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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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    Natural Vanillin Production from Isoeugenol by Using Pseudomonas putida in Biphasic Bioconversion Medium
    (Galenos Publ House, 2022) Karakaya, Huseyin; Yilmaztekin, Murat
    Vanillin, 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.