| Summary: | 碩士 === 國立中興大學 === 食品暨應用生物科技學系 === 94 === The previous studies on the determination of heterotrophic cultivation conditions under dark environment in shaken flasks for a useful algal strain, Chlorella sorokiniana NCHU-6, was continued in this study. Medium optimization using experimental designs was performed further in this study in order to increase further the growth yield and cellular chlorophyll content. Moreover, the optimum medium obtained was examined by using the 5-L table-top fermentor without illumination. Finally, some antioxidant activities of the algal powder obtained were also investigated.
The urea used in the previous studies was replaced with the glycine, glutamic acid or sodium glutamate. The results showed both PCV (packed cell volume) (80 ml/L) and chlorophyll content 59 mg/L were significantly increased after 5 days of cultivation when glycine (30 mM) was used.
The influence of glucose, glycine, potassium nitrate and initial pH value were examined initially using a three-level full-factorial design. When the data were analyzed using the first-order model, linearity as a possible model was excluded because the F value of the lack of fit test for PCV and chlorophyll was significant (>5%). Therefore, the second-order model was adopted for approach of gaining more precisely predicted value.
The second-order regression model and the response surface model (RSM) were employed. The stationary point of PCV is a saddle point and the predicted value is 74.18 ml/L, while the stationary point of chlorophyll content is at the maximum point and the predicted value is 58.34 mg/L.
The optimum medium composition for chlorophyll production of C. sorokiniana NCHU-6 was thus determined by RSM as follows (per liter): glucose, 61.87 g; glycine, 2.91 g; KNO3, 14.45 g; initial pH: 6.79; MgSO4.7H2O, 1.5 g; KH2PO4, 1.5 g; FeSO4.7H2O, 0.12 g; EDTA-Na2, 0.12 g; A5 solution, 6 ml. The chlorophyll content up to 67.05 mg/L was obtained using the above optimum medium in a confirmative test, which was higher than those obtained in the previous studies.
The optimum medium composition determined was further examined in a 5-L fermentor. The cultivation was performed at 28℃, aeration rate 1.0 vvm with pH being fixed at 6, 7, 8, or without any control. As a result, the PCV up to 86 ml/L and chlorophyll content 68.61 mg/L were obtained when pH value of broth was not controlled.
The reducing power of cold-water or ethanol extracts of algal powder were 0.81 and 0.47 for 10 mg/ml, respectively. Scavenging DPPH activity of water extract (at 5 mg/ml) was 98.81%, while the value was 95.86% for ethanol extract (5 mg/ml). At 10 mg/ml, chelating effects for Fe2+ were in order of water extract (91.88%) > ethanol extract (86.46%). Finally, TEAC (trolox equivalent antioxidant capacity) values of ethanol extract (10 mg/ml) is 2.55 mg/ml; and water extract (10 mg/ml) is 0.68 mg/ml.
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