Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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Author: search.filters.author.Harsa, Hayriye ŞebnemSubject: search.filters.subject.Fermentation

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Now showing 1 - 4 of 4
  • Master Thesis
    L[+]-Lactic Acid Purification From Fermentation Broth Using Ion Exchange Resins
    (Izmir Institute of Technology, 2002) Polat, Zelal; Harsa, Hayriye Şebnem
    Lactic acid exists in two optically active form, D(-) and L(+)-lactic acid. It has been used in food, leather, textile, pharmaceutical and cosmetic industries. Moreover, L(+)-lactic acid constitutes the raw material for the production of poly-L-lactic acid which is used in biomedical applications.The aim of this study was to recover and purify the microbially produced L(+)-lactic acid from the fermentation media efficiently and economically. Among the various downstream operations, ion exchange chromatography was used since it is highly selective and yields a low cost product recovery within a short period of time. The additional goals were to investigate the end product purity, to obtain new data on the adsorption/desorption behaviours of lactic acid and to investigate the applicability of the system for industrial usage. In this project, Lactobacillus casei NRRL B-441 was used for the production of L(+)-lactic acid from whey by a 12 hours fermentation process at pH 5.5 and 37 oC. The product concentration was 50 g/l with 100% L(+)-lactic acid content. Then, a suitable resin with high sorption capacity and rapid equilibrium behavior was selected. The selected resin was Dowex marathon WBA, a weakly basic anion exchanger in OH form. It reached the equilibrium state in 15 minutes. The batch sorption experiments were done at pH 7.0 and 30 oC and sampling was continued for 20 hours. Furthermore, the effect of temperature and pH was investigated and their influence was found to be unimportant. All the adsorption/desorption experiments were applied both to model lactic acid and to biomass free fermentation broth. The ion exchange equilibria of lactic acid and L(+)-lactic acid in fermentation broth on Dowex marathon WBA were explained by the Langmuir isotherm. The maximum exchange capacity (qm) for model lactic acid was 0.25 g La/g wet resin, while L(+)-lactic acid in fermentation broth has a qm value of 0.04 g La/g wet resin. The equilibrium loading and exchange efficiency of L(+)-lactic acid in fermentation broth were reduced as a result of competition by other ionic species. The competing ions inhibit the binding of L(+)-lactic acid to the free sites of ion exchanger. Moreover, column operations were applied to recover sorbed lactic acid from the ion exchanger. 2.0 M HCl was found to be a suitable eluting agent to recover the bound L(+)-lactic acid with a flowrate of 1 ml/min at ambient temperature. About 95 % of bound L(+)-lactic acid was recovered from Dowex marathon WBA.
  • Master Thesis
    Effects of Trace Elements on the Production of Baker's Yeast
    (Izmir Institute of Technology, 2002) Üzelyalçın, Berna; Harsa, Hayriye Şebnem
    Baker.s yeast has been used widely in traditional bakeries to produce different kinds of baked products and for many biotechnological purposes. The principal raw materials used in producing baker.s yeast are the pure yeast culture and molasses. Cane molasses and beet molasses contain 45 to 55 % sugar in the forms of sucrose, glucose, and fructose. Molasses, which is a rich carbon and mineral source, contains most of the nutrients and minerals required for baker.s yeast production. Nutrients and trace elements (magnesium, copper and zinc) that are not present in sufficient quantities in molasesses are added to the fermentation medium. In this study, the effects of Ca2+, Mg2+, Cu2+ and Zn2+ on baker.s yeast production were investigated. The method of Food Composition Laboratory (FCL), Human Nutrition Research Center, Beltsville, US, was used for the preparation of the fermentation samples prior to ICP-AES analysis. The concentrations of Ca2+, Mg2+, Cu2+, Zn2+ were determined in the raw materials entering the fermentors and the products. FCL digestion method was evaluated on precision and accuracy; linear standard curves were obtained for the studied concentration ranges of Ca2+, Mg2+, Cu2+ and Zn2+. Standard addition curves for each element in 45 brix molasses and dry yeast samples were constructed and spike recovery percentages were calculated. High spike recovery percentages were obtained for all elements in both dry yeast and molasses with the FCL method. In industrial fermentations, uptakes of Ca2+, Cu2+, Mg2+ and Zn2+ by the yeast cells were calculated as mg/kg dry yeast at 4h time intervals. The uptake rates were evaluated based on the available element concentration in the medium and the uptake of the elements. Results showed that, as the uptake of Ca2+ increased with time, uptake of Mg2+, Cu2+ and Zn2+ decreased. The yeast cells used the available elements with decreasing uptake rates except Ca2+. During the first hours of fermentation, uptake rates were high. The maximum uptake rates observed for each element in two different industrial fermentations were: 17.73-23.32 mg Cu2+/ kg dry yeast cells , 195.64-413.46 mg Zn2+ / kg dry yeast cells, 2106.46-2051.74 mg Mg2+ / kg dry yeast cells. Ion concentrations of biomass in industrial fermentations revealed that same amounts of Mg were taken by the cell from the fermentation medium under similar conditions. This was verified by the studies done in lab-scale using pure culture of S.cerevisiae, grown on different concentrations of Mg2+. It was found that uptake of Mg2+ was constant and very close to the uptake values of industrial fermentations. 806.7 mM Mg2+ was taken by 1 kg of dry yeast cells. This is in agreement with the stated Mg2+ uptake concentration range 500-1000 mM of Saccharomyces cerevisiae in literature. In the industry, magnesium is added in the form of Mg.SO4.7H2O to the fermentation medium. SO42- ions coming from the MgSO4.7H2O cause settling problems in the waste treatment system of the plant. Generally, molasses contain sufficient concentration of Mg2+ ions required for baker.s yeast production in the industrial scale. Since Mg2+ has toxic effects at high concentrations and its addition is increasing the cost of the process and causing difficulties in the waste treatment of the plant, it may be concluded that addition of Mg2+ as MgSO4.7H2O to the fermentation medium should be done after determining the Mg2+ concentration of molasses. Instead of using excessive amounts of MgSO4.7H2O, only the required quantity should be added to the fermentation medium.
  • Master Thesis
    Determination of Whey-Based Medium Requirements and Growth Characteristics for the Production of Yoghurt Starter Cultures
    (Izmir Institute of Technology, 2008) Soydemir, Elçin; Harsa, Hayriye Şebnem
    Yoghurt is an important dairy product which is produced by thermophilic starter cultures including; Streptococcus thermophilus and Lactobacillus bulgaricus. They grow synergistically in milk by acidifying milk, produce specific aroma compounds and lactic acid which impact the quality of the yoghurt. Imported cultures are widely used in dairy industry to stabilize the technological properties which cause a change in our natural flora and flavour. Starters from traditional yoghurts have to be preserved. Under this perspective, the aim of this study was to determine the medium requirements of mixed starter cultures for production of starter bacteria which has been isolated and characterized before.Determination of medium requirements were done in a whey-based media. Since bacteriophages were one of the most important problem in dairy industry, to prevent cultures from phage adsorption, media was treated with different salts which can bind free calcium ions. Salts were examined for cell viability and phage infection effects.From these studies Na2HPO4 + KH2 PO4 with 2% of medium addition was chosen as the most effective. Mineral requirements of the mixed cultures were determined. The best combination; 10, 5, 50 ppm for Fe2+, Mn2+, Mg2+ ions with 0,939 desirability were used for initial mineral content of medium. Fermentation constants for mixed cultures were determined. Pure culture fermentations and mixed culture fermentations were performed. According to results mixed culture inoculations gave higher maximum specific growth rates; 0,9188h-1 and 0,7323h-1 for cocci and bacilli while 0,855h-1 and 0,659h-1 were obtained for cocci and bacilli from single strain fermentations.
  • Master Thesis
    Lactic Acid Production by Lactobacillus Casei Nrrl B-441 Immobilized in Chitosan Stabilized Ca-Alginate Beads
    (Izmir Institute of Technology, 2005) Gündüz, Meltem; Harsa, Hayriye Şebnem
    Having two optically active forms, D(-) and L(+) lactic acid has long been used in the food, chemical, textile, pharmaceutical and other industries. 90 % of the worldwide production of lactic acid is by bacterial fermentation. Recently, there is an increasing interest in the production of L(+) lactic acid, since it is a potential substrate for polylactic acid that is biocompatible and can be used for medical purposes. Whey, which is a by-product of dairy industry, contains approximately 5 % (w/v) lactose. Since whey has a high BOD content, it possesses serious environmental problems. Whey lactose is a good substrate for lactic acid bacteria and can be used for L(+) lactic acid fermentations. This study focuses on the production of lactic acid from whey by Lactobacillus casei NRRL B-441 immobilized in chitosan stabilized Ca-alginate beads. Higher lactic acid production and lower cell leakage were observed with alginate-chitosan beads compared with Ca-alginate beads. The highest lactic acid (131.2 g/l) was obtained with cells entrapped in 1.3-1.7 mm alginate-chitosan beads prepared from 2 % Na-alginate. acid production and lower cell leakage were observed with alginate-chitosan beads compared with Ca-alginate beads. The highest lactic acid (131.2 g/l) was obtained with cells entrapped in 1.3-1.7 mm alginate-chitosan beads prepared from 2 % Na-alginate. The gel beads produced lactic acid for 10 consecutive batch fermentations without marked activity loss and deformation. Response surface methodology was used to investigate the effects of three fermentation parameters (initial sugar, yeast extract and calcium carbonate concentrations) on the concentration of lactic acid. No previous work has used statistical analysis in determining the interactions among these variables in lactic acid production by immobilized cells. Results of the statistical analysis showed that the fit of the model was good in all cases. Initial sugar, yeast extract and calcium carbonate concentrations had strong linear effects on lactic acid production. Maximum lactic acid concentration of 136.3 g/l was obtained at the optimum levels of process variables (initial sugar concentration.147.35 g/l, yeast extract concentration. 28.81 g/l, CaCO3 concentration.97.55 g/l). These values were obtained by fitting of the experimental data to the model equation. The response surface methodology was found to be useful in optimizing and determining the interactions among process variables in lactic acid production using alginate-chitosan immobilized cells.