Effect of X-ray treatments on Escherichia coli O157:H7, Listeria monocytogenes, Shigella flexneri, Salmonella enterica and inherent microbiota on whole mangoes.

UNLABELLED: The aims of this investigation were to; (i) study the effect of X-ray treatments in reducing Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica and Shigella flexneri on whole mangoes, and (ii) study the effect of X-ray treatments on microflora counts (mesophilic counts, psychrotrophic counts and yeast and mould counts) of whole mangoes during storage at ambient temperature (22°C) for 30 days. A mixture of three strains of each test organism was spot inoculated (100 µl; approx. 8-9 log CFU ml(-1) ), separately, onto the surface (5 cm(2) ) of whole mangoes, air-dried (30 min), and then treated with different doses of X-ray (0, 0·1, 0·5, 1·0, and 1·5 kGy). Approximately 2·9, 1·8, 2·1 and 5·2 log CFU cm(-2) reduction of E. coli O157:H7, L. monocytogenes, Sh. flexneri and Salm. enterica were achieved by treatment with 0·5 kGy X-ray respectively. Furthermore, the populations of E. coli O157:H7, L. monocytogenes, Sh. flexneri and Salm. enterica were reduced to less than the detectable limit (2·0 log CFU cm(-2) ) by treatment with 1·5 kGy X-ray. Treatment with 1·5 kGy X-ray significantly reduced the initial inherent microflora on skin of whole mangoes and inherent levels were significantly (P < 0·05) lower than the control sample throughout storage at 22°C for 30 days. SIGNIFICANCE AND IMPACT OF THE STUDY: Fresh produce was associated with 770 outbreaks between 1990 and 2005, resulting in 35 060 cases of illness that costs the US $39 billion annually. The food industry is looking for new preservation methods. This investigation indicated that X-ray treatment was very effective against Escherichia coli O157:H7, Listeria monocytogenes, Shigella flexneri and Salmonella enterica and inherent microflora on whole mangoes which could offer an applicable approach to control pathogens and spoilage bacteria for the mango industry.

Controlling Vibrio vulnificus and spoilage bacteria in fresh shucked oysters using natural antimicrobials.

UNLABELLED: This study evaluated the efficacy of grape seed extract (GE), citric acid (CA) and lactic acid (LA) on the inactivation of Vibrio vulnificus and inherent microflora in fresh shucked oysters. The minimum inhibitory concentration (MIC) of GE, CA or LA against V. vulnificus was determined. Furthermore, the shucked oysters were artificially inoculated with V. vulnificus. The inoculated shucked oysters (25 g) were then dipped in 250 ml GE, CA or LA solutions for 10 min. The population of V. vulnificus in shucked oysters was determined. The effects of the treatments with GE, CA or LA solutions on the inherent microbiota in fresh shucked oysters during storage at 5°C for 20 days were also studied. The MICs of GE, CA or LA against V. vulnificus were 10.0, 5.0 or 1.0 mg ml(-1), respectively. The concentrations of 500, 300 or 150 mg ml(-1) GE, CA or LA solutions were needed to reduce the population of V. vulnificus to below the detection level (1.0 log g(-1)). Treatment with 500, 300, 150 mg ml(-1) GE, CA or LA significantly reduced the initial inherent microbiota in fresh shucked oysters, and inherent levels were significantly (P < 0.05) lower than the control sample throughout refrigerated storage for 20 days. SIGNIFICANCE AND IMPACT OF THE STUDY: Oysters filter large volume of seawater during their feeding activities that concentrate bacteria such as Vibrio vulnificus in their body. The presence of V. vulnificus in oysters has a serious impact on public health and international trade. There is increasing concern over the use of chemical preservatives. Furthermore, the food industry is looking for new natural preservation methods. This study indicated that lactic acid and citric acid wash solutions could offer an inexpensive, natural and strong approach to control V. vulnificus and spoilage bacteria in fresh shucked for the oyster industry.

Reduction in Listeria monocytogenes and spoilage bacteria on smoked catfish using X-ray treatments.

AIMS: To determine the efficacy of X-ray processes in inactivating L. monocytogenes levels in smoked catfish during storage at 5°C and to determine the effects of X-ray doses on controlling the growth of spoilage bacteria on smoked catfish during storage at 5°C for up to 5 weeks. METHODS AND RESULTS: Smoked catfish fillets inoculated with L. monocytogenes were treated with 0.0-2.0 kGy X-ray and stored at 5°C for 5 weeks. The negative controls (uninoculated/untreated) and uninoculated samples treated with the lowest (0.1 kGy) and highest (2.0 kGy) doses were stored at 5°C and tested for psychrotrophs count during the 5 weeks of storage. The initial L. monocytogenes population on smoked catfish was significantly (P < 0.05) reduced to undetectable level by a treatment of 1.0 kGy or higher. The initial psychrotrophs count on smoked catfish was significantly reduced from 4.7 CFU g(-1) to below the detectable level by a treatment with 2.0 kGy. CONCLUSIONS: Smoked catfish treated with 2.0 kGy X-ray had no detectable L. monocytogenes throughout 35 days of storage at 5°C. A treatment with 2.0 kGy X-ray also kept the levels of psychrotrophs in the smoked catfish within the acceptable level until 35 days. SIGNIFICANCE AND IMPACT OF THE STUDY: The results of this investigation indicate that X-ray at 2.0 kGy can eliminate L. monocytogenes and extend the shelf life of smoked catfish stored at refrigeration temperature.

Inactivation effect of X-ray treatments on Cronobacter species (Enterobacter sakazakii) in tryptic soy broth, skim milk, low-fat milk and whole-fat milk.

AIMS: To determine the inactivation effect of X-ray treatments on Cronobacter (E. sakazakii) in tryptic soy broth (TSB), skim milk (0% fat), low-fat milk (1% and 2%) and whole-fat milk (3.5%). METHODS AND RESULTS: X-rays were produced using the RS 2400 generator system (Rad Source Technologies Inc.). Cronobacter (in TSB), inoculated skim milk (0% fat), low-fat milk (1% and 2% fat) and whole-fat milk (3.5% fat) were treated with 0.0, 0.1, 0.5, 0.75, 1.0, 2.0, 3.0, 4.0, 5.0 and 6.0 kGy X-ray doses. Surviving bacteria in the TSB and inoculated milk, before and after treatment, were enumerated using plating method onto trypticase soy agar. Greater than 7.0-log CFU reduction in Cronobacter population was observed with 4.0, 5.0, 6.0, 6.0 and 6.0 kGy X-ray in the TSB, skim milk, 1% fat milk, 2% fat milk and 3.5% fat milk, respectively. CONCLUSIONS: Treatment with X-rays significantly (P < 0.05) reduced Cronobacter to less than detectable limits (<1 log CFU ml(-1)) in skim milk at 5.0 kGy and milk with 1% fat content and greater at 6.0 kGy dose levels. The D-value for Cronobacter in TSB was significantly (P < 0.05) lower than those in milk samples. SIGNIFICANCE AND IMPACT OF THE STUDY: Treatment with X-rays could be an effective and safe alternative technology to control pathogenic bacteria (Cronobacter) in the dairy industry.

Inactivation of Vibrio parahaemolyticus in pure culture, whole live and half shell oysters (Crassostrea virginica) by X-ray.

AIMS: To study the inactivation effect of different doses of X-ray on Vibrio parahaemolyticus in pure culture, inoculated whole live and half shell oysters and to evaluate the efficacy of X-ray doses on reduction of inherent microflora on oysters. METHODS AND RESULTS: X-ray was produced using RS 2400 generator system (Rad Source Technologies Inc.). Pure culture of V. parahaemolyticus, inoculated half and whole shell oysters with V. parahaemolyticus were treated with 0.0, 0.1, 0.5, 0.75, 1.0, 1.5, 2.0, 3.0 and 5.0 kGy X-ray. Surviving bacteria in the pure culture and inoculated oysters, before and after treatment, were enumerated using overlay plating (in TSA then TCBS) and most probable number (MPN) methods. A greater than 6.0 log reduction of V. parahaemolyticus was observed with 0.75, 2.0 and 5.0 kGy X-ray for pure culture, half shell and whole shell oysters, respectively. Treatment with 0.75, 2.0 and 5.0 kGy X-ray reduced the MPN to <3 for pure culture, half and whole shell oysters, respectively. Treatment with 1.0 kGy X-ray significantly (P < 0.05) reduced the inherent micro-organisms on whole shell oysters from 4.7 +/- 0.1 to less than the detectable limit (<1.0 log CFU g(-1)). CONCLUSIONS: X-ray (1-5 kGy) significantly (P < 0.05) reduced V. parahaemolyticus and inherent microflora on oysters to less than detectable limit (<1.0 log CFU g(-1)). SIGNIFICANCE AND IMPACT OF THE STUDY: Treatment with X-ray could control pathogenic bacteria and extend the shelf life of oysters.

Inactivation kinetics of inoculated Escherichia coli O157:H7, Listeria monocytogenes and Salmonella Poona on whole cantaloupe by chlorine dioxide gas.

The objectives of this study were to examine inactivation kinetics of inoculated Escherichia coli O157:H7, Listeria monocytogenes and Salmonella Poona inoculated onto whole cantaloupe and treated with ClO(2) gas at different concentrations (0.5, 1.0, 1.5, 3.0 and 5.0 mg l(-1)) for different times (0, 2.0, 4.0, 6.0, 8.0 and 10.0 min). The effect of ClO(2) gas on the quality and shelf life of whole cantaloupe was also evaluated during storage at 22 degrees C for 12 days. A 100 microl inoculation of each targeted organism was spotted onto the surface (5 cm(2)) of cantaloupe rind (approximately 8-9 log CFU 5 cm(-2)) separately, air dried (60 min), and then treated with ClO(2) gas at 22 degrees C and 90-95% relative humidity for 10 min. Surviving bacterial populations on cantaloupe surfaces were determined using a membrane transferring method with a non-selective medium followed by a selective medium. The inactivation kinetics of E. coli O157:H7, L. monocytogenes and S. Poona were determined using nonlinear kinetics (Weibull model). A 3 log CFU reduction of E. coli O157:H7, L. monocytogenes and S. Poona were achieved with 5.0 mg l(-1) ClO(2) gas for 5.5, 4.2 and 1.5 min, respectively. A 5l og CFU reduction of S. Poona was achieved with 5.0 and 3.0 mg l(-1) ClO(2) gas for 6 and 8 min, respectively. A 4.6 and 4.3 log reduction was achieved after treatment with 5.0 mg l(-1) ClO(2) gas at 10 min for E. coli O157:H7 and L. monocytogenes, respectively. Treatment with 5.0 mg l(-1) ClO(2) gas significantly (p<0.05) reduced the initial microflora (mesophilic bacteria, psychrotrophic bacteria, and yeasts and molds) on cantaloupe by more than 2 log CFU cm(-2) and kept them significantly (p<0.05) lower than the untreated control during storage at 22 degrees C for 12 days. Treatment with ClO(2) gas did not significantly (p>0.05) affect the color of whole cantaloupe and extended the shelf life to 9 days compared to 3 days for the untreated control, when stored at ambient temperature (22 degrees C).

Inactivation kinetics of inoculated Escherichia coli O157:H7 and Salmonella enterica on lettuce by chlorine dioxide gas.

The purpose of this investigation was to study inactivation kinetics of inoculated Escherichia coli O157:H7 and Salmonella enterica on lettuce leaves by ClO(2) gas at different concentrations (0.5, 1.0, 1.5, 3.0, and 5.0 mg l(-1)) for 10 min and to determine the effect of ClO(2) gas on the quality and shelf life of lettuce during storage at 4 degrees C for 7 days. One hundred microliters of each targeted organism was separately spot-inoculated onto the surface (5 cm(2)) of lettuce (approximately 8-9 log CFU ml(-1)), air-dried, and treated with ClO(2) gas at 22 degrees C and 90-95% relative humidity for 10 min. Surviving bacterial populations on lettuce were determined using a membrane transferring method, which included a non-selective medium followed by a selective medium. The inactivation kinetics of E. coli O157:H7 and S. enterica was determined using first-order kinetics to establish D-values and z-values. The D-values of E. coli and S. enterica were 2.9+/-0.1 and 3.8+/-0.5 min, respectively, at 5.0 mg l(-1) ClO(2) gas. The z-values of E. coli and S. enterica were 16.2+/-2.4 and 21.4+/-0.5 mg l(-1), respectively. A 5 log CFU reduction (recommended by the United States Food and Drug Administration) for E. coli and S. enterica could be achieved with 5.0 mg l(-1) ClO(2) gas for 14.5 and 19.0 min, respectively. Treatment with ClO(2) gas significantly reduced inherent microflora on lettuce and microbial counts remained significantly (p<0.05) lower than the uninoculated control during storage at 4 degrees C for 7 days. However, treatment with ClO(2) gas had a significantly (p<0.05) negative impact on visual leaf quality. These results showed that treatment with ClO(2) gas significantly reduced selected pathogens and inherent microorganisms on lettuce; however, the processing conditions would likely need to be altered for consumer acceptance.

Decontamination effect of electrolysed NaCl solutions on carp.

AIMS: To evaluate the efficacy of electrolysed NaCl solutions (EW) for disinfecting bacterial isolates from carp, and the potential application of EW to reducing the bacterial load in whole carp and carp fillets. METHODS AND RESULTS: EW was produced by using a two-compartment batch-type electrolysed apparatus. Pure cultures (in vitro), whole carp (skin surface) and carp fillets were treated with EW to detect its antimicrobial effects. The anodic solution [EW (+)] completely inhibited growth of the isolates. Furthermore, dipping the fish samples in EW (+) reduced the mean total count of aerobic bacteria on the skin of whole carp and in fillets by 2.8 and 2.0 log(10), respectively. The cathodic solution [EW (-)] also reduced growth of the isolates from carp by ca 1.0 log(10). Moreover, the total counts of aerobic bacteria in whole carp (on the skin) and fillets were reduced by 1.28 and 0.82 log(10), respectively. CONCLUSIONS: EW (+) has a strong bactericidal effect on bacteria isolated from carp. SIGNIFICANCE AND IMPACT OF THE STUDY: Treatment with EW (+) could extend the shelf life of these fish.