Taejo Kim

EFFECTS OF UV IRRADIATION ON SELECTED PATHOGENS IN PEPTONE WATER AND ON STAINLESS STEEL AND CHICKEN MEAT

Effects of intensity and processing time of 254 nm UV irradiation on Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella Typhimurium were investigated. Intensities measured at 5.08, 10.1, 15.2, and 20.3 cm from the light source were 1.000, 500, 250, and 150 microW/cm2, respectively. Intensities of 250 or 500 microW/cm2 reduced all suspended pathogen cells in peptone water about 5 log cycles after 2 min and completely inactivated L. monocytogenes and E. coli O157:H7 after 3 min by reductions of 8.39 and 8.64 log cycles, respectively. Intensities of 250 or 500 microW/cm2 also reduced (P < or = 0.05) the tested pathogens inoculated on stainless steel (SS) chips, and E. coli O157:H7 was completely destroyed at 500 microW/cm2 for 3 min. After UV treatment for 3 min at 500 microW/cm2, all selected pathogens on chicken meat with or without skin showed reduction ranges from 0.36 to 1.28 log cycles. Results demonstrated that UV irradiation could effectively decrease pathogens in peptone water and on SS but that it was less effective on chicken meat.

Prevalence and contamination patterns of Listeria monocytogenes in catfish processing environment and fresh fillets.

Catfish skins, intestines, fresh fillets, processing surfaces at different production stages, chiller water and non-food contact surfaces were sampled for Listeria monocytogenes and other Listeria species. Among 315 samples, prevalence of L. monocytogenes, Listeria innocua and a group of Listeria seeligeri-Listeria welshimeri-Listeria ivanovii was 21.6, 13.0 and 29.5%, respectively. No Listeria grayi was detected in this survey. While no L. monocytogenes strains were isolated from catfish skins and intestines, the strains were found with a frequency of 76.7% in chilled fresh catfish fillets and 43.3% in unchilled fillets. L. monocytogenes and Listeria spp. were also detected in fish contact surfaces such as deheading machine, trimming board, chiller water, conveyor belts at different stages, and fillet weighing table. Among L. monocytogenes, 1/2b (47.0%), 3b (16.0%) and 4c (14%) were the predominant serotypes isolated, whereas 4b, 4e, 1/2c and 1/2a were detected at much lower frequencies. Genotype analyses of L. monocytogenes isolates using serotyping, pulsed-field gel electrophoresis (PFGE) and enterobacterial repetitive intergenic consensus (ERIC)-PCR revealed that chiller water represented an important contamination source of L. monocytogenes in the chilled catfish fillets of two processing facilities, whereas fillet weighing table significantly contributed to the catfish fillet contamination of the third facility. This study suggests that L. monocytogenes contamination in the processed catfish fillets originates from the processing environment, rather than directly from catfish. Results from this study can aid the catfish industry to develop a plant-specific proper cleaning and sanitation procedure for equipment and the processing environment designed to specifically target L. monocytogenes contamination.

Antibiotic resistance in Listeria species isolated from catfish fillets and processing environment.

Aims:  To investigate the susceptibility of 221 Listeria spp. (86 Listeria monocytogenes, 41 Listeria innocua and 94 Listeria seeligeri‐Listeria welshimeri‐Listeria ivanovii) isolated from catfish fillets and processing environment to 15 antibiotics.

Enhanced antimicrobial activity of starch-based film impregnated with thermally processed tannic acid, a strong antioxidant.

Starch-based films impregnated with fresh tannic acid (FTA/starch film) and thermally processed tannic acid (PTA/starch film) were assessed for inhibition of Escherichia coli O157:H7 and Listeria monocytogenes. Disc-diffusion assay revealed that the PTA/starch film showed larger clear zone around the film on the bacterial lawn than the FTA/starch film at the same tannic acid concentrations (0.45 to 4.5mg per disc). Viable cell count assays in tryptic soy broth showed that the PTA/starch film also had a stronger antimicrobial activity on these foodborne pathogens than the FTA/starch film. L. monocytogenes did not replicate in trypic soy broth containing the FTA/starch film for the first 8h but multiplied up to 9.22 log CFU/ml at 48 h of incubation. The PTA/starch film caused a 2.72-log decrease in L. monocytogenes cells over the same time period. While 5-log E. coli O157:H7 cells were inactivated by the FTA/starch film within 48 h, more than 7-log E. coli O157:H7 cells were killed by the PTA/starch film over the same period. The antimicrobial activity of FTA/starch and PTA/starch film was primarily pH independent. HPLC measurement of the FTA or PTA release from starch film in water revealed that their release kinetic curves were in well match with their inactivation curves for E. coli O157:H7 and L. monocytogenes in 0.1% peptone water. In addition to antimicrobial activity, FTA showed antioxidant activity on soybean oil by doubling the induction time of oil oxidation. PTA further enhanced the oxidative stability of the oil by 17%. These results suggested that the use of processed tannic acid in starch films could improve the safety and quality of foods.

Antimicrobial Effect of Water-Soluble Muscadine Seed Extracts on Escherichia coli O157:H7

Water-soluble extracts were prepared from purple (cultivar Ison) and bronze (cultivar Carlos) muscadine seeds with or without heating. The Ison extracts had strong antimicrobial activity against a cocktail of three strains of Escherichia coli O157: H7. This extract had higher acidity (pH 3.39 to 3.43), total phenolics (2.21 to 3.49 mg/ml), tartaric acid (5.6 to 10.7 mg/ml), tannic acid (5.7 to 8.1 mg/ml), and gallic acid (0.33 to 0.59 mg/ml) than did the Carlos extracts. Heat treatment on both extracts increased antimicrobial activity, possibly because of increased acidity, tartaric acid, total phenolics, and individual phenolics. Heating of Ison extracts increased ellagic acid up to 83%. Up to 10.7 mg/ml tartaric acid alone was not as effective against E. coli O157:H7 as were water-soluble seed extracts. This finding suggests the involvement of other factors, such as tannic and gallic acids, in inactivation of this pathogen. Water-soluble muscadine seed extracts may be useful for incorporation into juice and other beverage products as natural preservatives.

Identification of Natural Antimicrobial Substances in Red Muscadine Juice against Cronobacter sakazakii

Red muscadine (Vitis rotundifolia Michx.) juices with natural organic, phenolic acids and polyphenol compounds were tested against Cronobacter sakazakii. The concentration of total phenolic compounds of commercial baby juices ranged from 176.7 to 347.7 mg/mL. Commercial baby juices showed poor antimicrobial activity, reducing less than 1-log of C. sakazakii in juice samples for 2 h at 37 degrees C. Red muscadine juices, regardless of processing methods (filtration, pasteurization, and sterilization), achieved a 6-log reduction of C. sakazakii in the same time period (2 h). The mixture of synthetic organic acids (malic and tartaric acids) and polyphenolic acid (tannic acid) showed strong antimicrobial activity against C. sakazakii. Among synthetic organic acids, tannic acid was undetected in commercial baby juices. Tannic acid showed the highest antimicrobial activity (1.4- to 3.8-log reduction) against C. sakazakii, while malic and tartaric acids showed less than 0.5-log reduction. These results suggest that red muscadine juice could be utilized as a natural antimicrobial in baby food formulations to inhibit C. sakazakii.

Antibacterial activity of fresh and processed red muscadine juice and the role of their polar compounds on Escherichia coli O157:H7

Aims:  The objectives of this research were to show the anti‐Escherichia coli O157:H7 effect of fresh (FRMJ) and processed red muscadine (Vitis rotundifolia) juice (PRMJ) and to discern the active compounds responsible for anti‐E. coli O157:H7.

Phosphate Type Affects the Quality of Injected Catfish Fillets

UNLABELLED Catfish fillets were injected to 115% over green weight prior to tray-packing and storage at 4 degrees C for 1, 4, 8, and 11 d. Fillets were evaluated for yields, surface color, pH, cooking loss, tenderness, purge loss, and shelf-life. All phosphate treatments increased (P < 0.05) fillet tenderness, but the agglomerated blend of sodium phosphates (AGSP) increased (P < 0.05) pH and yields, and decreased (P < 0.05) CIE L* and CIE b* values. Psychrotrophic plate counts (PPC) of fillets treated with the agglomerated blend of polyphosphates (AGPP) were lower (P < 0.05) than the control at each storage time, but PPC of all samples reached 7 log CFU/g by day 8 of storage. All agglomerated phosphates and STP (sodium tripolyphosphate) improved yields and quality when compared to the nonmarinated control. However, AGSP was the most effective phosphate at increasing pick-up and yields and decreasing cooking loss due to the pH effect that causes more water to be trapped within the food system. Major quality differences may not have occurred between STP and agglomerated phosphates (other than AGSP) since injection relies solely on pH and ionic strength for marinade pickup, whereas tumbling also relies on mechanical action, which relies more on the presence of various phosphate chain lengths and solubility to impact yields. All phosphate treatments improved the quality of tray-packed, refrigerated catfish fillets that were enhanced through multineedle injection. However, AGSP also increased fillet pH, optimized yields, and improved color. PRACTICAL APPLICATION Use of an agglomerated phosphate blend with a high pH (AGSP) maximized the yield of catfish fillets that were marinated through multineedle injection. In addition, STP and agglomerated phosphate blends increased the yield and tenderness of catfish fillets when compared to the nonmarinated control.

Incidence and Persistence of Listeria monocytogenes in the Catfish Processing Environment and Fresh Fillets

Incidence of Listeria spp. in whole raw catfish, catfish fillets, and processing environments from two catfish processing facilities was determined in August 2008 and August 2009. Thirty-nine (18.4%) of 212 samples collected in August 2008 were positive for Listeria monocytogenes. Prevalences of Listeria species L. innocua and L. seeligeri-L. welshimeri-L. ivanovii were 11.3 and 23.6%, respectively. Of 209 samples collected in August 2009, 12.4% were positive for L. monocytogenes, 11% for L. innocua, and 19.6% for L. seeligeri-L. welshimeri-L. ivanovii. No Listeria grayi was detected in any of the samples. L. monocytogenes was not found in catfish skins and intestines, but was detected in catfish fillets, on food contact surfaces, and on non-food contact surfaces with frequencies of 45.0, 12.0, and 11.1%, respectively. In August 2008 isolates, serotypes 1/2b (62.2%) and 3b (15.6%) were frequently isolated, whereas the majority of the August 2009 isolates (92.3%) were serotype 1/2b. Genotyping analyses revealed that some genotypes of L. monocytogenes isolates were detected in one facility even after a year, but no persistence of L. monocytogenes was observed in the other facility. In addition, some L. monocytogenes isolates from fresh fillets showed genotypes that were either identical, or more than 90% similar, to those of L. monocytogenes isolates from food contact surfaces in the processing lines. The results of this study suggest that processing environment rather than whole raw catfish is an important source of L. monocytogenes contamination in the catfish fillets. These results should assist the catfish industry to develop better control and prevention strategies for L. monocytogenes.

Effects of phosphate type on the quality of vacuum-tumbled catfish fillets.

The objective of this study was to determine the effects of various agglomerated phosphate blends on the quality of vacuum-tumbled catfish fillets. Catfish fillets were tumbled with a brine solution at 15% over initial, raw weight prior to tray-packing and storage at 4°C for 10 days. Fillets were evaluated for protein exudate, tumbling yield, color, pH, cooking loss, tenderness, purge loss, and shelf life. A specific blend of agglomerated sodium phosphates (AGSP) that contains mono-, tri-, and polyphosphates had significantly less protein (p < 0.05) exudate and significantly higher pH (p < 0.05) than other treatments. All phosphate treatments significantly increased (p < 0.05) tenderness and significantly decreased (p < 0.05) purge loss, but agglomerated phosphate blends significantly decreased (p < 0.05) cooking loss and yellowness. Psychrotrophic plate counts for all phosphate treatments were similar to the control at each storage time. All phosphate treatments improved the yield and quality of catfish fillets, but the use of AGSP may optimize quality attributes.