Date Published: March 30, 2018
Publisher: Springer Berlin Heidelberg
Author(s): Hao Hu, Lin-Lin Ma, Xiao-Fei Shen, Jia-Yun Li, Hou-Feng Wang, Raymond Jianxiong Zeng.
In this study, Tisochrysis lutea was cultivated in mixotrophic and heterotrophic cultures with glycerol as a carbon source and with glucose and acetate for comparison; autotrophic cultivation was the control group without a carbon source. It was found that T. lutea used glycerol and did not use glucose and acetate under mixotrophy. Mixotrophy slightly elevated the docosahexaenoic acid (DHA) and total fatty acids (TFA) content in the dry-weight and enhanced the DHA and TFA production in medium (41.3 and 31.9% respectively) at the end of a 16-day cultivation, while heterotrophy reduced the DHA content and TFA production. Under the mixotrophy, the glycerol contribution to the DHA production (16.19 mg/L) and the TFA production (97.8 mg/L) was not very high and the DHA yield [2.63% chemical oxygen demand (COD)] and TFA yield (13.1% COD) were also very low. Furthermore, T. lutea using glycerol had a period of adaptation, indicating that T. lutea was not an ideal microalga for organic carbon utilization.
Docosahexaenoic acid (DHA) has a high medical and nutritional value; it promotes visual acuity and neural development (Boelen et al. 2013), and reduces the risk of some diseases such as cardiovascular, arthritis, diabetes, and obesity related breast cancer (Biscione et al. 2007; Lee et al. 2012; Manni et al. 2017). As a result, DHA has received worldwide attention in past decades. The primary commercial source of DHA is marine fish oil (Khozin-Goldberg et al. 2011); however, DHA has certain disadvantages, such as unstable quality, a fishy odor, environmental pollution, a long production period, high processing costs, and easy oxidation (Maehre et al. 2015). Microalgae might be the most promising alternative because they are the primary producers of DHA and the DHA in fish oil is derived from microalgae (Ryckebosch et al. 2014). In addition, microalgae-derived DHA overcomes the disadvantages of DHA from marine fish (Martins et al. 2013).