Comparative studies on the yield and characteristics of myofibrillar proteins from catfish heads and frames extracted by two methods for making surimi-like protein gel products.

Fish protein isolates (FPI) were recovered from catfish heads and frames by alkaline extraction (AE) and salt extraction (SE) and made into surimi-like gels. Protein patterns and content, moisture, color, and texture of cooked protein gels were compared with commercial products. Sodium-dodecyl-sulfate poly acrylamide gel electrophoreses (SDS-PAGE) indicated that the integrity of major myofibrillar proteins was maintained during the extraction process, and the protein patterns were almost the same with that of the commercial surimi products. The yields of AE-FPI (heads: 36%; frames: 55%) were much higher (p < 0.05) than that of SE-FPI (heads: 9%; frames: 16%). Firmness of cooked protein gels made from heads was similar with that made from frames. Firmness of cooked protein gels made from FPI extracted by the SE method (heads: 0.45 kg/cm2; frames: 0.43 kg/cm2) was significantly lower (p < 0.05) than that made from FPI extracted by the AE method (heads: 1.96 kg/cm2; frames: 1.85 kg/cm2).

Synergistic activity between lauric arginate and carvacrol in reducing Salmonella in ground turkey.

In the present study, low concentrations of carvacrol (0.025 to 0.2%) and lauric arginate (LAE; 25 to 200 ppm) were tested at 4, 22, and 45°C in a broth model, and higher concentrations of carvacrol (0.1 to 5%) and LAE (200 to 5,000 ppm) were tested individually and in combination at 4°C in 3 different ground turkey samples (with 15, 7, and 1% fat content) for their effectiveness against a 3-strain mixture of Salmonella. A low concentration of 25 ppm of LAE or 0.025% carvacrol had no effect on Salmonella in a broth model, but their mixture showed a synergistic action by reducing 6 log cfu/mL Salmonella counts to a nondetectable level within 30 min of exposure. The US Food and Drug Administration-recommended 200 ppm of LAE was not sufficient for Salmonella reductions in ground turkey when applied internally. High concentrations of 2,000 to 5,000 ppm of LAE or 1 to 2% carvacrol were needed to reduce Salmonella counts by 2 to 5 log cfu/g in ground turkey by internal application. No specific relationship existed between fat content and LAE or carvacrol concentrations for Salmonella reductions. For example, 2,000 ppm of LAE could reduce Salmonella counts by 4 log cfu/g in 1% fat-containing turkey samples but very similar ~1.5 log cfu/g reductions in both 7 and 15% fat-containing ground turkey samples. For the total microbial load, about 2,000 ppm of LAE or 2% of carvacrol treatments were needed to achieve 2 to 3 log (P ≤ 0.05) cfu/g reductions in different turkey samples. A mixture of 1% carvacrol and 2,000 ppm of LAE exhibited a synergistic action in ground turkey containing 7% fat by reducing the Salmonella counts by 4 log cfu/g, which was not found with individual antimicrobial treatments.

Effect of x-ray treatments on pathogenic bacteria, inherent microbiota, color, and texture on parsley leaves.

This work is a part of systematic studies of the effect of X-ray treatments on fresh produce. The main objective of this investigation was to study the effects of X-ray treatments in reducing the concentration of artificially inoculated Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica, and Shigella flexneri, and inherent microbiota on parsley leaves. The secondary objective was to study the effects of X-ray treatments on color and texture parameters on treated parsley leaves. The Dip-inoculated method was used to inoculate parsley leaves with a mixture of two or three strains of each tested organism at 10(8) to 10(9) colony-forming unit (CFU)/mL; the inoculated parsley leaves were then air-dried and followed by treatment with different doses of X-ray (0, 0.1, 0.5, 1.0, and 1.5 kGy) at 22°C and 55-60% relative humidity. Surviving bacterial populations on parsley leaves were evaluated using a nonselective medium (tryptic soy agar) with a selective medium overlay for each bacterium: E. coli O157:H7 (CT-SMAC agar), L. monocytogenes (MOA), and S. enterica and S. flexneri (XLD). Approximately 5.8, 3.1, 5.7, and 5.2 log CFU reductions of E. coli O157:H7, L. monocytogenes, S. enterica, and Shigella flexneri were achieved by treatment with 1.0 kGy X-ray, respectively. Furthermore, the populations of E. coli O157:H7, L. monocytogenes, S. enterica, and Shigella flexneri were reduced to less than the detectable limit (1.0 log CFU/g) by treatment with 1.5 kGy X-ray. Treatment with 1.5 kGy X-ray significantly reduced the initial inherent microbiota on parsley leaves, and inherent levels were significantly (p < 0.05) lower than the control sample throughout refrigerated storage for 30 days. No significant differences (p > 0.05) in color or texture of control and treated samples with 0.1-1.5 X-ray were observed. The results of investigation indicated that X-ray is an effective technology to eliminate E. coli O157:H7, L. monocytogenes, S. enterica, and Shigella flexneri, and to extend the shelf life of parsley leaves.

Control of Listeria monocytogenes and spoilage bacteria on smoked salmon during storage at 5 °C after X-ray irradiation.

In this study, smoked salmon fillets were artificially inoculated with Listeria monocytogenes (3.7 ± 0.2 log CFU g(-1)) and treated with X-ray irradiation generated by a RS 2400 X-ray machine (Rad Source Technologies Inc.) using doses of 0.0, 0.1, 0.5, 1.0, and 2.0 kGy. Unirradiated and irradiated samples were then stored at 5 °C for 35 days and tested for L. monocytogenes count after 0, 5, 10, 15, 20, 25, 30, and 35 days. Also, uninoculated-untreated and uninoculated-treated samples with the lowest and highest X-ray doses (0.1 and 2.0 kGy) were stored at 5 °C and examined for psychrotrophs and mesophiles counts after 0, 5, 10, 15, 20, 25, 30, and 35 days. The initial L. monocytogenes population (3.7 log CFU g(-1) ) was significantly (p < 0.05) reduced to an undetectable level (<1.0 log CFU g(-1)) by treatment with 1.0 kGy X-ray. Treatment with 0.1 kGy X-ray significantly reduced the initial psychrotrophs and mesophiles counts from 5.3 and 3.0 to 3.3 and 2.3, respectively. However, L. monocytogenes, psychrotrophs and mesophiles counts were gradually increased during storage. Treatment with 2.0 kGy X-ray kept the L. monocytogenes population under detectable level until 35 days. Treatment with 2.0 kGy X-ray kept the mesophiles and psychrotrophs counts within the acceptable level until 35 days. These results revealed that treatment with X-ray irradiation can significantly reduce the risk of listeriosis and extend the shelf life of smoked salmon during storage at 5 °C.

Effects of X-ray treatments on pathogenic bacteria, inherent microflora, color, and firmness on whole cantaloupe.

Inactivation of inoculated Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica and Shigella flexneri on whole cantaloupes using X-ray at different doses (0.1, 0.5, 1.0, 1.5, and 2.0 kGy) was studied. The effect of X-ray on quality parameters (color and texture) of untreated and treated whole cantaloupes was instrumentally determined. The effect of X-ray on microflora counts (mesophilic counts, psychrotrophic counts and yeast and mold counts) of untreated and treated whole cantaloupes was also determined during storage at 22°C for 20 days. A mixture of three strains of each tested organism was spot inoculated (100 µl), separately, onto the surface (5 cm(2)) of cantaloupe rinds (approximately 8-9 log CFU ml(-1)) separately, air dried (60 min), and then treated with X-ray at 22°C and 55% relative humidity. Surviving bacterial populations on cantaloupe surfaces were evaluated using a nonselective medium (tryptic soy agar) with a selective medium overlay for each bacterium; E. coli O157:H7 (CT-SMAC agar), L. monocytogenes (MOA), and S. enterica and S. flexneri (XLD). More than a 5 log CFU reduction was achieved after treatment with 2.0 kGy X-ray, for all tested pathogens. No significant effect of X-ray treatment on cantaloupe color or firmness was detected. Furthermore, treatment with X-ray significantly reduced the initial inherent microflora on whole cantaloupes and inherent levels were significantly (p<0.05) lower than the control sample throughout storage for 20 days.

Effect of chlorine dioxide gas on Salmonella enterica inoculated on navel orange surfaces and its impact on the quality attributes of treated oranges.

Microorganisms, including pathogens of public health significance, have been shown to contaminate orange juice during the mechanical extraction of juice. The problem gets exacerbated when washed oranges have high initial microbial load, due to an insufficient postharvest treatment. The objective of this study was to investigate the reduction of Salmonella enterica on orange surfaces using ClO2 gas treatments to achieve a 5 log reduction, consistent with the recommendations of the U.S. Department of Agriculture-National Advisory Committee on Microbiological Criteria for Foods. A mixed culture of four Salmonella strains, isolated from previous orange juice outbreaks, was spot inoculated onto orange skin surface areas. The oranges were then treated with 0.1, 0.3, and 0.5 mg/L ClO2 gas for 2-14 minutes at 22°C and 90%-95% relative humidity. Surviving bacteria on treated areas were recovered and enumerated over treatment time on a nonselective medium, tryptic soy agar, followed by culturing onto a selective medium, xylose lysine deoxycholate agar. A >5 log reduction of Salmonella per sample of orange surface was observed with 0.1 and 0.3 mg/L ClO2 gas treatments at 14 minutes and a similar log reduction was observed at 0.5 mg/L ClO2 gas at 10 minutes. This result demonstrates that the treatment of oranges with ClO2 gas is a promising technology that could be successfully employed for the treatment of whole oranges to reduce the risk of Salmonella outbreaks in orange juice.

The effects of X-ray radiation on Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica and Shigella flexneri inoculated on whole Roma tomatoes.

In the last two decades several foodborne disease outbreaks associated with produce were reported. Tomatoes, in particular, have been associated with several multi-state Salmonella outbreaks. Inactivation of inoculated Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica and Shigella flexneri on whole Roma tomato surfaces by X-ray at 0.1, 0.5, 0.75, 1.0, and 1.5 kGy was studied. The main purpose of this study was to achieve a 5 log reduction in consistent with the recommendations of the National Advisory Committee on Microbiological Criteria for Foods. Moreover, the effect of X-ray on inherent microflora (mesophilic counts, psychrotrophic counts and yeast and mold counts) of untreated and treated Roma tomatoes, during storage at ambient temperature (22°C) for 20 days was also determined. Mixtures of three or two strains of each tested organism was spot inoculated (100 µl) onto the surface of Roma tomatoes (approximately 7-9 log per tomato), separately, and air-dried, followed by treatment with X-ray doses at 22°C and 55-60% relative humidity. Surviving bacterial populations on tomato surfaces were evaluated using a nonselective medium (tryptic soy agar) with a selective medium overlay for each bacteria; E. coli O157:H7 (CT-SMAC agar), L. monocytogenes (MOA), and S. enterica and S. flexneri (XLD). Treatment with X-ray significantly reduced the population of the tested pathogens on whole Roma tomato surfaces, compared with the control. Approximately 4.2, 2.3, 3.7 and 3.6 log CFU reduction of E. coli O157:H7, L. monocytogenes, S. enterica and S. flexneri per tomato were achieved by treatment with 0.75 kGy X-ray, respectively. More than a 5 log CFU reduction per tomato was achieved at 1.0 or 1.5 kGy X-ray for all tested pathogens. Furthermore, treatment with X-ray significantly reduced the inherent microflora on Roma tomatoes. Inherent levels were significantly (p<0.05) lower than the control sample throughout storage for 20 days.

Inactivation of Salmonella enterica and Listeria monocytogenes inoculated on hydroponic tomatoes using chlorine dioxide gas.

The main objective of this study was to determine survivability of a cocktail of three strains of Salmonella enterica (Montevideo, Javiana, and Baildon) and two strains of Listeria monocytogenes (LCDC 81-861 and F4244) on hydroponic tomatoes after treatment with chlorine dioxide (ClO(2)) gas. An initial concentration of 8-9 log cfu/mL of Salmonella and Listeria cocktails was inoculated individually, in separate experiments, on tomato skin to obtain a population of 7-8 log cfu/cm(2) after drying of the inoculums on the tomato skin. The aim was to achieve a 5 log reduction consistent with the recommendations of the National Advisory Committee on Microbiological Criteria for Foods. The tomato skins were treated with 0.1, 0.3, and 0.5 mg/L ClO(2) gas for 12 min at 22 degrees C and at the relative humidity of 90%. Untreated skin samples were processed under the same conditions. ClO(2)-gas-treated and untreated samples were recovered by an overlay method. The bottom layer contains tryptic soy agar, and the top layer consists of xylose-lysine-desoxycholate agar or modified Oxford antimicrobial supplement agar for Salmonella and Listeria, respectively. More than a 5 log reduction in Salmonella and Listeria was observed on the tomato skin surfaces after treatment with 0.5 mg/L ClO(2) gas for 12 min. Treatment with 0.5 mg/L ClO(2) gas for 12 min also delayed the growth of natural microflora on tomato surfaces and extended the shelf life of tomatoes by 7 days during storage at 22 degrees C, compared with the untreated control. These results revealed that ClO(2) gas is a promising antimicrobial technology for fresh tomato skin surfaces.

Inactivation of Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica and Shigella flexneri on spinach leaves by X-ray.

Several recent foodborne disease outbreaks associated with leafy green vegetables, including spinach, have been reported. X-ray is a non-thermal technology that has shown promise for reducing pathogenic and spoilage bacteria on spinach leaves. Inactivation of inoculated Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica and Shigella flexneri on spinach leaves using X-ray at different doses (0.1, 0.2, 0.3, 0.5, 0.75, 1.0, 1.5 and 2.0 kGy) was studied. The effect of X-ray on color quality and microflora counts (mesophilic counts, psychrotrophic counts and yeast and mold counts) of untreated and treated spinach was also determined. A mixture of three strains of each tested organism was spot inoculated (100 microl) onto the surface of spinach leaves (approximately 8-9 log ml(-1)), separately, and air-dried, followed by treatment with X-ray at 22 degrees C and 55-60% relative humidity. Surviving bacterial populations on spinach leaves were evaluated using a nonselective medium (tryptic soy agar) with a selective medium overlay for each bacteria; E. coli O157:H7 (CT-SMAC agar), L. monocytogenes (MOA), and S. enterica and S. flexneri (XLD). More than a 5 log CFU reduction/leaf was achieved with 2.0 kGy X-ray for all tested pathogens. Furthermore, treatment with X-ray significantly reduced the initial inherent microflora on spinach leaves and inherent levels were significantly (p < 0.05) lower than the control sample throughout refrigerated storage for 30 days. Treatment with X-ray did not significantly affect the color of spinach leaves, even when the maximum dose (2.0 kGy) was used.

Effects of X-ray radiation on Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica and Shigella flexneri inoculated on shredded iceberg lettuce.

The main goal of this investigation was to study the efficacy of X-ray doses (0.1, 0.2, 0.3, 0.5, 0.75, 1.0, 1.5 and 2.0 kGy) on inoculated Escherichia coli O157: H7, Listeria monocytogenes, Salmonella enterica and Shigella flexneri on shredded iceberg lettuce. The second goal was to study the effect of X-ray on the inherent microflora counts and visual color of shredded iceberg lettuce during storage at 4 degrees C for 30 days. Treatment with 1.0 kGy X-ray significantly reduced the population of E. coli O157: H7, L. monocytogenes, Salmonella enterica and S. flexneri on shredded iceberg lettuce by 4.4, 4.1, 4.8 and 4.4-log CFU 5 cm(-2), respectively. Furthermore, more than a 5 log CFU reduction of E. coli O157: H7, L. monocytogenes, S. enterica and S. flexneri was achieved with 2.0 kGy X-ray. Treatment with X-ray reduced the initial microflora on iceberg lettuce and kept them significantly (p < 0.05) lower than the control during storage at 4 degrees C and 90% RH for 30 days. Treatment with X-ray did not significantly (p > 0.05) change the green color of iceberg lettuce leaves. Treatment with X-ray significantly reduced selected pathogens and inherent microorganisms on shredded iceberg lettuce leaves, which could be a good alternative to other technologies for produce (lettuce) industry.

Effect of X-ray treatments on inoculated Escherichia coli O157: H7, Salmonella enterica, Shigella flexneri and Vibrio parahaemolyticus in ready-to-eat shrimp.

This study was conducted to evaluate the inactivation effect of X-ray treatments on Escherichia coli O157: H7, Salmonella enteric (S. enterica), Shigella flexneri (S. flexneri) and Vibrio parahaemolyticus (V. parahaemolyticus) artificially inoculated in ready-to-eat (RTE) shrimp. A mixed culture of three strains of each tested pathogen was used to inoculate RTE shrimp. The shrimp samples were inoculated individually with selected pathogenic bacteria then aseptically placed in sterile plastic cups and air-dried at 22 degrees C for 30 min (to allow bacterial attachment) in the biosafety cabinet prior to X-ray treatments. The inoculated shrimp samples were then placed in sterilized bags and treated with 0.1, 0.2, 0.3, 0.5, 0.75, 1.0, 2.0, 3.0 and 4.0 kGy X-ray at ambient temperature (22 degrees C and 60% relative humidity). Surviving bacterial populations were evaluated using a non-selective medium (TSA) with the appropriate selective medium overlay for each bacterium; CT-SMAC agar for E. coli O157: H7, XLD for S. enterica and S. flexneri and TCBS for V. parahaemolyticus. More than a 6 log CFU reduction of E. coli O157: H7, S. enterica, S. flexneri and V. parahaemolyticus was achieved with 2.0, 4.0, 3.0 and 3.0 kGy X-ray, respectively. Furthermore, treatment with 0.75 kGy X-ray significantly reduced the initial microflora on RTE shrimp samples from 3.8 +/- 0.2 log CFU g(-1) to less than detectable limit (<1.0 log CFU g(-1)).

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

The purpose of this investigation was to study the inactivation effect of X-ray treatments on inoculated Vibrio vulnificus in pure culture, half shell and whole shell oysters to achieve a 5.0 log reduction, which is recommended by the Interstate Shellfish Sanitation Conference and the Food and Drug Administration. A mixed culture of three V. vulnificus strains was used to prepare the pure culture and inoculated oysters. The pure culture and inoculated oysters were treated with 0.0, 0.1, 0.5, 0.75, 1.0, 1.5, 2.0, and 3.0 kGy X-ray at 22 degrees C and 50-60% relative humidity. Surviving bacterial populations in the pure culture and inoculated oysters were enumerated using overlay-plating method [with a non-selective media (trypticase soy agar) followed by a selective medium (Modified Cellobiose-Polymyxin B-Colistin) and most probable number (MPN) method. Greater than a 6-log reduction of V. vulnificus was achieved with 0.75, 1.0 3.0 kGy X-ray in pure culture, half shell and whole shell oysters, respectively. Treatment with 0.75 kGy X-ray significantly (p<0.05) reduced the inherent microorganisms in half shell oysters, to less than the detectable limit (<1 log CFU/g). The maximum dose (3.0 kGy) of X-ray treatment did not affect the survivability of live oysters.

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

Inactivation kinetics of inoculated Escherichia coli O157:H7, Listeria monocytogenes and Salmonella enterica on strawberries by chlorine dioxide gas at different concentrations (0.5, 1, 1.5, 3 and 5 mgl(-1)) for 10 min were studied. A cocktail of three strains of each targeted organism (100 microl) was spotted onto the surface of the strawberries (approximately 8-9 log ml(-1)) separately followed by air drying, and then treated with ClO(2) gas at 22 degrees C and 90-95% relative humidity. Approximately a 4.3-4.7 logCFU reduction per strawberry of all examined bacteria was achieved by treatment with 5 mgl(-1) ClO(2) for 10 min. The inactivation kinetics of E. coli O157:H7, L. monocytogenes and S. enterica were determined using first-order kinetic models to establish D-values and z-values. The D-values of E. coli, L. monocytogenes and S. enterica were 2.6+/-0.2, 2.3+/-0.2 and 2.7+/-0.7 min, respectively, at 5 mgl(-1) ClO(2). The z-values of E. coli, L. monocytogenes and S. enterica were 16.8+/-3.5, 15.8+/-3.5 and 23.3+/-3.3 mgl(-1), respectively. Furthermore, treatment with ClO(2) gas significantly (p < or = 0.05) reduced the initial microflora (mesophilic, psychrotrophic bacteria, yeasts and molds) on strawberries. Treatment with ClO(2) gas did not affect the color of strawberries and extended the shelf-life to 16 days compared to 8 days for the untreated control.

Preservative effect of combined treatment with electrolyzed NaCl solutions and essential oil compounds on carp fillets during convectional air-drying.

The antimicrobial and antioxidant effects on carp fillet samples of treatments with alkaline electrolyzed NaCl solution EW (-) prior to treatment with acidic electrolyzed NaCl solution EW (+) and 1% solutions of the essential oils consisting of 0.5% carvacrol and 0.5% thymol (1% Cv+Ty) were tested. First carp fillet samples were treated with EW (-), then EW (+), followed by 1% (C+T), represented as [EW (-)/EW (+)/1% (Cv+Ty)] for 15 min, during drying at 45 degrees C. Samples were subsequently evaluated by microbiological, chemical and sensory analyses. Microbiological analyses indicated that the initial total microbial counts of samples treated with EW (-)/EW (+), 1% (Cv+Ty) or EW (-)/EW (+)/1% (Cv+Ty) were significantly (p< or =0.05) reduced, compared with the control sample. Treatment with EW (-)/EW (+)/1% (Cv+Ty) gave the strongest overall inhibition of microbial growth when compared to all of the other treatments. The volatile basic nitrogen (VBN) value of samples treated with EW (-)/EW (+)/1% (Cv+Ty) was kept at low level (18.46+/-0.45) until the end of drying period (5 days), compared with control samples (40.33+/-0.58). Treatment with EW (-)/EW (+)/1% (Cv+Ty) during drying significantly reduced the peroxide values (PV) and thiobarbituric acid values (TBA). Sensory evaluation indicated that there were significant differences (p< or =0.05) in the color, odor, taste, flavor and texture, on the end of the 5-day drying period between samples treated with EW (-)/EW (+)/1% (Cv+Ty), as compared to all of the other treatments. We conclude that treatment with EW (-)/EW (+)/1% (Cv+Ty) had stronger antimicrobial and antioxidant effects than all of the other treatments on carp fillets during drying, and could be a good alternative to artificial preservatives in food industry.