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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 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 Evaluation of heat seal quality of aseptic food containers by ultrasonic and optical microscopic imaging(Springer-Verlag, 2003) Ayhan, Z; Zhang, QHNon-destructive testing by the ultrasonic imaging method was evaluated to determine the heat seal quality of aseptically produced semi rigid cups, sealed at temperatures ranging from 150 to 200 degreesC. Non-contact ultrasonic testing in pulse/echo mode using high frequency sound waves generated by a 20 MHz ultrasonic transducer was used to evaluate heat-seal quality. In order to relate ultrasonic response with the actual seal condition, various seal regions of a semi rigid container were sectioned for optical microscopic imaging and seal characterization. Results showed that ultrasonic signals could reflect the effects of the sealing process on the seal integrity. Change in the ultrasonic signals indicated an insufficient or non-uniform heat seal at sealing temperatures of 150-170 degreesC, resulting in weak seals or discontinuities. Short seal width was observed at all sealing temperatures, indicating unparallel alignment of the sealing tool. Optical imaging correlated well with ultrasonic imaging. However, uniformity of heat seal did not correlate well with the magnitude of the ultrasonic signal, possibly due to non-uniform surfaces of heat seals. These results suggest that this non-destructive ultrasonic inspection system detects the quality of heat seals, which can eliminate potential failures and improve process control.Öğe Flavor, color, and vitamin C retention of pulsed electric field processed orange juice in different packaging materials(Amer Chemical Soc, 2001) Ayhan, Z; Yeom, HW; Zhang, QH; Min, DBEffects of packaging materials, storage temperature, and time on the stability of pulsed electric field (PEF) processed orange juice were investigated. Single-strength orange juice was treated with PEF at an electric field strength of 35 kV/cm for 59 mus using an integrated pilot plant scale PEF processing and glovebox packaging system. The retention of eight orange juice aroma compounds, color, and vitamin C in glass, polyethylene terephthalate (PET), high-density polyethylene, and low-density polyethylene were evaluated at 4 and 22 degreesC for 112 days; Packaging material had a significant effect (p less than or equal to 0.05) on the retention of orange juice aroma compounds, color, and vitamin C. PEF-treated orange juice had a shelf life of >16 weeks in glass and PET at 4 degreesC.Öğe Inspection of seal integrity of food packages using ultrasound and pressure differential techniques(Amer Soc Agricultural & Biological Engineers, 2001) Ayhan, Z; Zhang, QH; Farahbakhsh, B; Kneller, MFood packages undergo incubation and inspection to ensure that packages are sealed tight and protect the food from contamination and spoilage. Over the years many inspection techniques are used with varying degrees of success. With this study, two techniques, ultrasound and pressure differential technique, were assessed and the effectiveness of these techniques was quantified. Non-contact, immersion type ultrasonic testing in pulse/echo mode using high frequency sound waves was evaluated for use in defect detection in the seal area of semi-rigid cups and polymeric trays. At disparities within the seal, sound waves generated by 20-MHz ultrasonic transducer were reflected back to the receiver. Received ultrasonic signals, or echoes, were used to develop A-scan and C-scan presentations. Discontinuities in the seal, short seal, non-bonded areas, imbedded foreign matter such as wire and Teflon in the seal, contaminated seal, and abrasion were detected using ultrasound based on reduced signal strengths. Integrity of meals-ready-to-eat (MRE) pouches was inspected using a new pressure (vacuum) differential technique. This technique is based on a three-step approach. To evaluate the system, air was linked into a test chamber through a calibrated needle valve simulating a leak at different leak rates. A simulated leak that generated values higher than reference, and dependant upon the leak rate, was accepted or rejected by the leak tester The technique proved to be effective, although, short-sealed non-vacuum packed pound cake pouches failed during subsequent leak testing.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).
