Letter to the Editor: Effects of Omega-3 Fatty Acids on Erectile Dysfunction in a Rat Model of Atherosclerosis-induced Chronic Pelvic Ischemia

Emin Özbek 대한의학회 2017 Journal of Korean medical science Vol.32 No.12

A modelling study on hydrolysis of whey lactose and stability of β-galactosidase

Belma Özbek,Elçin Demirhan,Dilek K l ç Apar 한국화학공학회 2010 Korean Journal of Chemical Engineering Vol.27 No.2

In the present study, the effect of process conditions on whey lactose hydrolysis and enzyme inactivation were investigated. The experiments were carried out in 250 mL of 25 mM phosphate buffer solution by using β-galactosidase produced from Kluyveromyces marxianus lactis in a batch reactor system. The degree of lactose hydrolysis (%) and residual enzyme activity (%) against time were investigated versus lactose concentration, enzyme concentration,temperature and pH. The mathematical models were derived from the experimental data to show the effect of process conditions on lactose hydrolysis and residual enzyme activity (in the presence and absence of lactose). At the optimum process conditions obtained (50 g/L of lactose concentration, 1 mL/L of enzyme concentration, 37 oC of temperature and pH 6.5), 81% of lactose was hydrolyzed and enzyme lost its activity by 32%. The activation energy for hydrolysis reaction (EA) and the enzymatic inactivation energy (ED) were calculated as 52.7 kJ/mol and 96.7 kJ/mol. Mathematical models at various process conditions have been confirmed with the experimental results.

Preparation and characterization of polymer-coated mesoporous silica nanoparticles and their application in Subtilisin immobilization

Belma Özbek,Şule Ünal 한국화학공학회 2017 Korean Journal of Chemical Engineering Vol.34 No.7

The preparation and characterization of polymer-coated mesoporous silica nanoparticles (MSNs) and their application in Subtilisin (Alcalase®) immobilization were investigated. For the synthesis of polymer-coated MSNs, acrylic acid (AA) and chitosan (CS) mixture were blended as poly(acrylic acid) (PAA) and CS polymer layer onto MSNs via in-situ polymerization technique. Then, both uncoated MSNs and polymer-coated mesoporous silica nanoparticles (CS-PAA/MSNs) were characterized by taking into account properties such as morphologic pattern, size distribution, surface charge of the particles as well as thermogravimetric stability with SEM, TEM, Zetasizer and TGA analyses. Subtilisin was immobilized onto polymer-coated mesoporous silica nanoparticles via adsorption technique. For optimizing the enzyme immobilization process, the percent enzyme loading depending on the matrix amount, immobilization time and pH were investigated. Then, the activity values of immobilized enzyme and free enzyme were compared at various pH and temperature values. The maximum enzyme activity was achieved at pH 9.0 for both immobilized and free enzyme. Immobilized enzyme showed more stability at higher temperatures compared with free enzyme. Furthermore, the operational and storage stability of immobilized enzyme were determined. The activity of immobilized enzyme was reduced from 100% to 45.83% after five repeated uses. The storage stability of immobilized enzyme was found to be higher than that of free enzyme. The activity of immobilized enzyme was reduced from 100% to 60% after 28 days of storage time. We concluded that the polymer-coated MSNs were a suitable matrix for Subtilisin immobilization compared to uncoated MSNs.

Sesame cake protein hydrolysis by alcalase: Effects of process parameters on hydrolysis, solubilisation, and enzyme inactivation

Elçin Demirhan,Belma Özbek,Dilek K l ç Apar 한국화학공학회 2011 Korean Journal of Chemical Engineering Vol.28 No.1

We investigated the effects of process parameters (substrate concentration, enzyme concentration, temperature and pH) on the hydrolysis and solubilization of sesame cake protein as well as enzyme stability. The sesame cake protein was hydrolyzed by Alcalase enzyme (a bacterial protease produced by a selected strain of Bacillus Licheniformis)that was chosen among five commercial enzymes examined. The optimum process conditions for hydrolysis and solubilization were obtained as 15 g L^(−1) substrate concentration, 3 ml L^(−1) enzyme concentration, 50 ℃ and pH 8.5. Under these conditions, the values of degree of hydrolysis and solubilization were found as 26.3% and 82.1%, respectively,and enzyme lost its activity by approx. 56% at the end of 120 min processing time. Modeling studies were performed to determine the kinetics of hydrolysis, solubilization and enzyme inactivation. The relationship between hydrolysis and solubilization was found linear for all experimental conditions examined. The inactivation energy of Alcalase at the temperature range of 45-55 ℃ was determined to be 25544 J mol^(−1).

Drying kinetics and effective moisture diffusivity of purslane undergoing microwave heat treatment

Elçin Demirhan,Belma Özbek 한국화학공학회 2010 Korean Journal of Chemical Engineering Vol.27 No.5

The effects of microwave drying on moisture content, moisture ratio, drying time and effective moisture diffusivity of purslane leaves (Portulaca oleracea L.) were investigated. By increasing the microwave output power (180-900W) and the sample amounts (25-100 g), the drying time decreased from 43 to 12.5 minutes and increased from 27 to 54 minutes, respectively. To determine the kinetic parameters, the drying data were fitted to various models based on the ratios of the differences between the initial and final moisture contents and equilibrium moisture content versus drying time. Among the models proposed, the semi-empirical Midilli et al. model gave a better fit for all drying conditions applied. By increasing the microwave output power and decreasing the sample amount, the effective moisture diffusivity values ranged from 5.913×10−11 to 1.872×10−10 m2/s and from 9.889×10−11 to 3.292×10−11 m2/s, respectively. The activation energy was calculated using an exponential expression based on the Arrhenius equation.

Acute Necrotizing Pancreatitis and Coronavirus Disease-2019 (COVID-19)

( Ulaş Aday ),( Ercan Gedik ),( Mehmet Tolga Kafadar ),( Erdal Özbek ) 대한소화기학회 2021 대한소화기학회지 Vol.78 No.6

Coronavirus disease-19 (COVID-19) is caused by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV- 2) and has resulted in increased mortality worldwide. Several studies have identified the involvement of the gastrointestinal tract, respiratory tract, and other tissues. Although it has been reported that the angiotensin-converting enzyme-2 receptor affected by SARS-CoV is expressed more in the pancreas than in the lungs, the issue regarding the occurrence of pancreatitis is controversial. SARS Cov-2 rarely causes acute necrotizing pancreatitis without significantly affecting the respiratory and other systems. This paper presents a patient who underwent laparotomy due to acute necrotizing pancreatitis and hemodynamic instability caused by COVID-19 without any known risk factors. (Korean J Gastroenterol 2021;78:353-358)

Hybrid Magnetic‑Piezoelectric Energy Harvester for Power Generation around Waistline During Gait

Mustafa İlker Beyaz,Fatih Tat,Kamil Yunus Özkaya,Ramazan Özbek 대한전기학회 2020 Journal of Electrical Engineering & Technology Vol.15 No.1

The development of a novel hybrid energy harvester for scavenging power around human waistline is presented. The harvester is composed of mm-scale electromagnetic coils and piezoelectric transducers incorporated on a belt, as well as permanent magnet structures placed on wristbands. The coils and transducers are positioned on the belt such that they correspond to either sides of the waist, facing the wrists and the hipbone. This confguration leads to simultaneous power generation on the coils and transducers due to swinging arm motion and varying belt stress during gait, respectively. Moderate walking at 1 m/s resulted in a peak open circuit voltage of 2.8 V on the coils, reaching up to 4.3 V at 2 m/s fast walking. The open circuit voltage obtained from the transducers varied from 5.2 to 9 V, corresponding to moderate walking at 1 m/s and running at a speed of 3 m/s, respectively. Instantaneous AC power was characterized separately at 1 m/s walking speed, and measured to be 14 mW and 13.5 μW from the coils and piezoelectric transducers, respectively. The two harvesting mechanisms were coupled with rectifers and DC/DC converter circuitry to store energy in an onboard 20 mAh 3 V LiPo battery. Walking for 10 min was shown to raise the battery voltage from 2.2 to 2.8 V. The results reported here demonstrate the feasibility of this MEMS-scale harvesting scheme to recharge batteries of portable electronic devices.

Influence of Vitamin (B1, B6, B9, B12, C) and Ions (Cu2+, Mn2+, PO4 3−) on Kefir Grain Biomass Growth

Elçin Demirhan,Büşra Gürses,Bengi Ece Yalçin,Dilek Kiliç Apar,Belma Özbek 한국식품과학회 2013 Food Science and Biotechnology Vol.22 No.4

The aim of the present study was to investigate the effects of additions of various vitamins (B1, B6, B9, B12,and C) and minerals (CuSO4·H2O, MnSO4·H2O, and Na3PO4·12 H2O) on the propagation of kefir grains. The activated kefir grains were inoculated into very low fat (0.1%) cows’ milk under constant temperature (25oC) and impeller speed (100 rpm) for a propagation time of 24 h. After evaluation of the experimental data, the most influential mineral addition providing 39% increase of kefir grain biomass was found to be Na3PO4·12 H2O with a concentration of 0.30 g phosphate (PO43−) ion/L. At this optimal condition, a model was also derived for the kefir grain biomass concentration representing pH dependence. This study demonstrated the basis for further research in the direction of kefir grain biomass growth considering the effect of additions of vitamins and minerals to other researchers working in the same field and to dairy industry as well.

Hepatic and splenic sonographic and sonoelastographic findings in pulmonary arterial hypertension

İlhan Hekimsoy,Burçin Kibar Öztürk,Hatice Soner Kemal,Meral Kayıkçıoğlu,Ömer Faruk Dadaş,Gülgün Kavukçu,Mehmet Nurullah Orman,Sanem Nalbantgil,Sadık Tamsel,Hakan Kültürsay,Süha Süreyya Özbek 대한초음파의학회 2021 ULTRASONOGRAPHY Vol.40 No.2

Purpose: The aim of this study was to evaluate the associations of sonographic and sonoelastographic parameters with clinical cardiac parameters, as well as to assess their value in predicting survival in patients with pulmonary arterial hypertension (PAH). Methods: Thirty-six patients with PAH and normal liver function were prospectively enrolled in this prospective study along with 26 healthy controls, all of whom underwent ultrasound and point shear wave elastography examinations. Additionally, the portal vein pulsatility index (PVPI), inferior vena cava collapsibility index, and clinical cardiac variables were obtained in PAH patients. The values of hepatic (LVs) and splenic shear wave velocity (SVs) were compared between PAH patients and controls. The relationships between all sonographic and clinical parameters in the PAH patients were analyzed. Furthermore, their prognostic value in predicting survival was investigated. Results: LVs values in PAH patients (median, 1.62 m/s) were significantly higher than in controls (median, 0.99 m/s), while no significant difference was observed in SVs values. Patients with higher grades of tricuspid regurgitation (TR) had significantly different values of PVPI (P=0.010) and sonoelastographic parameters (P<0.001 for LVs and P=0.004 for SVs) compared to those with less severe TR. Tricuspid annular plane systolic excursion values were the only investigated parameter found to be associated with survival (hazard ratio, 0.814; 95% confidence interval, 0.694 to 0.954; P=0.011). Conclusion: Our results demonstrated a direct association between cardiac congestion (i.e., the severity of TR) and liver stiffness, which should be kept in mind during the assessment of fibrosis in patients with PAH.