Semi-batch heterotrophic cultivation of Chlorella sorokiniana and Chlorella kessleri: lipid and protein content, fatty acid distribution and FAME properties

Abstract

In the present study the heterotrophic growth of Chlorella sorokiniana and Chlorella kessleri cultivated in a fed-batch mode, using crude glycerol as the sole carbon source, was investigated. The effect of the mode of the organic carbon addition on the lipid and protein content of the biomass, the fatty acid (FAs) distribution of the bio-oil and the fatty acid methyl ester (FAME) properties was studied. The FAME properties namely, the saponification number, the iodine value, the cetane number and the higher heating value, were estimated from empirical equations. The duration all cultivations was 26 d and until the 20th day 800 mL glycerol were added in the cultivation medium (2.3% v/v). For C. sorokiniana, during the cultivation period, 400, 200 and 80 mL glycerol were added in the cultivation medium at 2, 4 and 10 equal intervals respectively. For C. kessleri 400, 200, 100 and 40 mL glycerol were added at 2, 4, 8 and 20 equal intervals, respectively. For C. sorokiniana lipid and protein content ranged from 35.1% to 47.5% and 16.4% to 21.8%, respectively. The percentage of short chain FAs (C10-C14), medium chain FAs (C16-C18) and long chain FAs (>C18) in the total FAs ranged from 6.6% to 19.8%, 80.2% to 91.3% and 0% to 13.1%, respectively. The percentage of saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs) of the total FAs ranged from 25.9% to 37.2%, 38.4% to 60.0% and 14.1% to 24.4%, respectively. For C. kessleri lipid and protein content ranged from 27.7% to 35.1% and 21.5% to 29.8%, respectively. The percentage of short chain FAs, medium chain FAs and long chain FAs of the total FAs ranged from 15.8% to 30.6%, 66.2% to 76.8% and 1.9% to 14.7%, respectively. The percentage of SFAs, MUFAs and PUFAs of the total FAs ranged from 38.7% to 54.1%, 40.7% to 53.1% and 5.2% to 16.3%, respec-tively. Although the treatment 2 × 400 mL of glycerol shows very good FAME properties for both species, the lipid productivities of C. sorokiniana are higher compared to those of C. kessleri and thus, C. sorokiniana is a better option compared to C. kessleri for potential use in biodiesel production. © 2022 Desalination Publications. All rights reserved.