Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 18Citation - Scopus: 23A Thermophilic ?-L From Geobacillus Vulcani Gs90: Heterologous Expression, Biochemical Characterization, and Its Synergistic Action in Fruit Juice Enrichment(Springer, 2018) İlgü, Hüseyin; Sürmeli, Yusuf; Şanlı Mohamed, Gülşahα-l-Arabinofuranosidases with an orchestral action of xylanolytic enzymes degrades the xylan in plant cell wall. In this study, heterologous expression, biochemical characterization, and synergistic action of α-l-Arabinofuranosidase from previously identified.Geobacillus vulcani GS90 (GvAbf) was investigated. The recombinant α-l-Arabinofuranosidase was overexpressed in Escherichia coli BL21 (λDE) and purified via His-tag Ni-affinity and size-exclusion chromatography. Optimum activity of the purified α-l-Arabinofuranosidase was obtained at pH 5 and at 70 °C. The GvAbf was active in a broad pH and temperature ranges; pH 4–9 and 30–90 °C, respectively. In addition, it retained most of its activity after an hour incubation at 70 °C and remained relatively stable at pH 3–6. GvAbf was quite stable against various metal ions. The kinetic parameters of GvAbf was obtained as Vmax and Km; 200 U/mg and 0.2 mM with p-nitrophenyl-α-l-arabinofuranoside and 526 U/mg and 0.1 mM with sugar beet arabinan, respectively. The synergistic action of GvAbf was studied with commercially available xylanase on juice enrichment of apples, grapes, oranges, and peaches. The best juice enrichment in terms of clarity, reducing sugar content, and yield, was achieved with GvAbf and xylanase together compared to treatment with xylanase and GvAbf alone in all fruits. The treatment with GvAbf and xylanase together lead to an increased juice yield by 26.56% (apple), 30.88% (grape), 40.00% (orange) and 32.20% (peach) as well as having a significant effect on juice clarity by an increase of % transmittance 47.26, 25.98, 41.77, and 44.97, respectively. The highest reducing sugar level of fruit juices also obtained with GvAbf and xylanase together compared to treatment with xylanase and GvAbf alone in all types of fruits. GvAbf and xylanase together as simultaneous synergistic manner may have an exciting potential for application in fruit juice processing.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.