A novel two-stage heterotrophic cultivation for starch-to-protein switch to efficiently enhance protein content of Chlorella sp. MBFJNU-17

Application research and progress of microalgae as a novel protein resource in the future

Economic growth and health awareness spotlight opportunities and challenges in the food industry, particularly with decreasing arable land, climate change, dwindling freshwater resources, and pollution affecting traditional protein sources. Microalgae have emerged as a promising alternative, with higher protein content, better nutritional quality, and greater environmental resilience compared to conventional crops. They offer a protein balance comparable to meat, making them a sustainable protein source with health benefits like antioxidants, cardiovascular support, and anti-inflammatory properties. Improving the protein content of microalgae through optimized cultivation techniques is crucial to fully realize its potential as a novel food source. While there are already microalgae-based food products in the market, challenges remain in utilizing microalgal protein for widespread food production, emphasizing the need for further research. This review article explores the impact of microalgae culture conditions on protein content, the physicochemical and nutritional characteristics of microalgal protein, the health advantages of microalgal proteins and their derivatives, as well as research on separating and purifying microalgal proteins and their derivatives. It also delves into the current opportunities and obstacles of microalgal proteins and their derivatives as food, highlighting the potential for investigating the link between microalgal protein food and human health.

Investigating cultivation strategies for enhancing protein content in Auxenochlorella pyrenoidosa FACHB-5

This study investigated the influence of yeast extract addition, carbon source, and photoperiod on the growth dynamics of Auxenochlorella pyrenoidosa FACHB-5. Employing response surface methodology, the culture strategy was optimized, resulting in the following optimal conditions: yeast extract addition at 0.75 g L-1, glucose concentration of 0.83 g L-1, and a photoperiod set at Light: Dark = 18 h: 6 h. Under these conditions, the biomass reached 1.76 g L-1 with a protein content of 750.00 g L-1, containing 40 % of essential amino acids, representing a 1.52-fold increase. Proteomic analysis revealed that the targeted cultivation strategy up-regulated genes involved in microalgal protein synthesis. The combined effect of yeast extract and glucose enhanced both the glutamine synthetase-glutamate synthetase mechanism and the free amino acid content.

Microalgae as fishmeal alternatives in aquaculture: current status, existing problems, and possible solutions

Fishmeal is an indispensable ingredient for most aquatic animals. However, the finite supply and escalating price of fishmeal seriously limit its use in aquaculture. Thus the development of new, sustainable protein ingredients has been a research focus. Microalgae are potential fishmeal alternatives owing to their high protein content and balanced amino acid profile. Studies suggest that suitable replacement of fishmeal with microalgae is beneficial for fish growth performance, but excessive replacement would induce poor growth and feed utilization. Therefore, this paper aims to review research on the maximum substitutional level of fishmeal by microalgae and propose the main issues and possible solutions for fishmeal replacement by microalgae. The maximum replacement level is affected by microalgal species, fish feeding habits, quality of fishmeal and microalgal meals, and supplemental levels of fishmeal in the control group. Microalgae could generally replace 100%, 95%, 95%, 64.1%, 25.6%, and 18.6% fishmeal protein in diets of carp, shrimp, catfish, tilapia, marine fish, and salmon and trout, respectively. The main issues with fishmeal replacement using microalgae include low production and high production cost, poor digestibility, and anti-nutritional factors. Possible solutions to these problems are recommended in this paper. Overall, microalgae are promising fishmeal alternatives in aquaculture.

A semi-continuous efficient strategy for removing phosphorus and nitrogen from eel aquaculture wastewater using the self-flocculating microalga Desmodesmus sp. PW1

The phosphorus content in eel aquaculture wastewater exceeds the discharge standard, and the amount of wastewater discharged is substantial. Therefore, there is an urgent need to explore an economical and efficient method of treating aquaculture wastewater. This study explored the use of Desmodesmus sp. PW1, a type of microalgae, to treat eel aquaculture wastewater. By optimizing the conditions, Desmodesmus sp. PW1 achieved a total phosphorus (TP) removal efficiency of 92.3%, as well as total nitrogen (TN) and ammonia nitrogen (NH4+-N) removal efficiency of 99%, using a photoperiod of 24:0, a temperature of 25 °C, and an inoculation amount of 15%. Furthermore, Desmodesmus sp. PW1 demonstrated a high self-flocculating efficiency (>90%) within 100 min of settling, which facilitated biomass recovery. Subsequently, a semi-continuous treatment process mode was established with a sewage renewal rate of 90%. The results showed that after four rounds of sewage renewal operations, the microalgae biomass in the sewage treatment system could be maintained between 160.0 and 220.0 mg/L, and the average removal rate of TP was 0.13 mg/(L * h). The lipid content of algae cells collected in the semi-continuous treatment system for eel aquaculture wastewater was as high as 36.5%, and the biodiesel properties met the biodiesel standards authorized by Europe and the United States. Overall, this study provides an economical and effective strategy for converting wastewater into high-value microalgae products.

The utility of algae as sources of high value nutritional ingredients, particularly for alternative/complementary proteins to improve human health

As the global population continues to grow, the demand for dietary protein is rapidly increasing, necessitating the exploration of sustainable and nutritious protein sources. Algae has emerged as a promising food source due to their high value ingredients such as proteins, as well as for their environmental sustainability and abundance. However, knowledge gaps surrounding dietary recommendations and food applications restrict algae's utilization as a viable protein source. This review aims to address these gaps by assessing the suitability of both microalgae and macroalgae as alternative/complementary protein sources and exploring their potential applications in food products. The first section examines the potential suitability of algae as a major food source by analyzing the composition and bioavailability of key components in algal biomass, including proteins, lipids, dietary fiber, and micronutrients. Secondly, the biological effects of algae, particularly their impact on metabolic health are investigated with an emphasis on available clinical evidence. While evidence reveals protective effects of algae on glucose and lipid homeostasis as well as anti-inflammatory properties, further research is required to understand the longer-term impact of consuming algal protein, protein isolates, and concentrates on metabolic health, including protein metabolism. The review then explores the potential of algal proteins in food applications, including ways to overcome their sensory limitations, such as their dark pigmentation, taste, and odor, in order to improve consumer acceptance. To maximize algae's potential as a valuable protein source in the food sector, future research should prioritize the production of more acceptable algal biomass and explore new advances in food sciences and technology for improved consumer acceptance. Overall, this paper supports the potential utility of algae as a sustainable and healthy ingredient source for widespread use in future food production.

Optimization of Heterotrophic Culture Conditions for the Algae Graesiella emersonii WBG-1 to Produce Proteins

The aim of this study was to improve the protein content and yield of heterotrophic microalgal cultivation and establish a simple, economical, and efficient method for microalgal protein production using the novel green alga, Graesiella emersonii WBG-1, which has not been previously reported for heterotrophic cultivation. Through batch heterotrophic cultivation of this alga, we observed that glucose was the optimal carbon source, while it could not use sucrose as a carbon source. Biomass production and protein content were significantly reduced when sodium acetate was used as the carbon source. Compared with nitrate, protein content increased by 93% when urea was used as the nitrogen source. Cultivation temperature had a significant impact on biomass production and protein content. The optimal conditions were glucose as the carbon source at an initial concentration of 10 g/L, urea as the nitrogen source at an initial concentration of 1.62 g/L, and a culture temperature of 35 °C. On the second day of batch cultivation, the highest protein content (66.14%) was achieved, which was significantly higher than that reported in heterotrophic cultures of Chlorella and much higher than that reported for specially established technologies aimed at increasing the protein content, such as two-stage heterotrophic, heterotrophy-dilution-photoinduction, and mixotrophic processes. These results demonstrate the great potential of the heterotrophic cultivation of G. emersonii WBG-1 for protein production.

Pilot-scale remediation of rare earth elements ammonium wastewater by Chlamydomonas sp. YC in summer under outdoor conditions

This work evaluated the performance of real rare earth elements (REEs) wastewater purification and carbon dioxide (CO₂) fixation by Chlamydomonas sp. YC with pilot-scale airlift-photobioreactors (AL-PBRs), tubular photobioreactors (TB-PBRs) and raceway ponds (ORWPs) under high-temperature outdoor conditions in summer. The obtained results showed that Chlamydomonas sp. YC at 1 g/L oyster shell piece (OSP) and 3 % CO₂ had the highest biomass (1.9 g/L) and NH₄⁺-N removal efficiency (34.0 %) during the REEs wastewater treatment. Among the selected photobioreactors, Chlamydomonas sp. YC to treat real REEs wastewater at 3 % CO₂ under high-temperature outdoor conditions attained the highest biomass (2.3 g/L) in the TB-PBRs with the best NH₄⁺-N removal efficiency (43.0 %). Furthermore, the input cost and CO₂ net sequestration evaluation revealed that TB-PBRs was more economical photobioreactors to treat REEs wastewater and fix CO₂ by Chlamydomonas sp. YC, providing some vital scientific details for REEs wastewater and CO₂ fixation by microalgal biotechnology.