Determination of ash content and concomitant acquisition of cell compositions in microalgae via thermogravimetric (TG) analysis

Thermogravimetric (TG) techniques are widely used in thermal characteristic studies of microalgae combustion and pyrolysis. Ash content is an important parameter for evaluating the cultivation efficiency of photosynthetic microalgae. In this study, microalgal ash content was determined using an optimized protocol that included a heating rate of 20 °C/min from room temperature to 600 °C; a temperature of 600 °C was then maintained for 30 min under an air atmosphere for TG analysis. At temperatures over 600 °C, the ash content was reduced due to the loss of relatively volatile minerals. Four species of microalgae with selectively enriched carbohydrate, protein or lipid contents under different culture conditions were identified via derivative thermogravimetric (DTG) graph analysis, for which characteristic DTG fitting peaks for carbohydrates, protein and lipids were used as reference peaks. Therefore, a qualitative or semi-quantitative analysis of the carbohydrates, proteins and lipids in microalgae based on TG analysis, which concomitantly determines ash content, can be easily performed using only 5-10 mg of sample. The proposed method is rapid and easy, providing composition information for strain screening and physiological studies during microalgae cultivation.