Optimizing heterotrophic production of Chlorella sorokiniana SU-9 proteins potentially used as a sustainable protein substitute in aquafeed

Alternative protein sources for the reduction/replacement of fish meal in aqua-feeds are in urgent demand. Microalgae are considered sustainable protein sources for aquaculture due to their high-quality proteins with a complete profile of essential amino acids. This study examined the heterotrophic production of proteins from Chlorella sorokiniana SU-9. Culture parameters for maximal biomass and protein production are as follows: glucose - 10 g/L glucose, sodium nitrate - 1.5 g/L, and iron - 46 mu M iron in BG-11 medium. Under optimal conditions, biomass content, protein content and protein productivity of SU-9 reached 4.14 +/- 0.20 g/L, 403 +/- 33 mg/g and 382 +/- 36 mg/L/d, respectively. The protein profile of Chlorella sorokiniana SU-9 is comparable to fishmeal and soybean meal. The essential amino acids arginine, lysine and cysteine, along with glutamine and glutamate, were high. The production cost of SU-9 can be significantly reduced under heterotrophic cultivation conditions, making it a potential protein substitute in aquafeed.