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    Biological control of green mould on mandarin fruit through the combined use of antagonistic yeasts
    (Academic Press Inc Elsevier Science, 2023) Oztekin, Sebahat; Karbancioglu-Guler, Funda
    Penicillium digitatum is the primary cause of green mould in mandarins during the postharvest period, mainly controlled through synthetic fungicides. This study evaluated the biocontrol of green mould on mandarin fruit with three antagonistic yeasts (Hanseniaspora uvarum, Meyerozyma guilliermondii, and Metschnikowia aff. pul-cherrima P01A016), alone or in combination, by elucidating their possible mechanisms of action. All yeast cultures alone (73.85 % -80.64 %) and their combinations (78.40 % -83.18 %) reduced the mycelial growth of green mold in vitro. M. aff. pulcherrima reduced the disease incidence and lesion diameters by 75.5 % and 91.3 %, respectively, demonstrating the highest biocontrolling activity alone. Meyerozyma guilliermondii showed the highest biofilm formation (OD 0.93 +/- 0.01) and antifungal activity (71.13 %) through volatile organic com-pounds (VOCs), while H. uvarum displayed cell-wall degrading beta-1,3 glucanase activity together with mycoci-nogenic and VOCs activity. All tested yeasts showed chitinase, protease, and leucine arylamidase activity. Among dual combinations, M. guilliermondii and M. aff. pulcherrima (M-1) were the most compatible, while M. aff. pulcherrima and H. uvarum (M-3) had the least compatibility. The combined application of these three yeasts resulted in synergistic co-operation, demonstrating the highest biocontrolling efficacy in vitro and in vivo. Inte-grating multiple mechanisms of action in yeasts could create a hurdle approach for inhibiting green mould in citrus as a green alternative to synthetic fungicides. Thus, our study demonstrated that combining biocontrol yeasts can result in beneficial consortia for the eco-friendly and sustainable management of P.digitatum-caused postharvest diseases of mandarins in both the wounded and intact mandarin fruits.
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    Bioprospection of Metschnikowia sp. isolates as biocontrol agents against postharvest fungal decays on lemons with their potential modes of action
    (Elsevier, 2021) Oztekin, Sebahat; Karbancioglu-Guler, Funda
    In this study, various fruit were employed as biocontrol yeast reservoirs, and eleven distinct yeast cultures of Metschnikowia sp. belonging to 6 different species were identified with sequence-based analysis of the D1/D2 domain of 26S rDNA. For initial screening, Metschnikowia isolates were tested on Fusarium oxysporum, Botrytis cinerea, Penicillium digitatum, Penicillium expansum, and Alternaria alternata. The highest antagonism was obtained on green and blue Penicillium (83.63-100 %). All tested yeasts showed chitinase activity, while some had protease, pectinase, cellulase, beta-1-3 glucanase, and gelatinase activities. Since lemons have high pectin content, three pectinase-free cultures at tested conditions with high in vitro antagonism on Penicillium were selected and used on lemons. The activities of the in vitro antifungal studies were found to be compatible with those of the in vivo, and P. digitatum's incidence was found to be higher than that of P. expansum on lemons. All tested pectinasefree Metschnikowia sp. lead to a significant reduction in the disease incidences and lesions at varying levels. The combined effect of lytic enzyme secretion, iron depletion, and volatile organic compounds (VOCs) production determined the antifungal mechanism of action. M. aff. fructicola demonstrated the highest biocontrol efficacy against Penicillium on lemons with an increasing shelf-life. The use of tentatively pectinase-negative Metschnikowia sp. as an antifungal biocontrol agent on lemons was considered for the first time. The findings will shed light on the effective use of Metschnikowia sp. as a potential biofungicide against the growth of postharvest fungal pathogens.
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    A novel exopolysaccharide from cold-adapted yeast Rhodotorula glutinis, along with structural, rheological, antioxidant, and antibiofilm properties
    (Springer Heidelberg, 2023) Oztekin, Sebahat; Dikmetas, Dilara Nur; Karbancioglu-Guler, Funda
    In the present study, a novel exopolysaccharide EPS-BMD26 produced by cold-adapted yeast Rhodotorula glutinis was structurally examined, along with its rheological, antioxidant, and antibiofilm properties. High-performance liquid chromatography (HPLC) analysis revealed glucose and galactose as two monosaccharide constituents. The functional groups within the EPS-BMD26 structure were detected by Fourier transform infrared (FT-IR) spectroscopy. The H-1 and C-13 nuclear magnetic resonance (NMR) spectra of EPS-BMD26 also confirmed its beta-D-glucan type with galactose residues with an average molecular weight of 118 kDa. Differential scanning calorimetry (DSC) analysis revealed that EPS-BMD26 had a high level of thermal stability, up to 326.16 degrees C. Scanning electron microscopy (SEM) analysis demonstrated that EPS-BMD26 had a porous microstructure with fissures. X-ray diffraction (XRD) analysis revealed its semi-crystalline nature. EPS-BMD26 showed moderate and concentration-dependent antioxidant potential recruiting different methods, including center dot OH, DPPH center dot, CUPRAC, and ABTS radical scavenging activities. Water-soluble EPS-BMD26 exhibited high water holding capacity of 190 +/- 0.22% with a water solubility index of 60.6 +/- 8.3%. At 1.25 mg mL(-1), EPS-BMD26 inhibited biofilm formation of Staphylococcus aureus ATCC 25923 by 79.5%. Rheological characterization revealed that the aqueous solution of EPS-BMD26 had shear thinning and pseudoplastic behavior. Given these properties, EPS-BMD26 may be a promising bio-hydrocolloid, antibiofilm agent, and food additive for industrial applications.
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    Recent Insights into the Use of Antagonistic Yeasts for Sustainable Biomanagement of Postharvest Pathogenic and Mycotoxigenic Fungi in Fruits with Their Prevention Strategies against Mycotoxins
    (Amer Chemical Soc, 2023) Oztekin, Sebahat; Dikmetas, Dilara Nur; Devecioglu, Dilara; Acar, Emine Gizem; Karbancioglu-Guler, Funda
    Fungi-induced postharvest diseases are the leading causesof foodloss and waste. In this context, fruit decay can be directly attributedto phytopathogenic and/or mycotoxin-producing fungi. The U.N. SustainableDevelopment Goals aim to end hunger by 2030 by improving food security,sustainable agriculture, and food production systems. Antagonisticyeasts are one of the methods presented to achieve these goals. Unlikephysical and chemical methods, harnessing antagonistic yeasts as abiological method controls the decay caused by fungi and adsorbs and/ordegrades mycotoxins sustainably. Therefore, antagonistic yeasts andtheir antifungal mechanisms have gained importance. Additionally,mycotoxins' biodetoxification is carried out due to the occurrenceof mycotoxin-producing fungal species in fruits. Combinations withprocesses and agents have been investigated to increase antagonisticyeasts' efficiency. Therefore, this review provides a comprehensivesummary of studies on preventing phytopathogenic and mycotoxigenicfungi and their mycotoxins in fruits, as well as biocontrolling andbiodetoxification mechanisms.
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    Recruiting grape-isolated antagonistic yeasts for the sustainable bio-management of Botrytis cinerea on grapes
    (Wiley, 2024) Oztekin, Sebahat; Karbancioglu-Guler, Funda
    Botrytis cinerea is the causative agent of grey mould disease in grapes, which was linked to significant postharvest losses. This study examined three grape-isolated yeasts (Metschnikowia aff. fructicola, Metschnikowia pulcherrima, and Hansenispora uvarum) through in vitro and in vivo tests on detached grape berries against grey mould, as well as the elucidation of their possible mechanisms of action. The antifungal mechanism of action of yeasts was determined by the lytic enzyme activity, inhibition of spore germination, biofilm activity, iron depletion, diffusible metabolites, wound-site colonisation, mycocin, and volatile organic compounds (VOCs) production. The highest in vitro efficacy (83.13%) was observed on M. aff. fructicola, followed by M. pulcherrima (82.10%) and H. uvarum (71.66%). Metschnikowia yeasts exhibited comparable enzyme activities, including protease, beta-1,3 glucanase, gelatinase chitinase, and cellulase, while H. uvarum had a poor enzymatic activity with chitinase and gelatinase. M. aff. fructicola showed relatively higher iron depletion activity than M. pulcherrima, while M. pulcherrima outperformed via diffusible metabolites. All yeast cultures significantly reduced spore germination by at least 86%. Overall, M. aff. fructicola exhibited the highest biocontrol activity with its iron depletion, inhibition of conidial germination, biofilm formation, VOCs, and well colonisation on grape berries. M. aff. fructicola 1-UDM outperformed all other yeasts by significantly reducing disease incidence and lesion diameter values (93.4% and 94.3%, respectively). Remarkably, H. uvarum VOCs demonstrated potential as a biofumigant for suppressing grey mould. All yeasts are well adapted to their ecological niche to bio-protect grapes from grey mould disease.
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    Simultaneous Detection of Ochratoxin A and Aflatoxins in Industrial and Traditional Red and isot Pepper Flakes along with Dietary Exposure Risk Assessment
    (Amer Chemical Soc, 2022) Oztekin, Sebahat; Karbancioglu-Guler, Funda
    This study focused on the co-occurrence of aflatoxins (AFs) and ochratoxin A (OTA) in traditionally and industrially dried red pepper flakes (DRPFs) and isot pepper flakes (IPFs). Following the multitoxin immunoaffinity column (IAC) clean-up, high-performance liquid chromatography coupled with fluorescence detection (HPLC-FLD) was used to quantify AFs and OTA. The limit of detection (LOD) and limit of quantification (LOQ) values were 0.11 and 0.18 mu g kg(-1) (AFB1), 0.04 and 0.08 mu g kg(-1) (AFB(2)), 0.13 and 0.18 mu g kg(-1) (AFG(1)), 0.04 and 0.11 mu g kg(-1) (AFG(2)), and 0.10 and 0.21 mu g kg(-1) (OTA), respectively. AFB(1), AFB(2), AFG(1), and OTA were found to be positive in 93, 74, 17, and 94% of all samples, respectively. The contamination levels in positive samples ranged from 0.23 to 38.69, 0.04 to 2.14, 0.13 to 0.88, and 0.18 to 52.19 mu g kg(-1) for AFB(1), AFB(2), AFG(1), and OTA, respectively, while no AFG(2) was found above the detection limit (0.04 mu g kg(-1)). None of the industrial isot peppers exceeded the European Union limits, while the levels of AFB(1) (5 mu g kg(-1)), total AFs (10 mu g kg(-1)), and OTA (20 mu g kg(-1)) of the traditional peppers were above the limit by 30% (16/54), 26% (14/54), and 4% (2/54), respectively. Co-occurrence of AFB(1)-AFB(2)-OTA was the most frequent, accounting for 54% (29/54) of all samples. At the upper bound (UB), estimated average exposure to AFB(1), total AFs, and OTA was determined to be 0.175, 0.189, and 0.124 ng kg(-1) bw day(-1) in all samples, respectively. The margin of exposure (MoE) value of AFB(1) and total AFs was found to be 977 and 909, indicating high health concerns compared to OTA (MoE >10,000). AFB(1) and total AFs may result in 0.0058 and 0.0062 liver cancer cases/100,000 person/year at UB, respectively, and weekly OTA exposure was 0.868 ng kg(-1) bw, well below the provisional tolerable weekly intake, hence not of health concern. AFs exposure could endanger health, whereas OTA posed no toxicological concerns through dried red pepper consumption