Amino acids rich biomass cultivation: Trophic mode influence on Chlorella Growth Factor (CGF) production

Abstract

Nutritional supplement derived from protein-rich microalgae holds significant promise for both livestock and mankind. Chlorella sp. is unique and advantageous due to its ease of cultivation and presence of high composition of proteins, amino acids, and essential micronutrients. A comprehensive three-stage evaluation was conducted to assess different trophic modes (autotrophic, mixotrophic, and photoheterotrophic) and their impact on biomass production and nutritive value. These stages involved trophic mode cultivation (Stage-I) with varied carbon and nitrogen concentrations compared to nutrient deprived condition (control (N1)), CGF production and extraction (Stage-II), and CGF application (Stage-III). In Stage I, mixotrophic modes (M1 and M2) demonstrated the highest biomass production at 4.91 and 4.98 g L-1, surpassing autotrophic (A1 and A2), photoheterotrophic (H1), and nutrient-deprived (N1) conditions. Kinetic modelling revealed a correlative dependence of Chlorella sorokiniana growth on the supplemented nutrients. Scaling up the condition (M1) in a 5 L photobioreactor in Stage-II yielded a biomass of 4.63 g L-1 which was subjected to CGF extraction. In stage-II, C. sorokiniana exhibited a higher quantum efficiency of photosystem II (Fv/Fm: 0.77) and nutritive value, including 412.2 mg g-1 protein and 308 mg g-1 carbohydrate. Extracted CGF constituted of 54.4 % protein having eight essential amino acids (EAA) at 26.36 %, with a total EAA content of 13.7 g/100 g, slightly exceeding commercially available soy meal (12.5 g/100 g). In Stage-III, the applicability of CGF as a substrate for ethanol production using Saccharomyces cerevisiae was assessed, resulting in a biomass of 1.71 g L-1 and ethanol production of 4.5 %. This underscores the potential of C. sorokiniana not only as a rich nutritional source but also for the production of biobased products.