Selection of extraction solvents for edible oils from microalgae and improvement of the oxidative stability.

Microalgae are natural, green raw material and could be used for the development of edible oil for its abundant polyunsaturated fatty acids, with fast growth rate. The wet mud and dry powder of Scenedesmus dimorphus were applied to compare the extraction effects of different organic solvent systems in this study. The results displayed that, by using the ethanol/n-hexane (3:2, v/v) mixed solvent, the oil extraction rate from wet algal mud was 68.31 %, with 71.65 % of neutral lipid, and 1.87 % of vitamin E; the retention rates of protein, chlorophyll, and carbohydrates in the algal residue after oil extraction were 60.56 %, 53.27 %, and 80.20 %, respectively. Through the single solvent n-hexane, the oil extraction rate from dried algal powder was 71.52 %, with 75.86 % of neutral lipids, and 1.63 % of vitamin E. The retention rates of protein, chlorophyll, and carbohydrate were 55.92 %, 61.33 % and 78.35 %, respectively, suggesting the high rate of nutrient retention. In addition, the orthogonal experiments indicated that the compound of low concentration natural antioxidants with 0.010 % of tea polyphenols, 0.005 % of vitamin E, and 0.015 % of rosemary extract had the best effects on improvement of oxidative stability.

Enhancing CO2 utilization by a physical absorption-based technique in microalgae culture.

Carbon dioxide supplementation is significant for cell growth in autotrophic cultures of microalgae. However, the CO2 utilization efficiency is quite low in most processes. Aimed at this problem, six kinds of physical absorption enhancers were investigated to enhance the biological carbon sequestration of microalgae. By the addition of a small amount of CO2 absorption enhancer, the total inorganic carbon concentration of the medium was significantly increased. In addition, the biomass productivity of Scenedesmus dimorphus was maximally increased by 63% by the addition of propylene carbonate in flask cultures. In cultures using an air-lift photobioreactor equipped with a pH-feedback control system to supply CO2, the CO2 consumption was maximally reduced by 71% with added polyethylene glycol dimethyl ether. This study indicates that the incorporation of physical absorption enhancers could be a promising approach to overcome the problems of low CO2 utilization efficiency and high carbon source cost in algal biomass production.