Food Engineering / Gıda Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/12
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Article Citation - WoS: 24Citation - Scopus: 25Investigation of the Structure of Alpha-Lactalbumin Protein Nanotubes Using Optical Spectroscopy(Cambridge University Press, 2014) Tarhan, Özgür; Tarhan, Enver; Harsa, ŞebnemAlpha-lactalbumin (α-la) is one of the major proteins in whey. When partially hydrolysed with Bacillus licheniformis protease, it produces nanotubular structures in the presence of calcium ions by a self-assembly process. This study presents investigation of α-la protein structure during hydrolysis and nanotube formation using optical spectroscopy. Before spectroscopic measurements, nanotubes were examined with microscopy. The observed α-la nanotubes (α-LaNTs) were in the form of regular hollo strands with a diameter of about 20 nm and the average length of 1 μm. Amide and backbone vibration bands of the Raman spectra displayed remarkable conformational changes in α and β domains in the protein structure during nanotube growth. This was confirmed by the Fourier-transform infrared (FTIR) spectroscopy data. Also, FTIR analysis revealed certain bands at calcium (Ca++) binding sites of COO- groups in hydrolysed protein. These sites might be critical in nanotube elongation.Article Citation - WoS: 13Citation - Scopus: 14Nanotubular Structures Developed From Whey-Based ?-Lactalbumin Fractions for Food Applications(John Wiley and Sons Inc., 2014) Tarhan, Özgür; Harsa, ŞebnemWhey proteins have high nutritional value providing use in dietary purposes and improvement of technological properties in processed foods. Functionality of the whey-based α-lactalbumin (α-La) may be increased when assembled in the form of nanotubes, promising novel potential applications subject to investigation. The purpose of this study was to extract highly pure α-La from whey protein isolate (WPI) and whey powder (WP) and to construct protein nanotubes from them for industrial applications. For protein fractionation, WPI was directly fed to chromatography, however, WP was first subjected to membrane filtration and the retentate fraction, whey protein concentrate (WPC), was obtained and then used for chromatographic separation. α-La and, additionally β-Lg, were purified at the same batches with the purities in the range of 95%-99%. After enzymatic hydrolysis, WPI-based α-La produced chain-like and long nanotubules with ∼20 nm width while WPC-based α-La produced thinner, miscellaneous, and fibril-like nanostructures by self-assembly. Raman and FT-IR spectroscopies revealed that α-La fractions, obtained from both sources and the nanostructures, developed using both fractions have some structural differences due to conformation of secondary structure elements. Nanotube formation induced gelation and nanotubular gel network entrapped a colorant uniformly with a transparent appearance. Dairy-based α-La protein nanotubules could be served as alternative gelling agents and the carriers of natural colorants in various food processes.Article Citation - WoS: 39Citation - Scopus: 49Prevalence and Antibiotic Resistance of Foodborne Staphylococcus Aureus Isolates in Turkey(Mary Ann Liebert Inc., 2011) Aydın, Ali; Muratoğlu, Karlo; Sudağıdan, Mert; Bostan, Kamil; Okuklu, Burcu; Harsa, ŞebnemIn this study, 154 Staphylococcus aureus isolates were detected from 1070 food samples (14.4%) collected from seven cities in Turkey. Antimicrobial susceptibility testing against 21 antibiotics was performed by agar disk diffusion method, and those isolates resistant to any antibiotic were further analyzed to determine minimum inhibitory concentration by E-test and polymerase chain reaction analysis of vanA and mecA genes. According to disk diffusion test results, a total of 139 strains were resistant to at least one tested antibiotic, with 39 (25.3%) strains being multidrug resistant (MDR) and the other 15 strains being susceptible to all antibiotics. Penicillin G, linezolid, erythromycin, and tetracycline took up 71.4%, 23.4%, 18.2%, and 15.6% of the tested strains, respectively. In addition, all of the strains were susceptible to vancomycin, oxacillin, cefoxitin, and imipenem. Only one strain (S158B) was resistant to both teicoplanin and cefazolin. On the other hand, the presence of vanA and mecA genes was not detected in the strains. Pulsed-field gel electrophoresis analysis was used to identify genetic-relatedness of the MDR strains. It is noteworthy that some strains from different sources showed 100% homology; however, some of MDR strains were found unrelated with 60% or less homology. The high diversity observed in pulsed-field gel electrophoresis results indicated the possible contamination of S. aureus from different sources and routes.