Food Engineering / Gıda Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/12
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Article Citation - WoS: 17Citation - Scopus: 23Pasteurization of Verjuice by Uv-C Irradiation and Mild Heat Treatment(Wiley, 2019) Kaya, Zehra; Ünlütürk, SevcanVerjuice is a highly acidic juice and more prone to yeast spoilage. In this study, the efficacy of individual and combination processes of UV-C irradiation (UV) and mild heat treatment (MH) for pasteurization of verjuice were assessed. Saccharomyces cerevisiae (NRRL Y-139) was selected as the target microorganism and kinetic parameters for MH, UV, and combined UV + MH inactivation treatments were determined. The UV treatment alone at a UV dose of 0.57 J/cm(2) (energy of 2.30 J/mL), provided only 0.54 +/- 0.02 log CFU/mL reduction of S. cerevisiae. In contrast, the combined treatment (UV + MH2) substantially reduced the number of S. cerevisiae in verjuice, 5.16 +/- 0.24 log CFU/mL reduction was achieved at 0.25 J/cm(2) UV dose (energy of 1.01 J/mL) and 51.25 +/- 1.47 degrees C. The percentage of synergism for the UV + MH inactivation of S. cerevisiae in verjuice was maximized at 51.25 degrees C (50.79% of synergistic effect). Inactivation kinetics of S. cerevisiae was best described by Weibull model with the smallest RMSE and AIC values. D value was decreased from 13.66 to 1.94 min when UV was combined with mild heating. The results showed that UV-C light assisted by mild heat treatment can be a potential alternative to thermal pasteurization of verjuice. Practical applications Fruit juices are prone to spoilage by yeasts, molds, and some acid-tolerant bacteria. Saccharomyces cerevisiae is a heat resistant spoilage microorganism and found in some spoiled juices. Thermal pasteurization is widely used for the preservation of fruit juices but results in losses of essential nutrients and changes in physicochemical and organoleptic properties. This study illustrated that the combined UV-C light assisted by mild heat treatment can deliver the required microbial reduction in verjuice. The synergistic effect of two processing methods is suggested for controlling the growth of spoilage microflora of fruit juices.Article Citation - WoS: 21Citation - Scopus: 25Milk Fat Substitution by Microparticulated Protein in Reduced-Fat Cheese Emulsion: the Effects on Stability, Microstructure, Rheological and Sensory Properties(Korean Society for Food Science of Animal Resources, 2019) Urgu, Müge; Türk, Aylin; Ünlütürk, Sevcan; Kaymak Ertekin, Figen; Koca, NurcanFat reduction in the formulation of cheese emulsion causes problems in its flowability and functional characteristics during spray-dried cheese powder production. In order to eliminate these problems, the potential of using microparticulated whey protein (MWP) in cheese emulsions was examined in this study. Reduced-fat whitebrined cheese emulsions (RF) with different dry-matters (DM) (15%, 20%, and 25% excluding emulsifying salt) were produced using various MWP concentrations (0%-20% based on cheese DM of emulsion). Their key characteristics were compared to full-fat cheese emulsion (FF). MWP addition had no influence on prevention of the phase separation observed in the instable group (RF 15). The most notable effect of using MWP was a reduction in apparent viscosity of RF which significantly increased by fat reduction. Moreover, increasing the amount of MWP led to a decrease in the values of consistency index and an increase in the values of flow behavior index. On the other hand, using high amounts of MWP made the emulsion more liquid-like compared to full-fat counterpart. MWP utilization also resulted in similar lightness and yellowness parameters in RF as their full-fat counterparts. MWP in RF increased glossiness and flowability scores, while decreased mouth coating scores in sensory analyses. Fat reduction caused a more compact network, while a porous structure similar to FF was observed with MWP addition to RF. In conclusion, MWP showed a good potential for formulation of reducedfat cheese emulsions with rheological and sensorial characteristics suitable to be used as the feeding liquid in the spray drying process.Article Citation - WoS: 59Citation - Scopus: 71Microbial Safety and Shelf Life of Uv-C Treated Freshly Squeezed White Grape Juice(John Wiley and Sons Inc., 2015) Ünlütürk, Sevcan; Atılgan, Mehmet ReşatThe effects of UV-C irradiation on the inactivation of Escherichia coli K-12 (ATCC 25253), a surrogate of E. coli O157:H7, and on the shelf life of freshly squeezed turbid white grape juice (FSWGJ) were investigated. FSWGJ samples were processed at 0.90 mL/s for 32 min by circulating 8 times in an annular flow UV system. The UV exposure time was 244 s per cycle. The population of E. coli K-12 was reduced by 5.34 log cycles after exposure to a total UV dosage of 9.92 J/cm2 (1.24 J/cm2 per cycle) at 0.90 mL/s flow rate. The microbial shelf life of UV-C treated FSWGJ was extended up to 14 d at 4 °C. UV exposure was not found to alter pH, total soluble solid, and titratable acidity of juice. There was a significant effect (P < 0.05) on turbidity, absorbance coefficient, color, and ascorbic acid content. Furthermore, all physicochemical properties were altered during refrigerated storage. The microbial shelf life of FSWGJ was doubled after UV-C treatment, whereas the quality of juice was adversely affected similarly observed in the control samples. Practical Applications: UV-C irradiation is a non-thermal method used for processing of fruit juices with a minimal or no changes in flavor, essential nutrients, and vitamins. Fresh grape juice is a popular drink, usually consumed at summer time due to many beneficial health effects. Although thermal pasteurization is widely used for extending the shelf life of fruit juices, it causes a "cook taste" in grape juice. The applicability of UV-C irradiation as an alternative to thermal pasteurization was investigated. It is concluded that UV-C treatment can be used for extending the shelf life of fresh grape juice.Article Citation - WoS: 22Citation - Scopus: 33Uv-C Irradiation of Freshly Squeezed Grape Juice and Modeling Inactivation Kinetics(John Wiley and Sons Inc., 2014) Ünlütürk, Sevcan; Atılgan, Mehmet ReşatUV inactivation kinetics of freshly squeezed turbid white grape juice (FSTGJ) treated with an annular flow UV reactor by applying UV dosages ranging from 0 to 116.7J/mL, at three different flow rates (0.90, 1.75 and 3.70mL/s), were modeled by using log-linear, Weibull, Hom and modified Chick-Watson models. FSTGJ was circulated five times in the UV system, i.e., UV exposure time was 20.33min during processing. The populations of Escherichia coli K-12, lactic acid bacteria (LAB) and foodborne yeasts were reduced by 3.759, 4.133 and 1.604log cfu/mL, respectively, after exposure to UV dosage of 116.7J/mL at the lowest flow rate. The inactivation kinetics of foodborne yeasts were best described by the modified Chick-Watson model, with the least root mean squared error (RMSE=0.001, R2=0.999). Besides, the inactivation kinetics of E.coli K-12 and LAB were best fitted by Weibull model (R2=0.999). Additionally, when the UV exposure time was increased up to 32.5min (i.e., eight cycles), UV-C treatment of FSTGJ resulted in 5.341log cfu/mL reduction in E.coli K-12, which meets the Food and Drug Administration requirement of a 5log reduction of microorganisms in fruit juices. Practical Applications Consumer demand for high-quality fruit juice with fresh-like characteristics has markedly expanded in recent years. UV-C irradiation is a nonthermal method and allows the processing of fruit juices with a minimal or no changes in flavor, essential nutrients and vitamins. Although thermal pasteurization is the most convenient way of increasing the shelf life of fruit juices, it causes a "cook taste" in grape juice. So, in this study, the application of UV-C irradiation to process grape juice was investigated. The shape of the microbial inactivation curve is sigmoidal in UV treatment. Therefore, different kinetic models (e.g., log-linear, Weibull, Hom and modified Chick-Watson) are applied to describe the inactivation kinetics of Escherichia coli K-12, lactic acid bacteria and foodborne yeasts. Kinetic parameters (e.g., k and D) and models can be used for the development of UV-C irradiation process to ensure microbial safety in juice products.Article Citation - WoS: 1Citation - Scopus: 2Discrimination of Bio-Crystallogram Images Using Neural Networks(Springer Verlag, 2014) Ünlütürk, Sevcan; Ünlütürk, Mehmet S.; Pazır, Fikret; Kuşçu, AlperThis study utilized a unique neural network model for texture image analysis to differentiate the crystallograms from pairs of fresh red pepper fruits from conventional and organic farms. The differences in visually analyzed samples are defined as the distribution of crystals on the circular glass underlay, the thin or thick structure of crystal needles, the angles between branches and side needles, etc. However, the visual description and definition of bio-crystallogram images has major disadvantages. A novel methodology called an image neural network (INN) has been developed to overcome these shortcomings. The 1,488 × 2,240 pixel bio-crystallogram images were acquired in a lab and cropped to 425 × 1,025 pixel images. These depicted either a conventional sweet red pepper or an organic sweet red pepper. A set of 19 images was utilized to train the image neural network. A new set of 4 images was then prepared to test the INN performance. Overall, the INN achieved an average recognition performance of 100 %. This high level of recognition suggests that the INN is a promising method for the discrimination of bio-crystallogram images. In addition, Hinton diagrams were utilized to display the optimality of the INN weights.Article Citation - WoS: 38Citation - Scopus: 48The Impact of Uv-C Irradiation on Spoilage Microorganisms and Colour of Orange Juice(Springer Verlag, 2013) Hakgüder Taze, Bengi; Ünlütürk, Sevcan; Buzrul, Sencer; Alpas, HamiThe effect of UV-C irradiation on inactivation of spoilage microorganisms and colour of freshly squeezed orange juice were investigated. Orange juice samples were intentionally fermented in order to increase the natural microflora which were mostly composed of yeasts and then exposed to UV-C irradiation at an intensity level of 1.32 mW/cm2 and sample depth of 0.153 cm for several exposure times by using a collimated beam apparatus. Applied UV dose was in the range of 0 and 108.42 mJ/cm2. Resistance of yeast to UV light and existence of suspended particles limited the effectiveness of the process. Survival data obtained for yeasts was either described by the Weibull or traditional first-order model and goodness-of-fit of these models was investigated. Weibull model produced a better fit to the data with higher adjusted determination coefficient (R2 adj) and lower mean square error (MSE) values which were 0.99 and 0.003, respectively. Time and UV dose of first decimal reduction were obtained as 5.7 min and 31 mJ/cm2, respectively. The data suggests that biodosimetric studies performed by using inoculated microorganisms for assesment of the efficiency of UV irradiation treatment in the shelf life extension of juices must be carefully evaluated. UV-C irradiation had no influence on the colour of orange juice.Article Citation - WoS: 12Citation - Scopus: 13The Discrimination of Raw and Uht Milk Samples Contaminated With Penicillin G and Ampicillin Using Image Processing Neural Network and Biocrystallization Methods(Academic Press Inc., 2013) Ünlütürk, Sevcan; Pelvan, Merve; Ünlütürk, Mehmet S.This paper utilized a neural network for texture image analysis to differentiate between milk, either raw or ultra high temperature (UHT) with antibiotic residues (e.g., penicillin G and ampicillin) and milk without antibiotic residues. The biocrystallization method was applied to obtain biocrystallogram images for milk samples spiked with penicillin G and ampicillin at different concentration levels. The biocrystallogram images were used as an input for a designed neural network called the image processing neural network (ImgProcNN). The visual differences in these images that were based on textural properties, including the distribution of crystals on the circular grass underlay, the thin or thick structure of the crystal needles, and the angles between the branches and the side needles, were used to discriminate the antibiotic-free milk samples from samples with antibiotic residues. The visual description and definition of these images have major disadvantages. In this study, the ImgProcNN was developed to overcome the shortcomings of these visual descriptions and definitions. Overall, the neural network achieved an average recognition performance between 86% and 100%. This high level of recognition suggests that the neural network used in this paper has potential as a method for discriminating raw and UHT milk samples contaminated with different antibiotics.Article Citation - WoS: 51Citation - Scopus: 58Rheological Properties of Liquid Egg Products (leps)(Taylor and Francis Ltd., 2008) Atılgan, Mehmet Reşat; Ünlütürk, SevcanRheological properties were determined at 4°C (refrigerated temperature), 25°C (room temperature), 60°C (pasteurization temperature) for liquid whole egg (LWE) and liquid egg yolk (LEY) and 4, 25, 55.6°C for liquid egg white (LEW) by using concentric cylinder viscometer. The shear rate range was 8 to 53.7 s-1 for LEW and LWE, and 1 to 34 s-1 for LEY. Selected physical properties (e.g., density) of LEPs were studied at broad range of temperatures from 4°C to 60°C. All liquid egg products (LEPs) exhibited mildly shear thinning (pseudoplastic) behavior. Experimental data of LWE and LEW successfully fitted Herschel-Bulkley model, LEY data were well described by power law model. LEW and LWE showed thixotropy and time-dependency at their pasteurization temperatures (55.6°C for LEW, 60°C for LWE) and considered being time-independent below these temperatures. LEY exhibited time-dependent behavior at 4°C and 60°C. But its rheological behavior showed no thixotropy and time-dependency at room temperature. The density of all three products decreased with increasing temperature. Density data were correlated by polynomial models (r2 > 0.99).Article Citation - WoS: 8Citation - Scopus: 8Differential Scanning Calorimetry as a Tool To Detect Antibiotic Residues in Ultra High Temperature Whole Milk(John Wiley and Sons Inc., 2009) Yıldız, Özge; Ünlütürk, SevcanDetection of penicillin G, ampicillin and tetracycline in ultra high temperature whole milk was studied by differential scanning calorimetry (DSC). Thermal parameters including the heat of fusion, the evaporation temperature, the heat of evaporation and the melting temperature obtained from DSC analysis were used to characterise thermal behaviour of antibiotic free milk samples and milk samples fortified with Penicillin G, Ampicillin and Tetracycline. DSC curves of these antibiotics at selected concentrations (0, 2, 4, 8 ppb for Penicillin G and Ampicillin; 0, 100, 250, 500 ppb for Tetracycline) show big endothermic peaks in the temperature range of -30 °C and 200 °C. It was concluded that the antibiotic concentration had a significant effect on the thermal parameters at a 95% confidence level. The differences between the melting temperatures and the peak areas in heat flow curves provided a basis for detection of antibiotic residues in UHT whole milk.Article Citation - WoS: 33Citation - Scopus: 37Relationship Between Morphology, Rheology and Polygalacturonase Production by Aspergillus Sojae Atcc 20235 in Submerged Cultures(Elsevier Ltd., 2006) Göğüş, Nihan; Tarı, Canan; Öncü, Şelale; Ünlütürk, Sevcan; Tokatlı, FigenA full factorial statistical design, with the factors of, two taxonomically different strains, seven types of seed culture formulations (slants) and two types of fermentation media were used to investigate the effect of these parameters on the morphology and polygalacturonase production. The rheology of the final fermentation medium was analyzed and appropriate mathematical model was applied to calculate suspension viscosity. It was found that most fermentation broths showed non-Newtonian flow behavior. According to statistical analysis, factors of strain types and fermentation media and the interaction between them were found significant on the enzyme activity. The effect of seed culture formulations (slants) were found insignificant at the significance level of 1%. Interaction of slants with strain types and fermentation media were also found insignificant. Considering the morphology of the final culture, Aspergillus sojae with the desired pellet morphology in a complex media, inoculated with a seed culture prepared from molasses resulted in maximum polygalacturonase enzyme activity (0.2 U/ml) and lowest suspension viscosity with a broth rheology close to Newtonian flow behavior.