Control of Listeriamonocytogenes on commercially-produced frankfurters prepared with and without potassium lactate and sodium diacetate and surface treated with lauric arginate using the Sprayed Lethality in Container (SLIC®) delivery method

Viability of Listeriamonocytogenes was monitored on frankfurters formulated with or without potassium lactate and sodium diacetate at a ratio of ca. 7:1 and treated with lauric arginate (LAE; 22 or 44 ppm) using the Sprayed Lethality in Container (SLIC®) delivery method. Without antimicrobials, pathogen numbers remained relatively constant at ca. 3.3 log CFU/package for ca. 30 d, but then increased to ca. 8.4 log CFU/package over 120 d. Regardless of whether or not lactate and diacetate were included, when treated with LAE, pathogen numbers decreased from ca. 3.3 log CFU/package to ca. 1.5 log CFU/package within 2 h, but then increased to 7.3 and 6.7 log CFU/package, respectively, after 120 d. When frankfurters were formulated with lactate and diacetate and treated with LAE, pathogen numbers decreased by ca. 2.0 log CFU/package within 2 h and remained relatively unchanged over the 120 d. These data confirm that LAE provides an initial lethality towards L. monocytogenes and when used in combination with reduced levels/ratio of lactate and diacetate as an ingredient for frankfurters provides inhibition throughout shelf life.     

Inactivation of Escherichia coli O157:H7 and Salmonella spp. on alfalfa seeds by caprylic acid and monocaprylin

Alfalfa and other seed sprouts have been implicated in several Escherichia coli O157:H7 and Salmonella spp. human illness outbreaks in the U.S. Continuing food safety issues with alfalfa seeds necessitate the need for discovery and use of novel and effective antimicrobials. The potential use of caprylic acid (CA) and monocaprylin (MC) for reducing E. coli O157:H7 and Salmonella spp. populations on alfalfa seeds was evaluated. The effectiveness of three concentrations of CA and MC (25, 50, and 75 mM) to reduce E. coli O157:H7 and Salmonella spp. populations in 0.1% peptone water and on alfalfa seeds was evaluated. Surviving populations of E. coli O157:H7 and Salmonella spp. were enumerated by direct plating on tryptic soy agar (TSA). Non-inoculated alfalfa seeds were soaked for up to 120 min to evaluate the effect of CA and MC solutions on seed germination rate. For planktonic cells, the efficacy of the treatments was: 75 MC > 50 MC > 25 MC > 75 CA > 50 CA > 25 CA. Both E. coli O157:H7 and Salmonella spp. were reduced to below the detection limit (0.6 log CFU/ml) within 10 min of exposure to 75 MC from initial populations of 7.65 ± 0.10 log CFU/ml and 7.71 ± 0.11 log CFU/ml, respectively. Maximum reductions of 1.56 ± 0.25 and 2.56 ± 0.17 log CFU/g for E. coli O157:H7 and Salmonella spp., respectively, were achieved on inoculated alfalfa seeds (from initial populations of 4.74 ± 0.62 log CFU/g and 5.27 ± 0.20 log CFU/g, respectively) when treated with 75 MC for 90 min. Germination rates of CA or MC treated seeds ranged from 84% to 99%. The germination rates of CA or MC soaked seeds and water soaked seeds (control) were similar (P > 0.05) for soaking times of ≤ 90 min. Monocaprylin (75 mM) can be used to reduce E. coli O157:H7 and Salmonella spp. on alfalfa seeds without compromising seed viability.     

Salmonella surveillance and control at post-harvest in the Belgian pork meat chain

Salmonella remains the primary cause of reported bacterial food borne disease outbreaks in Belgium. Pork and pork products are recognized as one of the major sources of human salmonellosis. In contrast with the primary production and slaughterhouse phases of the pork meat production chain, only a few studies have focussed on the post-harvest stages. The goal of this study was to evaluate Salmonella and Escherichia coli contamination at the Belgian post-harvest stages. E. coli counts were estimated in order to evaluate the levels of faecal contamination. The results of bacteriological analysis from seven cutting plants, four meat-mincing plants and the four largest Belgian retailers were collected from official and self-monitoring controls. The prevalence of Salmonella in the cutting plants and meat-mincing plants ranged from 0% to 50%. The most frequently isolated serotype was Salmonella typhimurium. The prevalence in minced meat at retail level ranged from 0.3% to 4.3%. The levels of Salmonella contamination estimated from semi-quantitative analysis of data relating to carcasses, cuts of meat and minced meat were equal to −3.40 ± 2.04 log CFU/cm², −2.64 ± 1.76 log CFU/g and −2.35 ± 1.09 log CFU/g, respectively. The E. coli results in meat cuts and minced meat ranged from 0.21 ± 0.50 to 1.23 ± 0.89 log CFU/g and from 1.33 ± 0.58 to 2.78 ± 0.43 log CFU/g, respectively. The results showed that faecal contamination still needs to be reduced, especially in specific individual plants.     

Inactivation of Escherichia coli O157:H7 on stainless steel upon exposure to Paenibacillus polymyxa biofilms

We investigated the potential use of biofilm formed by a competitive-exclusion (CE) microorganism to inactivate Escherichia coli O157:H7 on a stainless steel surface. Five microorganisms showing inhibitory activities against E. coli O157:H7 were isolated from vegetable seeds and sprouts. The microorganism with the greatest antimicrobial activity was identified as Paenibacillus polymyxa (strain T5). In tryptic soy broth (TSB), strain T5 reached a higher population at 25 °C than at 12 or 37 °C without losing inhibitory activity against E. coli O157:H7. When P. polymyxa (6 log CFU/mL) was co-cultured with E. coli O157:H7 (2, 3, 4, or 5 log CFU/mL) in TSB at 25 °C, the number of E. coli O157:H7 decreased significantly within 24 h. P. polymyxa formed a biofilm on stainless steel coupons (SSCs) in TSB at 25 °C within 24 h, and cells in biofilms, compared to attached cells without biofilm formation, showed significantly increased resistance to a dry environment (43% relative humidity [RH]). With the exception of an inoculum of 4 log CFU/coupon at 100% RH, upon exposure to biofilm formed by P. polymyxa on SSCs, populations of E. coli O157:H7 (2, 4, or 6 log CFU/coupon) were significantly reduced within 48 h. Most notably, when E. coli O157:H7 at 2 log CFU/coupon was applied to SSCs on which P. polymyxa biofilm had formed, it was inactivated within 1 h, regardless of RH. These results will be useful when developing strategies using biofilms produced by competitive exclusion microorganisms to inactivate foodborne pathogens in food processing environments.     

Effects of some commercial additives on the quality of sucuk (Turkish dry-fermented sausage)

The effects of some commercial additives on the quality of sucuk (Turkish dry-fermented sausage) were investigated during the ripening and storage periods. Microbial, chemical and sensory changes were followed for 15 days of ripening and 36 days of storage. Aerobic plate count (APC) increased (P < 0.05) from 5.19 to 6.09 log CFU/g during the first 10 days of ripening and afterwards decreased (P < 0.05) to 3.69 log CFU/g. APC and lactic acid bacteria (LAB) changed significantly (P < 0.05) with time and additives. LAB increased (P < 0.05) from 4.62 log CFU/g to about 5.47 log CFU/g during the first 10 days of the ripening period and decreased to 1.79 log CFU/g at the end of storage. Control sucuk without additives had the highest level of mould and yeast counts (5.09 log CFU/g). TBARS values increased gradually (P < 0.05) from 0.61 to 1.73 mg/kg and tyramine concentrations varied from 56.8 to 419 mg/kg. Control sucuk was found to have the lowest overall sensory quality (P < 0.05), and nitrate/nitrite concentration increased (P < 0.05) the overall sensory quality of the sausages. Pearson’s correlation test indicated that there was a link (P < 0.01) between the overall sensory quality and pH, TBARS values, mould and yeast counts, and putrescine concentration.     

Effect of lactoferrin and its derivatives against gram-positive bacteria in vitro and, combined with high pressure, in chicken breast fillets

The bactericidal activity of lactoferrin (LF), amidated lactoferrin (AMILF), pepsin digested lactoferrin (PDLF), and its activated (ALF) commercial form, against six strains of three gram-positive bacterial species was investigated. Listeria monocytogenes was most sensitive in vitro, Staphylococcus aureus showed a moderate resistance, and Enterococus faecalis was highly resistant to antimicrobials. When chicken breast fillets were inoculated with L. monocytogenes CECT5725 and treated with antimicrobials, reductions were below 0.5 log CFU/ml in all cases. In combination with high pressure (HHP) treatment at 400 MPa for 10 min, antimicrobials showed a slight additional bactericidal effect, always below 1 log CFU/g. Incorporation of antimicrobials 18 h before or 1 h after HHP treatment generally yielded better results than incorporation 1 h before HHP treatment, although reductions remained below 1.5 log CFU/g in all cases. LF and its derivatives showed a limited potential for pathogen control in meat.     

Efficacies of soy sauce and wine base marinades for controlling spoilage of raw beef

Fresh beef slices were marinated by immersion in marinades based on soy sauce without (SB) or with lactic acid (SBLA) or red wine base without (WB) or with 0.5% v/v oregano essential oil (WBO). For control samples (immersed in saline), a mean increase of 0.9log CFU/cm² in total viable counts (TVCs) occurred during the 24 h treatment. During marination with WB and SB, mean TVC decreased by 0.7 and 0.3log CFU/cm², respectively. The mean decrease in TVC for samples marinated in WBO or SBLA was 1.2log CFU/cm². Subsequent storage of beef resulted in a rapid increase of TVC in control samples, to ≥9.5log CFU/cm² after 8 days at 5 °C or 3 days at 15 °C. Significant (P < 0.05) microbial growth occurred in marinated samples stored at 5 °C. During storage at 15 °C TVC increased in only WB samples but the final numbers of 5.9log CFU/cm² were significantly lower (P < 0.05) than the numbers in the control. Results similar to those for TVC were observed for Pseudomonas spp. All marinades also gave meat with significant lower TBARS values than the controls. There were no significant differences (P > 0.05) in the toughness of the marinated samples compared to the control, except for SBLA samples which had significantly higher (P < 0.05) shear force values. Marination with soy sauce or red wine marinades can evidently control microbial spoilage and oxidation of meat.     

Fate of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella on fresh-cut celery

Illnesses from Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella have been associated with the consumption of numerous produce items. Little is known about the effect of consumer handling practices on the fate of these pathogens on celery. The objective of this study was to determine pathogen behavior at different temperatures under different storage conditions. Commercial fresh-cut celery was inoculated at ca. 3 log CFU/g onto either freshly cut or outer uncut surfaces and stored in either sealed polyethylene bags or closed containers. Samples were enumerated following storage for 0, 1, 3, 5, and 7 days when held at 4 °C or 12 °C, and after 0, 8, and 17 h, and 1, and 2 days when held at 22 °C. At 4 °C, all populations declined by 0.5–1.0 log CFU/g over 7 days. At 12 °C, E. coli O157:H7 and Salmonella populations did not change, while L. monocytogenes populations increased by ca. 0.5 log CFU/g over 7 days. At 22 °C, E. coli O157:H7, Salmonella, and L. monocytogenes populations increased by ca. 1, 2, or 0.3 log CFU/g, respectively, with the majority of growth occurring during the first 17 h. On occasion, populations on cut surfaces were significantly higher than those on uncut surfaces. Results indicate that populations are reduced under refrigeration, but survive and may grow at elevated temperatures.     

Characterisation and stability evaluation of bixin nanocapsules

The aim of this study was to produce bixin nanocapsules by the interfacial deposition of preformed poly-?-caprolactone (PCL). PCL (250 mg), capric/caprylic triglyceride (400 μL), sorbitan monostearate (95 mg) and bixin were dissolved in a mixture of acetone (60 mL) and ethanol (7.5 mL) under stirring (40 °C). This organic solution was added to the aqueous solution (130 mL) containing Tween 80 (195 mg). The size distributions in the formulations with bixin concentration from 11 to 100 μg/mL were evaluated periodically during 3 weeks of storage at ambient temperature. The optimal formulation (bixin concentration of 16.92 ± 0.16 μg/mL) was characterised in terms of particle size distribution, zeta potential, bixin content and encapsulation efficiency, and showed a volume-weighted mean diameter (D_4,3) of 195 ± 27 nm, around 100% of encapsulation efficiency and the nanocapsules were considered physically stable during 119 days of storage at ambient temperature.     

Histamine formation by histamine-forming bacteria in douchi,a Chinese traditional fermented soybean product

Seven soybean and 19 black bean douchi products sold in the supermarkets in southern Taiwan were purchased and tested to determine the occurrence of histamine and histamine-forming bacteria. The levels of pH, salt content, water content, yeast and mold, and aerobic plate count (APC) in all samples ranged from 4.7 to 5.9, 4.4% to 14.0%, 6.8% to 51.6%, 3.0 to 5.1 log CFU/g, and 5.2 to 9.2 log CFU/g, respectively. None of these samples contained total coliform and Escherichia coli. Although black bean douchi products had an average histamine content of 29.0 mg/100 g, 18 of them had histamine contents greater than 5 mg/100 g, the allowable level set by the US Food and Drug Administration (FDA) for scombroid fish and/or products. In contrast, only four soybean douchi products had histamine levels greater than 5 mg/100 g. Among the black bean samples, four contained histamine at 56.3, 62.1, 80.2 and 80.8 mg/100 g, that are above the 50 mg/100 g hazard action level. Eight histamine-forming bacterial strains, capable of producing 11.7–601 ppm of histamine in trypticase soy broth (TSB) supplemented with 1% l-histidine (TSBH), were identified as Bacillus subtilis (four strains) Staphylococcus pasteuri (one strain) and Staphylocuccus capitis (three strains) by 16S rDNA sequencing with PCR amplification. S. capitis, which was previously reported to be halotolerant, was a potent histamine-former capable of producing more than 500 ppm of histamine in TSBH in the presence of 0.5–10% NaCl.     

A mathematical model of inactivation kinetics for a four-strain composite of Salmonella Enteritidis and Oranienburg in commercial liquid egg yolk

The goal of this study was to develop a general model of inactivation of salmonellae in commercial liquid egg yolk for temperatures ranging from 58 °C to 66 °C by studying the inactivation kinetics of Salmonella in liquid egg yolk. Heat-resistant salmonellae (three serovars of Enteritidis [two of phage type 8 and one PT 13] and one Oranienburg) were grown to stationary phase in Tryptic Soy Broth and concentrated 10-fold by centrifugation. Each inoculum was added to liquid egg yolk and mixed thoroughly, resulting in a final population of ca. 7 log CFU/ml egg yolk. Inoculated yolk was injected into sterile glass capillary tubes, flame-sealed and heated in a water bath at 58, 60, 62, 64, and 66 °C. Capillary tubes were ethanol sanitized, rinsed, and contents were extracted. Yolk was diluted, surface plated onto Tryptic Soy Agar + 0.1% sodium pyruvate and 50 μg/ml nalidixic acid and incubated at 37 °C for 24 h before colonies were enumerated. Decimal reduction values were calculated from survivor curves with a minimum inactivation of 6 log CFU/ml at each temperature. Survival curves (except for 66 °C) featured initial lag periods before first order linear inactivation. Estimated asymptotic D-values were 1.83 min at 58 °C, 0.69 min at 60 °C, 0.26 min at 62 °C, 0.096 min at 64 °C and 0.036 min at 66 °C. The estimate of the asymptotic z-value was ca. 4.7 °C with standard error of 0.07 °C. A linear relationship between the log₁₀ of the lag times and temperature was observed. A general kinetic model of inactivation was developed. The results of the study provide information that can be used by processors to aid in producing safe pasteurized egg yolk products and for satisfying pasteurization performance standards and developing industry guidance.     

Encapsulation of probiotic Lactobacillus bulgaricus in alginate–milk microspheres and evaluation of the survival in simulated gastrointestinal conditions

In this paper, a new encapsulation carrier was applied in order to improve the survival of Lactobacillus bulgaricus (L. bulgaricus). L. bulgaricus was encapsulated in alginate–milk microspheres prepared by extrusion method. Around 100% encapsulation yield was achieved. The tolerance of encapsulated L. bulgaricus to adverse environments such as low pH (pH 2.0 and 2.5), high concentration of bile salt (1.0% and 2.0%) and long time storage (1 month), was investigated. Release characteristic of encapsulated L. bulgaricus in Simulated Intestine Fluid (SIF) was also studied. The results showed that encapsulation could improve the tolerance of L. bulgaricus to adverse environments. The viability of encapsulated L. bulgaricus did not change after 120 min incubation in Simulated Gastric Fluid (SGF) pH 2.5. The viability of encapsulated L. bulgaricus could be kept more than 8 log CFU/g after 120 min incubation in SGF pH 2.0. The viability of encapsulated L. bulgaricus in 1% bile salt solution was reduced from 9.98 log CFU/g microspheres to 9.24 and 8.48 log CFU/g microspheres after 1 and 2 h incubation, respectively. Around 1.3 and 2.1 log CFU/g microspheres were reduced after 1 and 2 h exposure in 2% bile salt solution, respectively. Full viability of encapsulated L. bulgaricus could be preserved after 1 month’s storage at 4 °C. L. bulgaricus encapsulated in alginate–milk microspheres could be completely released in 1 h. These studies demonstrated encapsulation of L. bulgaricus in alginate–milk microspheres is an effective protection technique against extreme simulated gastrointestinal environment.     

Use of low dose e-beam irradiation to reduce E. coli O157:H7, non-O157 (VTEC) E. coli and Salmonella viability on meat surfaces

This study determined the extent that irradiation of fresh beef surfaces with an absorbed dose of 1 kGy electron (e-) beam irradiation might reduce the viability of mixtures of O157 and non-O157 verotoxigenic Escherichia coli (VTEC) and Salmonella. These were grouped together based on similar resistances to irradiation and inoculated on beef surfaces (outside flat and inside round, top and bottom muscle cuts), and then e-beam irradiated. Salmonella serovars were most resistant to 1 kGy treatment, showing a reduction of ≤ 1.9 log CFU/g. This treatment reduced the viability of two groups of non-O157 E. coli mixtures by ≤ 4.5 and ≤ 3.9 log CFU/g. Log reductions of ≤ 4.0 log CFU/g were observed for E. coli O157:H7 cocktails. Since under normal processing conditions the levels of these pathogens on beef carcasses would be lower than the lethality caused by the treatment used, irradiation at 1 kGy would be expected to eliminate the hazard represented by VTEC E. coli.     

Phenolic content and antioxidant capacity of Philippine sweet potato (Ipomoea batatas) varieties

The study established baseline data on the total phenolic content and antioxidant activities of five sweet potato (Ipomoea batatas) varieties grown in the Philippines including Dakol, Emelda, Haponita, PSBSP and Violet. Phenolic content ranged from 192.7 to 1159.0 mg gallic acid equivalent (GAE) /100 g dry sample. Antioxidant activities were highest for Dakol, with an EC₅₀ value of 0.7 ± 0.2 mg/mL for DPPH radical scavenging activity, 2.5 ± 0.5 mg/mL for reducing power, and 2.4 ± 0.3 mg/mL for iron-chelating ability, on a dry basis. However, Haponita had the best inhibitory action on linoleic acid oxidation at 99.4 ± 0.9%. Methanolic sweet potato extracts had higher radical scavenging activity, reducing power and oxidation inhibition than α-tocopherol and higher iron-chelating capacity than ethylenediamine tetraacetic acid (EDTA). Significant (∗P < 0.05) negative correlation was observed between total phenolic content and the EC₅₀ for DPPH radical scavenging activity (R = −0.826), reducing power (R = −0.876) and iron-chelating capacity (R = -0.800).     

Microbial inactivation and shelf life comparison of 'cold' hurdle processing with pulsed electric fields and microfiltration, and conventional thermal pasteurisation in skim milk

Thermal pasteurisation (TP) is the established food technology for commercial processing of milk. However, degradation of valuable nutrients in milk and its sensory characteristics occurs during TP due to substantial heat exposure. Pulsed electric fields (PEF) and microfiltration (MF) both represent emerging food processing technologies allowing gentle milk preservation at lower temperatures and shorter treatment times for similar, or better, microbial inactivation and shelf stability when applied in a hurdle approach compared to TP. Incubated raw milk was used as an inoculum for the enrichment of skim milk with native microorganisms before PEF, MF, and TP processing. Inoculated milk was PEF-processed at electric field strengths between 16 and 42 kV/cm for treatment times from 612 to 2105 μs; accounting for energy densities between 407 and 815 kJ/L, while MF was applied with a transmembrane flux of 660 L/h m². Milk was TP-treated at 75 °C for 24 s. Comparing PEF, MF, and TP for the reduction of the native microbial load in milk led to a 4.6 log₁₀ CFU/mL reduction in count for TP, which was similar to 3.7 log₁₀ CFU/mL obtained by MF (P ≥ 0.05), and more effective than the 2.5 log₁₀ CFU/mL inactivation achieved by PEF inactivation (at 815 kJ/L (P < 0.05)). Combined processing with MF followed by PEF (MF/PEF) produced a 4.1 (at 407 and 632 kJ/L), 4.4 (at 668 kJ/L) and 4.8 (at 815 kJ/L) log₁₀ CFU/mL reduction in count of the milk microorganisms, which was comparable to that of TP (P ≥ 0.05). Reversed processing (PEF/MF) achieved comparable reductions of 4.9, 5.3 and 5.7 log₁₀ CFU/mL (at 407, 632 and 668 kJ/L, respectively (P ≥ 0.05)) and a higher inactivation of 7.1 log₁₀ (at 815 kJ/mL (P < 0.05)) in milk than for TP. Microbial shelf life of PEF/MF-treated (815 kJ/L) and TP-treated milk stored at 4 °C was analysed over 35 days for total aerobic; enterobacteria; yeasts and moulds; lactobacilli; psychrotroph; thermoduric psychrotroph, mesophilic, and thermophilic; and staphylococci counts. For both PEF/MF and TP-treated milk an overall shelf stability of 7 days was observed based on total aerobic counts (P ≥ 0.05). Milk hurdle processing with PEF/MF at its most effective treatment parameters produced greater microbial inactivation and overall similar shelf stability at lower processing temperatures compared to TP. With higher field strength, shorter treatment time, larger energy density, and rising temperature the efficacy of PEF/MF increased contrary to MF/PEF. Thus, PEF/MF represents a potential alternative for ‘cold’ pasteurisation of milk with improved quality.     

Vitamin D₂ impairs utilization of vitamin D₃ in high-yielding dairy cows in a cross-over supplementation regimen

Vitamin D exists in 2 forms that are important regarding vitamin D status and supply in cattle: vitamin D₂ (D₂) and vitamin D₃ (D₃). To become physiologically active, both D₂ and D₃ must undergo 25-hydroxylation in the liver. The resulting 25-hydroxyvitamin D₂ [25(OH)D₂] and 25-hydroxyvitamin D₃ [25(OH)D₃] are measured as indicators of the physiological vitamin D status of cattle. The study used 14 Danish Holstein cows housed without access to sunlight. The cows were orally administered 250 mg (1.0 × 10⁷ IU) of D₂ and D₃ in a cross-over design with 2 treatment groups and 2 study periods, rendering 4 treatments when carryover effects were taken into account: D₂ given first, D₂ given last after D₃, D₃ given first, and D₃ given last after D₂. Two weeks elapsed between the treatment in the first study period and the treatment in the second study period. Blood samples were collected 0, 3, 6, 14, 17, 20, 23, 26, 40, 48, 70, 94, 166, and 214 h after providing the oral bolus of vitamin to the cows. Comparisons between plasma levels of the metabolites D₂, D₃, 25(OH)D₂, and 25(OH)D₃ over time were made by comparing areas under the plasma concentration curves. Oral administration of D₃ increased plasma D₃ (182.6 ± 17.1 ng/mL; mean ± SEM) and 25(OH)D₃ (103.5 ± 10.0 ng/mL) more efficiently than oral administration of D₂ increased plasma D₂ (49.1 ± 32.6 ng/mL) and 25(OH)D₂ (27.9 ± 2.1 ng/mL). The D₃ given after an oral dose of D₂ was less efficient for increasing plasma concentrations of 25(OH)D₃ (61.2 ± 12.0 ng/mL) compared with D₃ given without previous D₂ administration (103.5 ± 10.0 ng/mL), whereas the plasma concentrations of D₃ itself were the same when given first (182.6 ± 17.1 ng/mL) as when given after D₂ (200.0 ± 123.9 ng/mL). The same occurred for plasma concentrations of D₂ metabolites both if D₂ was given first (49.1 ± 32.6 ng/mL) and after D₃ (54.7 ± 7.7 ng/mL). In conclusion, D₃ given after D₂ is less efficient at increasing the plasma status of 25(OH)D₃ than D₃ given without previous D₂ administration.     

Use of high-concentration-short-time chlorine dioxide gas treatments for the inactivation of Salmonella enterica spp. inoculated onto Roma tomatoes

Salmonella outbreaks have been recently linked to the consumption of fresh tomatoes. Thus, there is a need to develop systems that reduce the risk of microbial contamination to increase product shelf-life and keep fresh fruit attributes. The objectives of this study were to evaluate high-concentration-short-time chlorine dioxide gas treatments effects on Salmonella-inoculated Roma tomatoes and determine the optimal treatment conditions for microbial inactivation and shelf-life extension. Effects of ClO₂ concentration (2, 5, 8 and 10 mg/l) and exposure time (10, 30, 60, 120 and 180 s) on inoculated Roma tomatoes were studied. Salmonella enterica strains, serotype Montevideo, Javiana and Baildon, were used to experimentally inoculate the food product. After ClO₂ treatments, tomatoes were stored at room temperature for 28 days. Inherent microbial population, change in tomato color, and chlorine dioxide gas residuals were evaluated. ANOVA analysis showed that both ClO₂ concentration and treatment time were significant (p < 0.01) for Salmonella inactivation. Surviving Salmonella populations of 3.09, 2.17 and 1.16 log CFU/cm² were obtained treating tomatoes with 8 mg/l ClO₂ for 60 s, 10 mg/l ClO₂ for 120 s, and 10 mg/l for 180 s, respectively (initial Salmonella population: 6.03 ± 0.11 log CFU/cm²). The selected treatments significantly reduced background microflora (p < 0.05), while fruit color and residual contents were not significantly different (p > 0.05), as compared to the control. Results suggest the potential for high-concentration-short-time treatments ClO₂ gas as an effective pathogen inactivation technology for large-scale produce packing operations.     

Efficacy of neutral electrolyzed water for sanitization of cutting boards used in the preparation of foods

The effectiveness of neutral electrolyzed water (NEW) to sanitize cutting boards used for food preparation was investigated. Cutting boards made of hardwood and bamboo were inoculated with Escherichia coli K12 and Listeria innocua, dried for 1 h, washed, rinsed and sanitized with NEW, sodium hypochlorite (NaClO) solution, or tap water (control). After each washing protocol, surviving bacterial populations were determined. Results showed that both NEW and NaClO sanitizing solutions produced similar levels of bacterial reductions. In manual washing, the population reductions by NEW and NaClO were 3.4 and 3.6 log₁₀ CFU/100 cm² for E. coli, and 4.1 and 3.9 log₁₀ CFU/100 cm² for L. innocua, respectively. In the automatic washing, the reductions by NEW and NaClO were 4.0 and 4.0 log₁₀ CFU/100 cm² for E. coli, and 4.2 and 3.6 log₁₀ CFU/100 cm² for L. innocua, respectively. No significant differences (P > 0.05) were observed in surviving bacteria counts when comparing board material types.     

Survival of Escherichia coli O157:H7 in channel catfish pond and holding tank water

Survival of Escherichia coli O157:H7 in channel catfish (Ictalurus punctatus), pond and holding tank water was investigated. Water from three channel catfish ponds was inoculated with ampicillin/nalidixic acid-resistant E. coli O157:H7 transformed with a plasmid encoding for green fluorescent protein at 10⁵, 10⁶, and 10⁷ CFU/ml. Samples were taken from surface, internal organs, and skin scrape of fish and pond water for E. coli O157:H7 enumeration on brain heart infusion (BHI) agar containing ampicillin and nalidixic acid. To determine the survival of E. coli O157:H7 in catfish holding tank water from two farmers markets, the water was inoculated with 10⁷E. coli O157:H7 CFU/ml. E. coli O157:H7 were detected by direct plating for 33 and 69 d in pond and holding tank water, respectively. A rapid decrease of the pathogen was observed in the first 2 weeks to reach 2 log CFU/ml. When E. coli O157:H7 was not recovered by direct plating, the pathogen was isolated by enrichment in TSB for approximately another 30 d from pond and holding tank water. The populations of E. coli O157:H7 found in the internal organs and skin scrape were 5.5 log and 2.5 log CFU/ml, respectively. E. coli O157:H7 from internal organs and water were recovered for at least 12 d. Results suggest that E. coli O157:H7 can survive in channel catfish pond and holding tank water and channel catfish may become a potential carrier of the pathogen.