Rhodotorula Cinsine Ait Bazı Maya Türlerinin Beta-Karoten Üretimlerinin İncelenmesi

Abstract

ABSTRACT

INVESTIGATION OF BETA-CAROTENE PRODUCTIONS OF SOME YEAST SPECIES THAT BELONG TO Rhodotorula GENUS

Fazilet MIDIK

Doctor of Philosophy, Department of Food Engineering Supervisor: Prof. Dr. Z. Yeşim ÖZBAŞ August 2021, 252 pages

In this thesis, the effects of various fermentation parameters on β-carotene production by the Rhodotorula glutinis var. glutinis NBRC 1125 strain were studied. All batch fermentations were carried out in water baths with controlled temperature and agitation speed. β-carotene production by each of ten different strains belonging to the genus Rhodotorula was quantitatively assessed. Among the strains examined, the highest β-carotene production (3.68 mg/L) was obtained in the Rhodotorula glutinis var. glutinis NBRC 1125 strain. Thus, β-carotene production by this strain was investigated using different fermentation media containing various carbon and nitrogen sources. In experiments using glucose, fructose, galactose, maltose, or sucrose were used as carbon source, the highest β-carotene production was obtained with galactose (5.57 mg/L) followed by fructose (3.88 mg/L). Further studies were conducted using fructose (the cheaper of these 2 substrates). In experiments in which ammonium sulfate, sodium nitrate, and ammonium chloride were used as inorganic nitrogen sources, and meat, casein, soy-based peptone, and yeast extract were used as organic nitrogen sources, the highest β-carotene yield (6.84 mg/L) was obtained in medium containing a mixture of casein-based peptone and ammonium sulfate. To optimize the β-carotene production of the R. glutinis var. glutinis NBRC 1125 strain, it was subjected to response surface methodology. Using a rotatable central composite design method, an experimental plan consisting of 30 experiments with six replicates at the center point was adopted. Initial fructose and peptone concentrations in the fermentation media, and initial pH and temperature of fermentation medium were selected as independent variables. The dependent variables were β-carotene concentrations, specific growth rates of R. glutinis var. glutinis NBRC 1125, and product formation rate. Multiple regression analysis was applied to the results of all experiments, and equations were derived to model the effects of independent variables on dependent variables. Performance of the derived equations was evaluated using analysis of variance (ANOVA). Optimization was performed numerically using the program’s desirability function. Among the 100 solutions derived from the program, the one having a desirability value of 1.000 was selected for further experiments. In this solution initial fructose and peptone concentrations, initial pH, and temperature of the fermentation medium were 49.459 g/L, 8.371 g/L, 3.815 ve 27.402ºC, respectively. These conditions were selected for further experiments. Experiments performed under these selected conditions yielded a maximum β-carotene concentration was found as 7.18 mg/L, the specific growth rate of R. glutinis var. glutinis NBRC 1125 was 0.025 h-1, and the maximum β-carotene production rate was 0.031 mg β-carotene/(L.h). Statistical analyses of these experiments performed under optimum conditions verified that all experimental results were within acceptable limits, and optimum conditions were confirmed to be within 95% confidence intervals.

This thesis also reported the effects of the direct usage of various natural substrates as fermentation media or usage of natural substrates as carbon source in synthetic fermentation medium on β-carotene production by R. glutinis var. glutinis NBRC 1125. In this study, sugar beet pulp, grape, apple, and pear pulp extracts, chestnut and hazelnut shells, Jerusalem artichoke hydrolysates, and grape juice were used as natural substrates. The highest β-carotene concentration (8.46 mg/L) was obtained using apple pulp extract as carbon source in fermentation medium. In the experiments in which natural substrates were used directly as fermentation media, the highest β-carotene concentration (5.48 mg/L) was obtained with Jerusalem artichoke hydrolysate.

The molecular structures of some β-carotene samples produced by the studied strain were analyzed using FT-IR spectrometer. The spectra of all analyzed samples were consistent with the characteristic peaks of pure β-carotene.

Keywords: Rhodotorula glutinis, β-carotene, fermentation, response surface methodology, optimization, natural substrate