Aureobasidium Pullulans İle Pullulan Üretimine Etki Eden Çeşitli Parametrelerin İncelenmesi

Abstract

In this thesis, the effects of various fermentation parameters on the pullulan production of Aureobasidium pullulans AZ-6 strain were investigated. Fermentation experiments in the study were carried out in the batch system, in shaking water baths whose temperature and shaking speed could be controlled. In order to determine the strain to be used in the study, pullulan production of seven A. pullulans strains were compared and local A. pullulans AZ-6 strain which produced pullulan at higher concentration (17.56 g/L) was selected for the experiments. When the effects of different carbon sources used in fermentation medium on pullulan production of A. pullulans AZ-6 strain were examined, it was found that sucrose yielded higher pullulan production (15.66 g/L) among glucose, fructose, sucrose, galactose and maltose. In the experiments conducted for determining the nitrogen source that best supports the pullulan production of A. pullulans AZ-6 strain, in the fermentation medium, when as organic nitrogen sources; urea, yeast extract and pepton, as inorganic nitrogen sources; (NH4)2SO4, NaNO3, and NH4Cl were used, maximum pullulan concentration (18.61 g/L) was obtained in the medium in which pepton and (NH4)2SO4 were used together. Later in this study, the optimization of pullulan production with A. pullulans AZ-6 was performed using the response surface methodology. In this scope, an experimental design plan consisting of 30 experimental points with six replicates in the center was created by using the central composite rotatable design method in the software. In this design, while the initial sucrose and peptone concentrations of the fermentation medium, the initial pH and temperature of the fermentation medium were selected as independent variables; the maximum exopolysaccharide (EPS) and pullulan concentrations, the specific growth rate of A. pullulans AZ-6, the maximum specific pullulan formation rate and pullulan yield were selected as dependent variables. After the experiments carried out according to the conditions in the design, model equations showing the effects of independent variables on dependent variables were derived by applying multiple regression analysis on obtained results with the help of the software, and the consistency of these equations were evaluated by variance (ANOVA) analysis. Optimization was performed with the desirability function in the software numerically. The conditions where the value of desirability function was 0.977, the initial sucrose and peptone concentrations and the pH of the fermentation medium were 100 g/L, 11.305 g/L and 6.481, respectively and the temperature was 24.2°C were determined as optimum among the 100 solutions computed by the software. In the experiments carried out under these conditions, maximum EPS and pullulan concentrations, specific growth rate, maximum specific pullulan formation rate and pullulan yield were obtained as; 36.95 and 35.47 g/L, 0.064 h-1 , 0.036 [g pullulan/(g mo.h)], and 54.48%, respectively and optimum conditions were confirmed at 95% confidence level. In the thesis research, the effects of using various preprocessed natural substrate sources directly as a fermentation medium or as the main component of fermentation medium on the pullulan production of A. pullulans AZ-6 strain were also investigated. In the experiments where whey, molasses, grape pulp, sugar beet pulp, melon, watermelon, onion and carrot peels and sweet potato were used as natural substrate sources; maximum pullulan production was obtained when sweet potato extract (37.62 g/L) and molasses solution (18.67 g/L) was used as fermentation medium directly. In this thesis, the effects of UV mutation application on the pullulan production of A. pullulans AZ-6 were also investigated. In these experiments, it was found that the maximum pullulan concentrations (30.84-35.66 g/L) produced by 13 possible mutant strains were very close to each other and the maximum pullulan concentrations produced by these strains were very similar to those of A. pullulans AZ-6’s production under the same conditions. In the thesis research, in molecular structure analyzes performed by FT-IR spectrometer, it was determined that spectra of EPS produced by A. pullulans AZ-6 strain contained characteristic peaks for pullulan. When the molecular weights of some EPS samples obtained in the study were calculated, it was found that; these values vary in the range of 0.49x107 -3.30x107 .