Phd Degree / Doktora

Permanent URI for this collectionhttps://hdl.handle.net/11147/2869

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Author: search.filters.author.Baysal, Ayşe Handan

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  • Doctoral Thesis
    Applications of Mid-Ir Spectroscopy for Identification of Wine and Olive Yeasts and Characterization of Antimicrobial Activities of Phenolics on Yeasts
    (Izmir Institute of Technology, 2015) Canal, Canan; Özen, Fatma Banu; Baysal, Ayşe Handan
    The aim of this study was application of mid-IR spectroscopy in combination with multivariate statistical analysis for characterization of yeasts from two fermented products, wine and olive, in comparison with cultural and molecular tests and characterization of antimicrobial effects induced by olive phenolics on yeasts. Totally 19 wine yeasts were molecularly identified as M. pulcherrima (11%), P. membranifaciens (16%), H. uvarum (5%) and S. cerevisiae (68%). According to FTIR spectroscopic data of wine samples, S. cerevisiae isolates formed a cluster which were generally separated from all other yeasts. Totally 182 olive yeasts were identified from naturally debittered Hurma and a common olive variety and their leaves. The most common yeasts were Metschnikowia sp. (39%) and Aureobasidium sp (78%) in the first and the second harvest years, respectively. Since only Aureobasidium sp. was the common yeast isolated from Hurma during both years, any link between natural debittering of Hurma and the yeast population of this olive type might be related to Aureobasidium sp. Molecularly identified yeast types generally formed different clusters and showed spectral differences. For antimicrobial activity tests, all phenolic compounds were found effective on both S. cerevisiae and A. pullulans; however, A. pullulans was observed to be more sensitive. Antimicrobial activity was differentiated with respect to treatment time and phenol concentration with statistical treatment of FTIR data. As a complementary technique, FTIR could be successfully used for identification of yeasts and characterization of antimicrobial activity of phenolics against yeasts.
  • Doctoral Thesis
    Resistance Properties and Control of Alicyclobacillus Acidoterrestris
    (Izmir Institute of Technology, 2014) Molva, Çelenk; Baysal, Ayşe Handan
    Spoilage caused by Alicyclobacillus acidoterrestris is a significant problem for the fruit juice industry. Since A. acidoterrestris can withstand to high temperatures and acidic environments, it has been suggested as the target organism for the design of thermal processes of fruit juices. On the other hand, little is known about the effect of the sporulation media on the wet–heat resistance characteristics. Moreover, the control of vegetative cell growth and spore germination in fruit juices by natural antimicrobials needs to be studied. Therefore, the objectives of this study were to determine the effects of sporulation media on the thermal inactivation kinetics of A. acidoterrestris DSM 3922 spores in the reconstituted apple juice using different sporulation media; to test the antimicrobial activities of natural plant extracts (grape seed and pomegranate fruit extract), to investigate the growth characteristics in pomegranate juice and pomegranate–apple blend juices (10–80%, v/v); and finally to observe the structural changes using scanning electron and atomic force microscopy. The results of this study clearly showed that spores had different structural, physicochemical and wet–heat resistance properties depending on the sporulation media. Especially, higher wet–heat resistance was obtained from spores produced on mineral containing media. In addition, the high heat resistance of spores was correlated to their higher dipicolinic acid content and Ca2+ ions in the core. Nevertheless, the required dose to inhibit spore germination in the apple juice with natural extracts and in pomegranate and blend juices (40% and 80%) was dependent on the type of antimicrobial, its concentration and sporulation media. Also, the growth of vegetative cells was inhibited in the apple juice with grape seed and pomegranate extracts; and in pomegranate and blend juices (40% and 80%). Then, the experimental inactivation data were fitted satisfactorily using the Weibull model. Microscopic studies suggested that the phenolic compounds in these natural extracts and juices might cause the leakage of cellular components from the cells and prevent the development of the spores into vegetative forms. The results obtained in this study will provide contributions for the design of thermal processes and to prevent the spoilage caused by A. acidoterrestris in the fruit juice industry.
  • Doctoral Thesis
    Antimicrobial, Antioxidant Properties and Chemical Composition of Some Spices/Herbs
    (Izmir Institute of Technology, 2013) Yavuzdurmaz, Hatice; Baysal, Ayşe Handan
    The present study aims to investigate the chemical composition, antimicrobial activity, and mechanism of antimicrobial activity, antioxidant properties of essential oils and extracts and the effects of them when applied to minced beef samples. For this purposes; four essential oils (bay leaf, thyme, clove and cumin), two extracts (grape seed and olive leaf) and constituents of essential oils (eucalyptol, linalool, α-terpineol and α-pinene) were subjected to related tests. Chemical characterization was complemented for all essential oils and extracts. Antimicrobial activity was examined against Staphylococcus aureus, Escherichia coli O157:H7, Salmonella Typhimurium, Listeria innocua, Shewanella putrefaciens, Carnobacterium divergens and Serratia liquefaciens. All tested compounds were effective on the bacteria with different concentrations. Antioxidant activity was proved by FRAP and DPPH methods. Physical disturbance and changes in the structures of bacteria was demonstrated by various techniques. The activity of two most potent essential oils (thyme and clove) was investigated in the minced meat application study. The findings represented that clove essential oil restricted the growth of S. Typhimurium and coliform bacteria. They did not have a significant inhibition effect on the aerobic mesophilic bacteria, total yeasts and molds and also psychrotrophic organisms. The results indicated that L* and a* values were maintained during the storage period. The featured effect of essential oils was antioxidant characteristic in meat application study. All treatment showed significant reduction in oxidation comparing with control. The obtained results may suggest that tested essential oils possess compounds with antimicrobial characteristic as well as antioxidant activity and therefore they can be used as natural preservatives in food especially in meat products.