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Öğe Adsorption and desorption characteristics of epigallocatechin-3-gallate from discarded green tea leaves on macroporous resin(Springer Int Publ Ag, 2025) Bilcanoglu Cagan, Basak; Karakaya, Huseyin; Yilmaztekin, MuratGreen tea (Camellia sinensis) is intensely consumed all over the world and tea leaves discarded from production are a rich source of catechins, especially epigallocatechin-3-gallate (EGCG). This study aimed to perform preparative separation of EGCG from green tea waste by using macroporous resin and to reveal adsorption and desorption characteristics. Nine types of resins were compared for their adsorption and desorption capacities and desorption rate of EGCG, and NKA-2 was found the most suitable resin for the purpose. Adsorption isotherms were evaluated at 25 degrees C, 35 degrees C and 45 degrees C. Experimental data were well described with pseudo-second-order kinetics model and fitted best to the Langmuir model in tested temperatures. In dynamic separation process, 83% of adsorbed EGCG was recovered from the resin by using 70% ethanol. It has been thought that using macroporous resin can be an effective way of EGCG separation from green tea waste for commercial purposes. [Graphical abstract]Öğe Bioaccessibility of 5-hydroxymethylfurfural in fruit molasses using an in vitro digestion model and risk assessment based on molasses consumption in Turkiye(Taylor & Francis Ltd, 2025) Karakaya, Huseyin; Bilenler Koc, Tugca; Karabulut, IhsanMolasses is a functional food produced by concentrating fruit juice at high temperature and is prone to 5-hydroxymethylfurfural (HMF) formation. In this study, the bioaccessibility and exposure risk of HMF in grape, mulberry, and carob molasses were investigated. According to a validated HPLC analysis, HMF contents of the molasses were determined in the range of 1.95-108.63 mg/kg. The mean HMF concentration was found to be significantly higher (p < 0.05) in grape molasses. Molasses and HMF standard solutions were separately subjected to in vitro digestion to investigate the change in HMF concentration. The HMF content in aqueous solution decreased to 58% in the fluid containing digestive enzymes, while there was no significant change in the medium without enzymes. This suggests that HMF bio-accessibility is greatly influenced by digestive enzymes. After simulated digestion of molasses, it was found that only 70%-79% of the initial HMF concentration was detectable in the digestive mediums. Based on risk assessment data, the chronically daily intake of HMF from molasses was above the threshold of concern. This study emphasises the importance of measuring contaminant concentrations not only in food matrices but also in the gastrointestinal tract when determining actual exposure levels.Öğe 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, KubraCitrus 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.Öğe Kamkat (Fortunella margarita L.) meyvelerinin kimyasal bileşiminin belirlenmesi üzerine kapsamlı bir çalışma(2025) Bilenler, Tugca; Karakaya, Huseyin; Öztürk, Fatma Sezer; Yaşar, KübraKamkat (Fortunella margarita L.) tipik aromaya sahip küçük boyutlu bir meyve grubudur. Bu çalışmada, kamkat meyvesinin β-karoten, sorbitol, şekerler, organik asitler ve fenolikleri içeren kimyasal bileşiminin belirlenmesi amaçlanmıştır. Yüksek Performanslı Sıvı Kromatografisi (HPLC) analizine göre, taze meyvede β-karoten içeriği 0.43 mg 100 g-1 olarak bulunmuştur. Sakkaroz, 3,19 mg 100 g-1 oranı ile şeker içeriğinin yarısından fazlasını oluşturmuştur. Sitrik asit kamkatta en bol bulunan organik asit olmuştur. F. margarita'nın fenolik bileşimini ortaya çıkarmak için toplam 14 fenolik bileşik araştırılmış ve sonuçlar meyvenin büyük bir fenolik çeşitliliğine sahip olduğunu göstermiştir. Gallik asit (277.3 mg 100 g-1), prosiyanidin B1 (119.3 mg 100 g-1) ve epigallokateşin (89.3 mg 100 g-1) bütün meyvede tespit edilen başlıca fenolik bileşiklerdir. Meyve soyulmadan yenildiği için, kabuk uçucu yağı (PEO) da Gaz Kromatografisi-Kütle Spektrometresi'nde (GC-MS) analize tabi tutulmuştur. PEO’nun monoterpenler, seskiterpenler, oksijenli terpenik bileşikler, esterler ve aldehitlerin bir karışımı olduğu belirlenmiştir. Monoterpenik bir madde olan limonen (%83.8) PEO’daki başlıca aromatik bileşen olup, bunu β-mirsen (%6.7), germakren D (%3.3) ve α-pinen (%1.8) takip etmektedir. Bu çalışma, kamkat meyvesinin biyoaktif bileşikler için doğal bir kaynak olduğunu göstermiştir.Öğe Natural Vanillin Production from Isoeugenol by Using Pseudomonas putida in Biphasic Bioconversion Medium(Galenos Publ House, 2022) Karakaya, Huseyin; Yilmaztekin, MuratVanillin, is one of the most demanded flavoring agents in the world. Because of insufficient supply of natural vanillin, market demand is usually supplied by synthetic ones. In this study, it was investigated possibility of usage biphasic system in bioconversion of isoeugenol to vanillin by Pseudomonas putida (HUT 8100). Organic phase was composed of isoeugenol while biocatalyst, P. putida culture, was dispersed in aqueous phosphate solution. Isoeugenol was used as sole carbon source in concentrations ranging between 50-600 g L-1. Incubation was performed at 28 degrees C, at pH 6.3 and 180 rpm shaking. Effect of initial substrate concentration and bioconversion time were investigated. Isoeugenol and vanillin amounts in medium were simultaneously analyzed in HPLC system. After 120 h incubation, vanillin reached the its highest level when 400 g L-1 isoeugenol was applied in medium. In specified conditions, it was achieved to produce 11.95 g L-1 vanillin with 6.2% molar yield within 15 days of bioconversion. It is thought that, obtained result by using biphasic system is very important for the industrial applications in production of natural vanillin via bioconversion.
