Effects of C/N ratio on the growth and protein accumulation of heterotrophic Chlorella in broken rice hydrolysate

Abstract

Background Microalgae protein is considered as a sustainable alternative to animal protein in the future. Using waste for microalgal culture can upgrade low-value raw materials into high-value products, helping to offset the cost of microalgal protein production. In this study we explored the feasibility of using microalgae heterotrophic fermentation to convert broken rice hydrolysate (BRH) into protein. Results The results showed that the increase of BRH supplemental ratio was beneficial to the increase of biomass production but not beneficial to the increase of intracellular protein content. To further improve protein production, the effect of C/N ratio on intracellular protein accumulation was studied. It was found that low C/N ratio was beneficial to the synthesis of glutamate in microalgae cells, which in turn promoted the anabolism of other amino acids and further the protein. When the C/N ratio was 12:1, the biomass productivity and protein content could reach a higher level, which were 0.90 g/L/day and 61.56%, respectively. The obtained Chlorella vulgaris biomass was rich in essential amino acids (41.80%), the essential amino acid index was as high as 89.07, and the lysine content could reach up to 4.05 g/100 g. Conclusions This study provides a theoretical basis and guidance for using Chlorella vulgaris as an industrial fermentation platform to convert broken rice into products with high nutritional value.

Variability in Macro- and Micronutrients of 15 Rarely Researched Microalgae

“…match with those in the literature, yet the overall content does not [ 20 ]. A culture medium with a carbon to nitrogen ratio tending towards nitrogen promotes the production of amino acids [ 21 ]. We assume that a nitrogen-poorer cultivation is causing the lower amino acid concentrations in the analyzed microalgae compared to the literature.…”

“…Microalgae in the growth phase were shown to accumulate more amino acids with two or more nitrogen atoms, such as histidine and arginine but also ornithine. This might be due to a greater availability of nitrogen in the culture medium, since microalgae cultivated in a nitrogen-rich medium synthesize amino acids rich in nitrogen [ 21 ]. Furthermore, the additional increase in the non-protein amino acid ornithine is plausible, due to its role as a precursor for arginine synthesis [ 21 ].…”

“…This might be due to a greater availability of nitrogen in the culture medium, since microalgae cultivated in a nitrogen-rich medium synthesize amino acids rich in nitrogen [ 21 ]. Furthermore, the additional increase in the non-protein amino acid ornithine is plausible, due to its role as a precursor for arginine synthesis [ 21 ]. In recent years, alternatives to animal-based protein sources have been investigated due to the higher demands for food of a continuously increasing human population [ 22 ].…”

Comparison of Different Pretreatment Processes Envisaging the Potential Use of Food Waste as Microalgae Substrate

“…Therefore, these results were somehow expected since FW 5 and 6 have fish in their composition. Regarding the impact of C:N ratios, Cai et al [27] demonstrated the effect of different ratios on the growth and protein accumulation of C. vulgaris grown under heterotrophic culture conditions using rice hydrolysate. This study showed that nitrogen became a limiting factor for microalgal growth when the C:N ratios exceeded 19:1, resulting in lower biomass productivity.…”

“…In general, all the FW formulations had higher ratios than the Redfield ratio, but the value associated with this one (37.22) may have resulted in a more unbalanced supplementation, leading to growth inhibition. For example, the study conducted by Cai et al [27] focused on the influence of different C:N ratios, ranging from 5:1 to 48:1, on the heterotrophic growth of C. vulgaris. It was observed that, at higher ratios, besides inhibiting growth, not all the reducing sugars present in the culture medium were consumed.…”