Microalgae-based biorefinery--from biofuels to natural products.

Microalgae represent a potential source of renewable nutrition and there is growing interest in algae-based dietary supplements in the form of whole biomass, e.g., Chlorella and Arthrospira, or purified extracts containing omega-3 fatty acids and carotenoids. The commercial production of bioactive compounds from microalgae is currently challenged by the biorefinery process. This review focuses on the biochemical composition of microalgae, the complexities of mass cultivation, as well as potential therapeutic applications. The advantages of open and closed growth systems are discussed, including common problems encountered with large-scale growth systems. Several methods are used for the purification and isolation of bioactive compounds, and many products from microalgae have shown potential as antioxidants and treatments for hypertension, among other health conditions. However, there are many unknown algal metabolites and potential impurities that could cause harm, so more research is needed to characterize strains of interest, improve overall operation, and generate safe, functional products.

Microalgae for High-Value Products Towards Human Health and Nutrition.

Lignocellulose: A Sustainable Material to Produce Value-Added Products With a Zero Waste approach-A Review

Heterotrophic cultivation of microalgae for pigment production: A review

Due to the rapid global expansion of the aquaculture industry, access to key feedstuffs (fishmeal and fish oil) is becoming increasingly limited because of the finite resources available for wild fish harvesting. This has resulted in other sources of feedstuffs being investigated, namely plant origin substitutes for fishmeal and fish oil for aquafeed. Conventional land-based crops have been favored for some applications as substitutes for a portion of the fishmeal, but they can result in changes in the nutritional quality of the fish produced. Microalgae can be regarded as a promising alternative that can replace fishmeal and fish oil and ensure sustainability standards in aquaculture. They have a potential for use in aquaculture as they are sources of protein, lipid, vitamins, minerals, pigments, etc. This comprehensive review summarizes the most important and recent developments of microalgae use as supplement or feed additive to replace fishmeal and fish oil for use in aquaculture. It also reflects the microalgal nutritional quality and digestibility of microalgae-based aquafeed. Simultaneously, safety and regulatory aspects of microalgae feed applications, major challenges on the use microalgae in aquafeed in commercial production, and future research and development perspective are also presented in a critical manner. This review will serve as a useful guide to present current status of knowledge and highlight key areas for future development of a microalgae-based aquafeed industry and overall development of a sustainable aquaculture industry.

Microalgae in aquafeeds for a sustainable aquaculture industry

The effect of aeration on the performance of docosahexaenoic acid (DHA) production by Schizochytrium sp. was investigated in a 1,500-L bioreactor using fed-batch fermentation. Six parameters, including specific growth rate, specific glucose consumption rate, specific lipid accumulation rate, cell yield coefficient, lipid yield coefficient, and DHA yield coefficient, were used to understand the relationship between aeration and the fermentation characteristics. Based on the information obtained from the parameters, a stepwise aeration control strategy was proposed. The aeration rate was controlled at 0.4 volume of air per volume of liquid per minute (vvm) for the first 24 h, then shifted to 0.6 vvm until 96 h, and then switched back to 0.4 vvm until the end of the fermentation. High cell density (71 g/L), high lipid content (35.75 g/L), and high DHA percentage (48.95%) were achieved by using this strategy, and DHA productivity reached 119 mg/L h, which was 11.21% over the best results obtained by constant aeration rate.

Development of a stepwise aeration control strategy for efficient docosahexaenoic acid production by Schizochytrium sp.

Aims: To improve the yield and productivity of docosahexaenoic acid (DHA) by Schizochytrium sp. in terms of the analysis of microbial physiology.



Methods and Results:  A two-stage oxygen supply control strategy, aimed at achieving high concentration and high productivity of DHA, was proposed. At the first 40 h, KLa was controlled at 150·1 h−1 to obtain high μ for cell growth, subsequently KLa was controlled at 88·5 h−1 to maintain high qp for high DHA accumulation. Finally, the maximum lipid, DHA content and DHA productivity reached 46·6, 17·7 g l−1 and 111 mg l−1 h−1, which were 43·83%, 63·88% and 32·14% over the best results controlled by constant KLa.



Conclusions:  This paper described a two-stage oxygen supply control strategy based on the kinetic analysis for efficient DHA fermentation by Schizochytrium sp.



Significance and Impact of the study:  This study showed the advantage of two-stage control strategy in terms of microbial physiology. As KLa is a scaling-up parameter, the idea developed in this paper could be scaled-up to industrial process and applied to other industrial biotechnological processes to achieve both high product concentration and high productivity.

Enhancement of docosahexaenoic acid production by Schizochytrium sp. using a two-stage oxygen supply control strategy based on oxygen transfer coefficient.

Different fermentation processes, including batch, fed-batch and repeated fed-batch processes by Schizochytrium sp., were studied and compared for the effective DHA-rich microbial lipids production. The comparison between different fermentation processes showed that fed-batch process was a more efficient cultivation strategy than the batch process. Among the four different feeding strategies, the glucose concentration feed-back feeding strategy had achieved the highest fermentation results of final cell dry weight, total lipids content, DHA content and DHA productivity of 72.37, 48.86, 18.38 g l−1 and 138.8 mg l−1 h−1, respectively. The repeated fed-batch process had the advantages of reducing the time and cost for seed culture and inoculation between each fermentation cycles. The results of fermentation characteristics and lipid characterization of the repeated fed-batch process indicated that this repeated fed-batch process had promising industrialization prospect for the production of DHA-rich microbial lipids.

Batch, fed-batch and repeated fed-batch fermentation processes of the marine thraustochytrid Schizochytrium sp. for producing docosahexaenoic acid

Industrial processes of lignocellulosic material have made use of only the hexose component of the cellulose fraction. Pentoses and some minor hexoses present in the hemicellulose fraction, which may represent as much as 40% of lignocellulosic biomass, have in most cases been wasted. The lack of good methods for utilization of hemicellulose sugars is a key obstacle hindering the development of lignocellulose-based ethanol and other biofuels. In this chapter, we focus on the utilization of hemicellulose sugars, the structure of hemicellulose and its hydrolysis, and the biochemistry and process technology involved in their conversion to valuable fuels and chemicals.

Fuels and Chemicals from Hemicellulose Sugars

Docosahexaenoic acid (DHA) percentage in total fatty acids (TFAs) is an important index in DHA microbial production. In this study, the change of DHA percentage in response to fermentation stages and the strategies to increase DHA percentage were investigated. Two kinds of conventional nitrogen sources, monosodium glutamate (MSG) and ammonium sulfate (AS), were tested to regulate DHA synthesis. Results showed that MSG addition could accelerate the substrate consumption rate but inhibit lipid accumulation, while AS addition could increase DHA percentage in TFAs effectively but extend fermentation period slightly. Finally, the AS addition strategy was successfully applied in 7,000-L fermentor and DHA percentage in TFAs and DHA yield reached 46.06 % and 18.48 g/L, which was 19.54 and 17.41 % higher than that of no-addition strategy. This would provide guidance for the large-scale production of the other similar polyunsaturated fatty acid, and give insight into the nitrogen metabolism in oil-producing microorganisms.

Liang Qu

Papers

Development of a stepwise aeration control strategy for efficient docosahexaenoic acid production by Schizochytrium sp.

Enhancement of docosahexaenoic acid production by Schizochytrium sp. using a two-stage oxygen supply control strategy based on oxygen transfer coefficient.

Batch, fed-batch and repeated fed-batch fermentation processes of the marine thraustochytrid Schizochytrium sp. for producing docosahexaenoic acid

Fuels and Chemicals from Hemicellulose Sugars

Regulation of docosahexaenoic acid production by Schizochytrium sp.: effect of nitrogen addition