Optimizing protein production from an indigenous microalga Chlorella vulgaris FSP-E

Abstract

Fishmeal is the most widely used protein source in commercial aquacultural feed However due to its unstable production and increasing price using fishmeal is getting more uneconomical in aquaculture Therefore finding its alternatives is in urgent demand Among the potential fishmeal alternatives microalgae have been recognized as the most promising one In this study a protein-rich indigenous microalgal isolate identified as Chlorella vulgaris FSP-E was selected for protein production to assess its potential to serve as fishmeal alternative In the beginning an innovative photobioreactor combined with cold cathode fluorescent lamps (CCFLs) as internal illumination was designed to improve microalgal protein production The internal illumination could enhance biomass productivity to 411 mg/L/d and protein productivity to 183 mg/L/d due to its higher light intensity and reduction of self-shading effect When the initial urea concentration in the medium was increased to 12 4 mM the biomass productivity and protein productivity were further improved to 613 mg/L/d and 301 mg/L/d respectively For medium improvement the culture was conducted under different iron concentrations The result shows the biomass productivity and protein productivity were enhanced to 699 mg/L/d and 365 mg/L/d respectively when using an iron concentration of 90 μM In addition the amino acid analysis of the microalgal protein shows that over 60% of protein in the microalga was necessity amino acids Therefore the nutritional value of the microalgal protein was enhanced by iron concentration supplement in the growth medium Moreover the working capacity of microalgae culture was scaled up to 50 liter while several strategies were applied to enhance the feasibility of mass culture of microalga C vulgaris FSP-E The results show that the immersed light source installed inside the tubular photobioreactor resulted in an obvious improvement on overall biomass productivity (up to 170 mg/L/d) while the maximal protein content could reach 59 6% of dry cell weight Next the effect of inoculum size was also investigated on the algae-based protein production The results show that using an inoculum size of 0 1 g/L of C vulgaris FSP-E resulted in higher biomass and protein productivity of 190 mg/l/d and 121 mg/l/d respectively Considering the carbon supply and the mixing efficiency of tubular photobioreactor different CO2 aeration rate was then adjusted to further enhance the performance of algae-based protein production The results show that the biomass and protein productivity were further increased to 213 and 133 mg/L/d respectively with an optimal aeration rate of 0 05 vvm To assess the commercial viability the microalgal cultivation was shifted from indoor to outdoor condition The results show that a similar growth performance was achieved under outdoor condition when compared to the previous indoor results Considering the difference between indoor and outdoor conditions several environmental factors were re-investigated The biomass productivity and protein productivity were improved to 241 mg/L/d and 136 1 mg/L/d after increasing urea concentration to 18 6 mM The growth performance could be further enhanced by increasing inoculum size to 0 2 g/L and the results indicated that the biomass productivity and protein productivity could attain 258 mg/L/d and 149 9 mg/L/d respectively After determining the suitable inoculum size CO2 aeration rate was then adjusted to investigate its effect on the performance of algae-based protein production However the results showed that higher aeration rate repressed algal growth leading to poor protein productivity The high shear stress resulted from high aeration led to a plummet of microalgae protein production performance This study demonstrated that C vulgaris FSP-E is a promising candidate of alternative for fishmeal in aquaculture

Date of Award	2014 Aug 18
Original language	English
Supervisor	Jo-Shu Chang (Supervisor)