Investigations in ultrasonic enhancement of β-carotene production by isolated microalgal strain Tetradesmus obliquus SGM19

Microalgae constitute relatively novel source of lipids for biodiesel production. The economy of this process can be enhanced by the recovery of beta-carotenes present in the microalgal cells. The present study has addressed matter of enhancement of lipids and beta-carotene production by microalgal species of Tetradesmus obliquus SGM19 with the application of sonication. As first step, the growth cycle of Tetradesmus obliquus SGM19 was optimized using statistical experimental design. Optimum parameters influencing microalgal growth were: Sodium nitrate = 1.5 g/L, ethylene diamine tetraacetic acid = 0.001 g/L, temperature = 28.5 degrees C, pH = 7.5, light intensity = 5120 lux, beta-carotene yield = 0.67 mg/g DCW. Application of 33 kHz and 1.4 bar ultrasound at 10% duty cycle was revealed to enhance the lipid and beta-carotene yields by 34.5% and 31.5%, respectively. Kinetic analysis of substrate and product profiles in control and test experiments revealed both lipid and beta-carotene to be growth-associated products. The intracellular NAD(H) content during late log phase was monitored in control and test experiments as a measure of relative kinetics of intracellular metabolism. Consistently higher NAD(H) concentrations were observed for test experiments; indicating faster metabolism. Finally, the viability of ultrasound-exposed microalgal cells (assessed with flow cytometry) was > 80%.