 2.65, 1.46, and 0.66 log units, respectively. ASC showed the greatest potential for use as a postharvest sanitation treatment.

Investigation of the presence of OH radicals in electrolyzed NaCl solution by electron spin resonance spectroscopy.

In the anode side of a two-chamber electrolyzer, electrolysis of a NaCl solution generates acidic electrolyzed oxidizing (EO) water, which exhibits bactericidal effects against a large number of pathogens. This study was undertaken to investigate whether OH radical species are present in EO water or are formed when EO water reacts with iron ions. Electron spin resonance spectroscopy (ESR) coupled with the spin trapping technique was used for the detection of free radicals. Samples of EO water were collected at 0.5, 1, 2, 3, and 5 min of electrolysis and immediately mixed with the spin trapping agent 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). The 5,5-dimethyl-2-hydroxypyrrolidine-N-oxyl (DMPO-OH) spin adduct, characteristic of OH radicals, was not observed. Starting with 2-min electrolysis, a seven-line spectrum characteristic of 5,5-dimethyl-2-pyrrolidone-N-oxyl (DMPOX) was formed. The reactions of EO water with Fe3+ and Fe2+ in the presence of DMPO yielded the spin adduct DMPO-OH. However, the addition of OH radical scavengers (ethanol and methanol) did not generate the characteristic DMPO-alkyl spin adducts. This indicated that the DMPO-OH spectrum was due to a nucleophilic addition of water to DMPO and not to trapping of OH radicals.

5,5-Dimethyl-2-pyrrolidone-N-oxyl formation in electron spin resonance studies of electrolyzed NaCl solution using 5,5-dimethyl-1-pyrroline-N-oxide as a spin trapping agent.

Electrolyzed oxidizing (EO) water has recently generated much interest as a disinfectant in the food industry. 5,5-Dimethyl-1-pyrroline-N-oxide (DMPO) is a spin trapping agent widely used in the electron spin resonance (ESR) characterization of oxygen-centered free radicals. The reaction between electrolyzed water, collected from the anode side of a two-chamber electrolyzer, and DMPO was investigated by ESR spectroscopy. Addition of DMPO to EO water generated an ESR spectrum identical to that of 5,5-dimethyl-2-pyrrolidone-N-oxyl (DMPOX), suggesting that a compound from EO water oxidized DMPO with the formation of DMPOX. To further investigate the electrolytically generated compound that oxidized DMPO, aqueous solutions of different sodium salts (sodium chloride, sodium citrate, and sodium iodide) with similar conductivities were electrolyzed. The DMPOX signal was not detected in the electrolyzed sodium citrate sample, suggesting that DMPOX formation in the electrolyzed NaCl sample might be due to an electrolytically generated chlorine species. A low DMPOX signal was also observed from the electrolyzed NaI sample, suggesting that a similar species obtained through the electrolysis of I- can also oxidize DMPO. Hypochlorous acid is proposed to oxidize the spin trap DMPO with the formation of DMPOX. In a neutral pH environment, electrolyzed water also oxidized DMPO to DMPOX. This is consistent with the DMPOX formation in the reaction of chlorine water (containing HOCl and Cl2) or sodium hypochlorite with DMPO.

Reduction of Salmonella enterica on alfalfa seeds with acidic electrolyzed oxidizing water and enhanced uptake of acidic electrolyzed oxidizing water into seeds by gas exchange.

Alfalfa sprouts have been implicated in several salmonellosis outbreaks in recent years. The disinfectant effects of acidic electrolyzed oxidizing (EO) water against Salmonella enterica both in an aqueous system and on artificially contaminated alfalfa seeds were determined. The optimum ratio of seeds to EO water was determined in order to maximize the antimicrobial effect of EO water. Seeds were combined with EO water at ratios (wt/vol) of 1:4, 1:10, 1:20, 1:40, and 1:100, and the characteristics of EO water (pH, oxidation reduction potential [ORP], and free chlorine concentration) were determined. When the ratio of seeds to EO water was increased from 1:4 to 1:100, the pH decreased from 3.82 to 2.63, while the ORP increased from +455 to +1,073 mV. EO water (with a pH of 2.54 to 2.38 and an ORP of +1,083 to +1,092 mV) exhibited strong potential for the inactivation of S. enterica in an aqueous system (producing a reduction of at least 6.6 log CFU/ml). Treatment of artificially contaminated alfalfa seeds with EO water at a seed-to-EO water ratio of 1:100 for 15 and 60 min significantly reduced Salmonella populations by 2.04 and 1.96 log CFU/g, respectively (P < 0.05), while a Butterfield's buffer wash decreased Salmonella populations by 0.18 and 0.23 log CFU/g, respectively. After treatment, EO water was Salmonella negative by enrichment with or without neutralization. Germination of seeds was not significantly affected (P > 0.05) by treatment for up to 60 min in electrolyzed water. The uptake of liquid into the seeds was influenced by the internal gas composition (air, N2, or O2) of seeds before the liquid was added.

Plantaricin W from Lactobacillus plantarum belongs to a new family of two-peptide lantibiotics.

Plantaricin W (Plw) is a new two-peptide bacteriocin, from Lactobacillus plantarum, which inhibits a large number of Gram-positive bacteria. The two peptides, Plwalpha (comprising 29 residues) and Plwbeta (comprising 32 residues), were isolated from the culture supernatants and characterized. The individual peptides had low antimicrobial activity but acted synergistically, and synergism was seen at all mixing ratios tested. The data indicate that the two peptides work in a 1:1 ratio. Chemical analyses showed that both peptides are lantibiotics, but two unmodified cysteines and one serine residue were present in Plwalpha, and Plwbeta contained one cysteine residue. The Plw structural genes were sequenced and shown to encode prepeptides with sequence similarities to two other two-peptide lantibiotics, namely staphylococcin C55 and lacticin 3147. The conserved residues are mainly serines, threonines and cysteines that can be involved in intramolecular thioether bond formation in the C-terminal parts of the molecules. This indicates that these bacteriocins are members of a new family of lantibiotics with common bridging patterns, and that the ring structures play an important functional role. Based on the data a structural model is presented in which each peptide has a central lanthionine and two overlapping thioether bridges close to their C-termini.

Correlation of Cellular Phospholipid Content with Nisin Resistance of Listeria monocytogenes Scott A.

A nisin-resistant mutant of Listeria monocytogenes Scott A has been characterized by comparing its phospholipid composition with the nisin-sensitive parental strain. The total phospholipids of resistant cells were significantly (P < 0.001) decreased compared to the parental strain. The types of phospholipids isolated from nisin-resistant and sensitive cells were identical, but there was a significant decrease (P < 0.01) in the amount of three individual phospholipids. Nisin-resistant cells were found to bind less nisin and release less phospholipids than sensitive cells when treated with same concentrations of nisin. The cell surface of resistant cells was less hydrophobic compared to sensitive cells, which also may have contributed to the observed nisin resistance. The results suggest that fundamental changes occurred in the membrane structure and function of the resistant mutant as a response to nisin.

Nisin Resistance of Foodborne Bacteria and the Specific Resistance Responses of Listeria monocytogenes Scott A.

Eight foodborne pathogenic and spoilage type gram-positive bacteria were evaluated for their spontaneous resistance frequencies to the peptide antimicrobial nisin. In brain heart infusion medium, spontaneous nisin resistance frequencies were in the range of 10-6 to 10-8 when exposed to nisin at concentrations 2 to 8 times the minimal inhibitory concentrations. A resistant mutant of Listeria monocytogenes Scott A (2000 U nisin per ml) was obtained by increasing stepwise exposure to nisin and was subsequently characterized. Nisin was not inactivated after exposure to mutant or parent cells growing in brain heart medium. Membrane fatty acid composition, phase transition temperature profiles (by differential scanning calorimetry), and specific growth rates of the resistant mutant and parent strain were compared. The resistant mutant had a higher phase transition temperature, higher percentage of straight-chain fatty acids, and a lower percentage of branched chain-fatty acids. The specific growth rate (k) of the resistant mutant was significantly decreased at the suboptimal temperature of 20°C where (k) was 40.9% of the parent strain k. In contrast, at 37°C, the mutant (k) was 87.6% of the parent (k). Collectively, these observations indicated that as a resistance response to nisin, fundamental changes occurred in bacterial membrane structure and function as opposed to a resistance response involving nisin degradation.

Antimicrobial Activity of Nisin Adsorbed to Hydrophilic and Hydrophobic Silicon Surfaces.

The antimicrobial activity of nisin was studied after its adsorption to hydrophilic and hydrophobic silicon surfaces. Adsorption was allowed to occur from buffered nisin solutions under static conditions, and the adsorbed mass of nisin was calculated from the resultant film thickness and refractive index, determined using ellipsometry. Once adsorbed, nisin was observed to be stable to buffer rinsing; the amount of nisin adsorbed onto each type of surface was determined to be of a quantity sufficent for inhibition of susceptible bacteria. Antimicrobial activity was maintained both upon silicon surface contact with microbial media and after nisin desorption induced by surfactant displacement.