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    Changes in oxidative stability and phytochemical contents of microencapsulated wheat germ oil during accelerated storage
    (Elsevier, 2021) Aslan, Kubra Sengul; Karabulut, Ihsan; Koc, Tugca Bilenler
    Wheat germ oil (WGO) contains high amounts of tocopherols, phytostemls, and carotenoids. The high amount of unsaturated fatty acid content of WGO increases sensitivity to oxidative degradation. This study aimed to assess the efficacy of WGO micmencapsulation in buttermilk (BM) to prevent oxidative degradation. A mixture consisting of WGO:BM (1:2) and water (60%) was emulsified by a high-pressure homogenizer, and then freeze-dried. Both bulk and micmencapsulated WGO samples were kept at 60 degrees C for 24 days to evaluate oxidative stability, changes in contents of tocopherol, phytosterol, and carotenoid. Peroxide and p-anisidine values of micro-encapsulated WGO were significantly lower than the bulk WGO throughout the storage days (p < 0.05). Similarly, tocophemls, phytosterols, and carotenoid contents degraded less in microencapsulated WGO than those in bulk WGO (p < 0.05). Improved stability of the sensitive compounds in WGO through microencapsulation can extend the potential use of WGO's as a functional ingredient in food formulations.
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    Chemical Composition and Antimicrobial Activity of Pummelo (Citrus maxima) Essential Oil Derived from Fruit Peel
    (Taylor & Francis Ltd, 2022) Karakaya, Huseyin; Ozturk, Fatma Sezer; Koc, Tugca Bilenler; Yasar, Kubra
    Citrus genus is notable for peel essential oils which are valuable by-products during Citrus processing. In this study, it was aimed to determine chemical composition and antimicrobial activity of the essential oil of pummelo peel (PEO). The essential oil was obtained by hydrodistillation from flavedo layer of the peel. It was subjected to Gas Chromatography/Mass Spectrometry (GC/MS) for identification of its volatiles and a total of sixty-two compounds were identified. Monoterpenes constituted 89.36% of PEO, mostly by D-limonene (76.97%) and beta-myrcene (6.37%). The essential oil became prominent especially with its nootkatone content (1.13%). In antimicrobial activity assays, broth macrodilution method was used against to Staphylococcus aureus, Bacillus cereus, Escherichia coli, Salmonella Enteritidis, Saccharomyces cerevisiae and Candida albicans. According to the test results, minimum inhibitory concentrations of the essential oil ranged between 2000 and 16000 mu g/mL for S. aureus, B. cereus, S. cerevisiae and C. albicans. No inhibitory effect was observed on E. coli and S. Enteritidis although 32000 mu g/mL PEO was applied. On the basis of the results obtained, it was thought that PEO could be used as a natural and inexpensive flavouring and antimicrobial agent by the food and pharmaceutical industries via valorization of pummelo peel.
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    Determination of Antioxidant Properties and beta-Carotene in Orange Fruits and Vegetables by an Oxidation Voltammetric Assay
    (Taylor & Francis Inc, 2022) Koc, Tugca Bilenler; Savan, Ebru Kuyumcu; Karabulut, Ihsan
    Recently, the evaluation of antioxidant properties using voltammetric techniques based on electrooxidation has attracted considerable attention. In this study, the antioxidant capacity, total phenolic compounds, and beta-carotene content of orange-fleshed fruits and vegetables, including carrots, persimmons, and pumpkins, were evaluated by standard and electrochemical methods. The antioxidant capacity, evaluated by the ABTS and DPPH measurements, and the total phenolic compounds were determined spectrophotometrically. The results were expressed as Trolox equivalent antioxidant capacity (TEAC) and gallic acid, respectively. The beta-carotene contents of the samples were determined by high-performance liquid chromatography (HPLC). Electrochemical measurements were performed with differential pulse voltammetry at a sensor formed by attaching single-walled carbon nanotubes onto the glassy carbon electrode surface. Trolox, gallic acid, and beta-carotene were determined electrochemically with high sensitivity, repeatability, and low detection limits. Regression analysis was performed to correlate the results of the spectrophotometric assays and HPLC with those obtained electrochemically and satisfactory results were obtained.
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    Electrochemical Determination of the Antioxidant Capacity, Total Phenolics, and Ascorbic Acid in Fruit and Vegetables by Differential Pulse Voltammetry (DPV) with a p-Toluene Sulfonic Acid Modified Glassy Carbon Electrode (TSA/GCE)
    (Taylor & Francis Inc, 2023) Koc, Tugca Bilenler; Savan, Ebru Kuyumcu; Karabulut, Ihsan
    The determination of antioxidant capacity, total phenolics, and ascorbic acid using accurate, efficient, low cost, and rapid methods has great analytical importance. The antioxidant capacity, total phenolics, and ascorbic acid content of apricots, arugula, banana, cranberries, spinach, and strawberries were investigated with an electrochemical approach and examined for compatibility with conventional methods. The antioxidant activity was determined by ABTS and DPPH assays. The total phenolic content was determined by the Folin Ciocalteu method and ascorbic acid was quantified by high-performance liquid chromatography (HPLC). In order to perform sensitive and simultaneous electrochemical measurements, the surface of a glassy carbon electrode (GCE) was modified by electropolymerization with p-toluene sulfonic acid (TSA). The TSA/GCE modified sensor was used for the first time for the determination of antioxidant capacity and total phenolic content. The surface of the modified sensor was characterized by cyclic voltammetry and scanning electron microscopy. The TSA/GCE was linearly correlated with the differential pulse voltammetry (DPV) for Trolox and gallic acid in 0.1M NaNO3 and ascorbic acid in pH 7.4 phosphate buffer. Electrochemical methods offer a promising alternative for the determination of antioxidant capacity and total phenolic content due to their simplicity, rapid response, low cost, sensitivity, and reproducibility.
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    Improving the Antimicrobial and Antioxidant Activity of Clove (Syzigium aromaticum L.) Essential Oil by Microencapsulation
    (Taylor & Francis Ltd, 2022) Koc, Tugca Bilenler; Colakdalci, Seyma
    This study aimed to investigate the effect of microencapsulation on the bioactive properties of clove essential oil (CEO). The CEO was microencapsulated into various wall materials, including maltodextrin (MD) and sodium caseinate (SC), and their combination with gum arabic (GA) and gelatin (G), through freeze-drying. The effects of wall material blend (MD-SC, MD-SC-GA, and MD-SC-G) on microencapsulation efficiency, morphology, in vitro release profile, antioxidant and antimicrobial properties were investigated. The MD-SC blend offered the best microencapsulation properties in terms of encapsulation efficiency (86.22%), ideal microcapsule shape, and maximum release rate (85.98%). Microencapsulation extended the radical scavenging time of the CEO. DPPH and ABTS scavenging activities of MD-SC microencapsulated CEO were 83.61% and 82.96% inhibition, while values were 76.37% and 80.03% inhibition for free CEO, respectively. Antimicrobial activities of microencapsulated and free CEO were investigated against eight microorganisms with in vitro (broth microdilution technique) and in-situ tests. Both free and CEO-loaded microcapsules were able to inhibit the growth of Gram-positive bacteria, except for Bacillus cereus, at the same concentration. Microencapsulated CEO exhibited weaker antimicrobial activity on Gram-negative bacteria than free CEO. The influence of the pH of fruit juices and components of milk on the antimicrobial activity of microencapsulated CEO was also evaluated. Microencapsulated CEO may have different antimicrobial effects depending on the pH and content of the food. This study showed that microencapsulation of CEO increased the application dose for antimicrobial effect in foods.
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    Oxidative Stability and In Vitro Release Properties of Encapsulated Wheat Germ Oil in Saccharomyces cerevisiae Cell-Based Microcapsules
    (Wiley, 2021) Cetinkaya, Nilgun; Koc, Tugca Bilenler; Karabulut, Ihsan
    This research aims to evaluate the feasibility of Saccharomyces cerevisiae cell-based microencapsulation for wheat germ oil (WGO) based on oxidative stability and in vitro release properties. Microencapsulation of samples is achieved by freeze-drying WGO-in water emulsions containing alive, non-plasmolyzed, and plasmolyzed yeast cells. The encapsulation efficiency (EE), loading capacity (LC), release characteristics, and oxidative stability of WGO are determined before and after microencapsulation. The amount of beta-carotene in the digesta is used to evaluate the release properties. Plasmolyzed yeast cells yield the highest EE (43.1%) and LC (216.5 g kg(-1)). In cases where alive and non-plasmolyzed yeast cells were used as an encapsulant, a higher release rate was obtained in esophagus-stomach conditions, while higher digestion took place mainly in the duodenum and ileum with plasmolyzed cells. Encapsulation of WGO in plasmolyzed yeast cells provide the lowest peroxide and p-anisidine values and the highest oxidative protection during the accelerated oxidation test at 60 degrees C for 24 days. This result is also confirmed by Rancimat induction time. Practical Applications: Removing the plasma content by plasmolysis changes the structure of the yeast cell membrane and improves the encapsulation ability and release properties. Encapsulation of WGO with plasmolyzed yeast cells provides superiority in oxidative stability compared to native WGO. The potential value of WGO as an ingredient in the preparation of functional foods could be achieved by yeast cell encapsulation.