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Öğe Application of pulsed electric fields to skim milk inoculated with Staphylococcus aureus(Academic Press Inc Elsevier Science, 2004) Evrendilek, GA; Zhang, QH; Richter, ERApplication of pulsed electric fields (PEF) to skim milk inoculated with Staphylococcus aureus was conducted in the study. Skim milk samples were treated by PEF, using fluid handling systems of both circulation and stepwise modes. Parameters for the PEF were 3.7 mus pulse duration time, 250 Hz pulse repetition rate, 1 ml s(-1) flow rate, 460 mus total treatment time, and 3.5 kV mm(-1) electric field strength. After the PEF-treatment, the samples were plated onto both tryptic soya agar and Baird Parker agar with egg yolk tellurite enrichment to enumerate the number of inactivated and injured cells. Survivals of PEF-treated S. aureus cells were also enumerated at refrigeration temperature for 2 weeks. There was a significant decrease in S. aureus cells caused by the two fluid handling systems (probability P < 0.05). The difference in the inactivation due to the PEF treatment with the fluid handling systems was not significant (P > 0.05). After the PEF treatment, there was no significant injury of the PEF-treated cells (P > 0.05). Relative to the control samples, there was a significant reduction in the number of the PEF-treated cells at 4degreesC for 2 weeks (P < 0.05). (C) 2003 Silsoe Research Institute. All rights reserved Published by Elsevier Ltd.Öğe Chemical compositions and antibacterial effects of essential oils of Turkish oregano (Origanum minutiflorum), bay laurel (Laurus nobilis), Spanish lavender (Lavandula stoechas L.), and fennel (Foeniculum vulgare) on common foodborne pathogens(Amer Chemical Soc, 2004) Dadalioglu, I; Evrendilek, GAChemical compositions and inhibitory effects of essential oils of Turkish oregano (Origanum minutiflorum O. Schwarz & P. H. Davis), bay laurel (Laurus nobilis L.), Spanish lavender (Lavandula stoechas subsp. stoechas L.), and fennel (Foeniculum vulgare Mill.) on Escherichia coli O157:H7, Listeria monocytogenes, Salmonella typhimurium, and Staphylococcus aureus were determined. After the essential oils were applied on the foodborne pathogens at doses of 0 (control), 5, 10, 20, 30, 40, 50, and 80 muL/mL, the resultant numbers of cells surviving were counted. Results revealed that all essential oils exhibited a very strong antibacterial activity against the tested bacteria (P < 0.05). Gas chromatography-mass spectrophotometry analyses revealed that carvacrol (68.23%), 1,8-cineole (60.72%), fenchone (55.79%), and trans-anethole (85.63%) were the predominant constituents in Turkish oregano, bay laurel, Spanish lavender, and fennel essential oils, respectively.Öğe Effects of pH, temperature, and pre-pulsed electric field treatment on pulsed electric field and heat inactivation of Escherichia coli O157:H7(Int Assoc Food Protection, 2003) Evrendilek, GA; Zhang, QHThis investigation was undertaken to study the inactivation of Escherichia coli O157:H7 by pulsed electric field (PEF) treatment and heat treatment after exposure to different stresses. E. coli O157:H7 cells exposed to different pHs (3.6, 5.2, and 7.0 for 6 h), different temperatures (4, 35, and 40degreesC for 6 h), and different pre-PEF treatments (10, 15, and 20 kV/cm) were treated with PEFs (20, 25, and 30 kV/cm) or heat (60degreesC for 3 min). The results of these experiments demonstrated that a pH of 3.6 and temperatures of 4 and 40degreesC caused significant decreases in the inactivation of E. coli O157:H7 by PEF treatment and heat treatment (P < 0.05). Pre-PEF treatments, pHs of 5.2 and 7.0, and a temperature of 35degreesC, on the other hand,did not result in any resistance of E. coli O157:H7 cells to inactivation by PEF treatment and heat treatment (P > 0.05).Öğe Effects of pulse polarity and pulse delaying time on pulsed electric fields-induced pasteurization of E. coli O157:H7(Elsevier Sci Ltd, 2005) Evrendilek, GA; Zhang, QHEffects of pulse polarity and pulse delaying time on inactivation of E. coli O157:H7 inoculated into apple juice and skim milk samples were determined. Inactivation effect was observed as inoculated food samples were subjected to mono and bipolar square wave pulses. Bipolar pulses with different pulse delaying times were also applied. There was no significant difference between mono (2.56 log(10) cfu/ml) and bipolar (2.63 log(10) cfu/ml) pulses on the inactivation of E. coli O157:H7 inoculated into apple juice (P > 0.05). However. results in skim milk yielded a significant difference between mono (1.27 log(10) cfu/ml) and bipolar (1.96 log(10) cfu/ml) pulses with bipolar pulses being significantly more efficient (P < 0.05). Among different pulse delaying times, 20 mus caused a significantly higher inactivation than the others (P < 0.05) in apple juice and skim milk. (C) 2004 Elsevier Ltd. All rights reserved.Öğe Isolation and characterization of verocytotoxin-producing Escherichia coli O157 from Turkish cattle(Elsevier, 2006) Aslantas, Ö; Erdogan, S; Cantekin, Z; Gülaçti, I; Evrendilek, GAThe objective of this study was to collect rectal swabs from the cattle in a slaughterhouse located in Hatay (Turkey) immediately after slaughter for the isolation and characterization of verotoxin-producing Escherichia coli O157 in each month during a 1-year period. The rectal swab samples were analyzed for the isolation of E. coli O157 through preenrichment, immunomagnetic separation and selective plating on CT-SMAC agar. E. coli O157 was isolated from 77 (13.6%) of the samples. The presence of E. coli O157 changed during a 1-year period, in that the occurrence of E. coli O157 was the highest in July and November and lowest in February. A total of 66 isolates out of 77 were seroytpe O157:H7 and 11 were serotype O157:NM. PCR analysis of E. coli O157 virulence genes revealed that all O157:H7/NM were positive for rbf(O157), 74 positive for EhlyA, 72 positive for eaeA, 62 positive for vtx2, and 3 positive for both vtx1 and vtx2. It was presented by cytotoxicity tests that many of E. coli O157 isolates showed high cytotoxicity on Vero cells. All of the isolates containing EhlyA showed enterohaemolysin production. (c) 2005 Elsevier B.V. All rights reserved.Öğe Processing of yogurt-based products with pulsed electric fields: Microbial, sensory and physical evaluations(Wiley, 2004) Yeom, HW; Evrendilek, GA; Jin, ZT; Zhang, QHYogurt-based products similar to a dairy pudding dessert were formulated and processed by mild heat and pulsed electric fields (PEF) to investigate the effects of combined mild heat and PEF treatment on the microbial stability and quality of high viscosity foods. Commercial plain low fat yogurt was mixed with fruit jelly and corn syrup and processed by mild heat treatment at 60C for 30 s and 30 kV/cm electric field strength for 32 mus total treatment time using OSU-2C pilot plant scale PEF system. Control and processed products were aseptically packaged and stored at 4 and 22C. Mild heat combined with PEF treatment significantly decreased the total viable aerobic bacteria and total mold and yeast of yogurt-based products during storage at both 4 and 22C (P less than or equal to 0.05). Mild heat treatment alone without any PEF treatment did not prevent the growth of microorganisms in yogurt-based products. Sensory evaluation indicated that there was no significant difference between the control and processed products (P :5 0.05). Color, pH and degreesBrix were not significantly affected by mild heat and PEF processing conditions.Öğe Pulsed electric field processing of beer: Microbial, sensory, and quality analyses(Wiley, 2004) Evrendilek, GA; Li, S; Dantzer, WR; Zhang, QHIn this study, pulsed electric field (PEF) treatment of beer, effectiveness of PEF treatment on microbial inactivation, effects of PEF treatment on sensory properties, and detection of electrode material migration were explored. Beer samples were treated by PEF for the inactivation of natural flora and inoculated cultures of Saccaromyces uvarum, Rhodotorula rubra, Lactobacillus plantarum, Pediococcus damnosus, and Bacillus subtilis. Inactivation induced by the PEF treatment was 0.5, 4.1, 4.3, 4.7, 5.8, and 4.8 log(10) colony-forming units/mL in the above microorganisms, respectively (P < 0.05). There was a significant increase in the amount of Cr, Zn, Fe, and Mn ions in the beer samples after PEF treatment (P < 0.05) leading to a statistically significant degradation in flavor and mouth feel. Further studies are needed to optimize electrode materials and PEF treatment to minimize or eliminate this degradation.Öğe Pulsed electric field treatment of liquid whole egg inoculated with Salmonella enteritidis(Wiley, 2004) Hermawan, N; Evrendilek, GA; Dantzer, WR; Zhang, QH; Richter, ERThe effects of pulsed electric fields (PEF) on the inactivation of Salmonella Enteritidis inoculated into liquid whole egg (LWE) and on the physical properties and the shelf-life of LWE were studied. PEF processing conditions were 1.2 mL/s flow rate, 200 pps frequency, 2.12 mus pulse duration, 25 kV/cm electric field strength, and 250 lis total treatment time. The PEF processing caused up to 1 log(10) cfu/mL reduction in S. Enteritidis population in LWE. The PEF-treated samples were subjected to heat at 55C for 3.5 min to inactivate the remaining bacteria without denaturing the LWE. ne combination of PEF and heat treatments led to a 4.3 log(10) cfu/mL reduction in S. Enteritidis population (P < 0.05) and caused no significant change in viscosity, electrical conductivity, color, pH, and degreesBrix, relative to control samples (P > 0.05). The PEF+55C treated LWE samples presented significantly longer shelf-life at 4C compared with the control and heat treated samples (P < 0.05).Öğe Safety and quality evaluation of a yogurt-based drink processed by a pilot plant pef system(Wiley, 2004) Evrendilek, GA; Yeom, HW; Jin, ZT; Zhang, QHYogurt-based drink samples were prepared by mixing plain yogurt, water, sugar, and strawberry flavored fruit syrup. The samples were treated by both the mild heat (60C for 30 s) combined with a pilot plant pulsed electric field (PEF) system and the mild heat only in order to determine changes in the product safety and quality. Changes in the product safety were measured as microbial count, and changes in the product quality as L, a, b, degreesBrix and pH values. The treated and control samples were stored at 4 and 22C for microbial, physical and sensory evaluations. Since the 60C-treated samples exploded after 14-day storage, the safety and quality evaluations for 91 days were performed for the 60C+PEF and control samples, only. Microbial count of the 60C+PEF samples was significantly lower than that of the control samples at the two temperatures for the 91-day storage (P < 0.05). There was no significant difference in the L, a, b values, degreesBrix and pH between the control and 60C+PEF samples (P < 0.05). The control and 60C+PEF samples revealed no significant difference in the selected sensory attributes (P < 0.05).
