Optimization To Carotenoids Production By Photosynthetic Bacteria And Analysis Of Their Stabilities

The selection of optimum species of photosynthetic bacteria for carotenoid production was carried out, and then culture medium and culture conditions for the growth of the bacteria were optimized with production yield of carotenoids as index. The optimization for extraction of carotenoids from photosynthetic bacteria was performed using response surface methodology. Consequently, the physic-chemical properties of carotenoids extracted from photosynthetic bacteria were investigated in this dissertation. The major working and findings were summarized as follows:1. A strain of photosynthetic bacteria (Rhodobacter sphaeroides) with high production of carotenoids was screened out by the whole-arrangement design, and then main ingredients of culture medium for synthesis of carotenoids by the photosynthetic bacterium was optimized using response surface design, Placket-Burman design and Uniform design. It was indicated that the optimum culture medium for sythesis of carotenoids by the photosynthetic bacterium was Citric acid 8.1g/L,NH₄Cl 3.5 g/L, Corn syrup 1.8 g/L, MgSO₄ 0.12 g/L, Na₂HPO₄ 2.05 g/L, FeSO₄ 0.03 g/L and Na₂CO₃2.22 g/L, the highest production yield of carotenoids reached 17.126 mg/L, being 2.66 times of the preliminary production of carotenoids.2. The volumn of inoculation and pH value of culture medium had significant effect on the carotenoids production (p<0.05). The order of the effect of investigated factors on carotenoids production was arranged as follows: pH value >volumn of inoculation > light intensity. The opitinum conditions for sythesis of carotenoids by photosynthetic bacteria were volumn of inoculation 10 %, pH 7.0 and light intensity 3000 lx. Under those conditions, the production of bacteria and carotenoids reached 4.00 g/L and 23.35 mg/L respectively, which were 11.73% and 42.15% higher than preliminary ones. 3. The process parameters for carotenoids extraction from photosynthetic bacteria were optimized by Box-Behnken design. The optimum conditions for carotenoids extraction were obtained as follows: temperature 30℃, solvent-solid ratio 40 and time 40 min. The carotenoid production yield of extraction was 4790μg /g at first time. The total carotenoids yield extracted from the photosynthetic bacterium twice was 6225μg/g, which was almost accounted for 94.89 % of the total content of carotenoids in the photosynthetic bacterium.4. Based on the analysis of physiochemical properties of the carotenoids from the photosynthetic bacterium, it suggested the carotenoids were unable to be dissoloved in water, but could be dissolved in aceteon and aether. When concentrated H₂SO₄ was added to ethanol solution containing carotenoids, the color of layer below was blue. The effects of temperature, metal ion, acid, alkali, light and oxidant on stability of the carotenoids were investigated. It was indiacted that K⁺, Na⁺, Mg²⁺, Al³⁺, Ca²⁺ and NaOH with low concentration (≤0.01 mol/L) had little effect on stability of the carotenoids, while Fe³⁺, Cu²⁺and NaOH with high concentration (> 0.5 mol/L) would lead to great loss of the carotenoids. The carotenoids were sensitive to light, the order of the effects of the light from different light sources on stability of the carotenoids was: natural light > bulb light > fluorescent light > ultraviolet light. The carotenoids were stable to H₂O₂, only a little decomposition of carotenoids occurred when H₂O₂ existed.