Valorization of regional crude glycerol. Culture media optimization for batch docosahexaenoic acid (DHA) production with Aurantiochytrium sp.

Docosahexaenoic acid (DHA) has many benefits for human health. Commercial DHA sources derive from marine fish but present several production challenges. Aurantiochytrium sp., an abundant marine microalga, becomes an alternative for DHA production. Crude glycerol produced by small-scale biodiesel refineries is a regional, available, and inexpensive waste that can be converted into value-added compounds. This study investigated crude glycerol as a potential carbon source for DHA-rich oil production using an aerobically isolated Aurantiochytrium sp. in batch shake flasks. We also optimized the culture medium formulation by varying carbon and nitrogen sources, thereby reducing medium costs while maximizing DHA production. A larger initial Aurantiochytrium sp. inoculum improved cell concentration and medium carbon depletion, increasing DHA productivity (PDHA). Increasing culture time showed no differences in Aurantiochytrium sp. growth parameters, but reduced DHA production. The absence of yeast extract in the culture media resulted in faster substrate metabolism by Aurantiochytrium sp. and increased DHA production. Crude glycerol yielded the highest PDHA (15.35 mg L-1 h-1) at 120 h. Crude glycerol can be used as a cheaper carbon source in media formulation with Aurantiochytrium sp. cultures for DHA production. Highlights: • Crude glycerol is a cheap and highly available carbon source used by Aurantiochytrium for ω-3 DHA-rich oil production. • Absent yeast extract in culture media enabled faster glucose metabolism, favoring lipid production and improving CTFA and CDHA. • The largest initial inoculum (10.0% v/v) of Aurantiochytrium improved DCW, substrate depletion and PDHA. • BCG medium yielded the highest CDHA and PDHA (84 g L-1 and 15.35 mg L-1 h-1, respectively) at 120 h. • Quality assays of ω-3 DHA-rich oil product showed it is safer for human and animal food formulation.