Publications - Refereed Journals (International)
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Infrared Assisted Microwave Cooking of Atlantic Salmon (Salmo salar)Mutlu Pilavtepe-Çelik, Nil Pembe Özer, Semin Özge Özkoç, Nadide Seyhun, Nur Dede |
ABSTRACT
In this study, infrared–microwave combination heating was used to cook Atlantic salmon (Salmo salar) samples, and the optimum cooking conditions in infrared-microwave combination oven were determined. Response Surface Methodology (RSM) was used to identify optimum values of cooking time (4, 5, 6 minutes), halogen lamp power level (80%, 90%, 100%), and microwave power level (20%, 30%, 40%) regarding of four responses – internal temperature, cooking yield, L* and b* values. A three-factors modified Box–Behnken design was carried out to estimate the model coefficients. The derived second-order polynomial models sufficiently represented the experimental data. Optimum conditions were predicted as 5 minutes of cooking time, 100% halogen lamp power level, and 30% microwave power level by using the target values obtained in conventional cooking (at 200˚C for 15 minutes). This study showed that infrared assisted microwave cooking is a promising alternative method for fish and other seafoods with reduced cooking time and color formation on the surface of salmon.
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Physiological Changes of Escherichia coli O157:H7 and Staphylococcus aureus Following Exposure to High Hydrostatic PressureMutlu Pilavtepe-Çelik, Ahmed Yousef, Hami Alpas |
ABSTRACT
Morphological changes and membrane integrity of Escherichia coli O157:H7 and Staphylococcus aureus cells before and after high hydrostatic pressure (HHP) treatments (200–400 MPa) and time (1–5 min), at a constant temperature (40 °C), in peptone water were examined by using scanning electron microscopy (SEM) and fluorescent microscopy, respectively. SEM images showed that unpressurized cells exhibited a smooth surface appearance. E. coli O157:H7 cells exposed to pressure treatments first appeared larger, then with increasing pressure distorted with dimples and pinches. In case of S. aureus, the cells pressurized at low pressure levels did not show any significant change. The surface appearance became rough and cracked when the cells were exposed to higher pressure levels. Images of fluorescent microscopy showed that a small proportion of bacterial cells were not green fluorescent at lower pressure levels. The other part of the cell population was red fluorescent representing dead cells and the number of red fluorescent cells increased with increasing pressure. The cells with a yellowish color showed that varying levels of membrane damage occurred under HHP. The combinations of mild heat, antimicrobial substances and HHP treatment can be used to inactivate food borne pathogens of varying pressure resistance in the food industry for safe processing conditions. However, the resultant damaged cells at different levels should be taken into account during storage to prevent their recovery.
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High Hydrostatic Pressure (HHP) Inactivation of Foodborne Pathogens in Low-acid JuicesMutlu Pilavtepe-Çelik |
ABSTRACT
Consumption of unpasteurised fruit/vegetable juices has increased in recent years due to their freshness, low calorie contribution and good nutritional quality. However, unpasteurised fresh juices with low acidity (pH > 4.6) and high water activity (a w > 0.85) can support the growth of pathogens. Hence, pasteurisation is a necessary process in the production of low-acid juices. Consumer demand has required minimally processed high-quality foods that are free from additives, that are fresh tasting and microbio-logically safe, and with an extended shelf life. High hydrostatic pressure (HHP) treatment is considered to be an alternative to thermal pasteurisation for fruit and vegetable juices. HHP treatment could preserve nutritional value and the sensory properties of fruits and vegetables due to its limited effect on the covalent bonds of low-molecular-mass compounds such as colour, flavour compounds and vitamins. However, inactivation of important foodborne pathogens in low-acid foods by HHP is most urgent and critical. More research should be performed in order to satisfy consumer demands for fresh-tasting products while retaining safety.
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Multi-pulsed High Hydrostatic Pressure Treatment for Inactivation and Injury of Escherichia coliMutlu Pilavtepe-Çelik, Sencer Buzrul, Hami Alpas, Alain Largeteau, Gerard Demazeau |
ABSTRACT
Escherichia coli cells in peptone water were pressurized at 300MPa at ambient temperature with no holding time (pulse series) and with a total holding duration of 300s for single- (300s×1 pulse) and multi-pulsed (150s×2 pulses, 100s×3 pulses, 75s×4 pulses, 60s×5 pulses, 50s×6 pulses and 30s×10 pulses) high hydrostatic pressure (HHP) treatments. Multi-pulsed HHP treatment with no holding time indicated that as the pulse number increased the number of inactivated and injured cells also increased. Holding time had significant effect on the inactivation of E. coli. There was low inactivation difference between single- and multi-pulsed HHP treatments with holding time. Escherichia coli cells showed at least 1.6 log10 more reduction on selective medium than the non-selective medium indicating that more than 95% of the survivors severely injured for both single- and multi-pulsed treatments with holding time. Although the inactivation difference was low between single- and multi-pulsed HHP treatments, storage at 4°C revealed that there was less recovery from injury for multi-pulsed HHP treatment.
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Development of a New Mathematical Model for Inactivation of Escherichia coli O157: H7 and Staphylococcus aureus by High Hydrostatic Pressure in Carrot Juice and Peptone WaterMutlu Pilavtepe-Çelik, Sencer Buzrul, Hami Alpas, Faruk Bozoglu |
ABSTRACT
Survival data of Escherichia coli O157:H7 933 and Staphylococcus aureus 485 in carrot juice and peptone water were collected in a range of pressure levels between 200 and 400 MPa at 40 °C. A mathematical approach combining the primary and secondary models (Weibull and first-order models as the primary model and two empirical equations as the secondary model) was proposed to estimate the microbial parameters using nonlinear least squares procedure in one step, resulting a single equation. Although not perfectly matched with the survival data, the proposed model produced good fits. Better fits were observed for S. aureus than for E. coli. Simulations of 5log10 reductions of both pathogens indicated that carrot juice had a protective effect on E. coli whereas it had a sensitizing effect on S. aureus. The development of such mathematical models would be very beneficial to the food industry by developing safe processing conditions for HHP processing of foods.
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Image Analysis Based Quantification of Bacterial Volume Change with High Hydrostatic PressureMutlu Pilavtepe-Çelik, Murat O Balaban, Hami Alpas, A.E. Yousef |
ABSTRACT
Scanning electron microscopy (SEM) images of Staphylococcus aureus 485 and Escherichia coli O157:H7 933 were taken after pressure treatments at 200 to 400 MPa. Software developed for this purpose was used to analyze SEM images and to calculate the change in view area and volume of cells. Significant increase in average cell view area and volume for S. aureus 485 was observed in response to pressure treatment at 400 MPa. Cell view area for E. coli O157:H7 933 significantly increased at 325 MPa, the maximum pressure treatment tested against this pathogen. In contrast to S. aureus, cells of E. coli O157:H7 exhibited significant increase in average view area and volume at 200 MPa. The pressure-induced increase in these parameters may be attributed to modifications in membrane properties, for example, denaturation of membrane-bound proteins and pressure-induced phase transition of membrane lipid bilayer.