Studies On Physiology Of Porphyridium Cruentum Affected By Light Quality And Extracting Microalgal Protein

In recent years,the capacity of Porphyridium to enhance biomass by the developing microalgae biotechnology has been significantly improved.Ulitilizing Porphyridium biomass to produce functional food is a hot topic in the field of food research.However,the existing microalgae biotechnologies to develop Porphyridium biomass still meet the following bottlenecks,such as the high cost and low biomass production;which have restricted the sustainable development for Porphyridium biomass in the food application.To address these problems,the aims of this study are to:1)investigate the effect of different light source by light-emitting diodes on the Porphyridium cruentum growth and the abilities for bioactive compounds synthesis;2)illustrate the influence of different nitrogen concentration on the phycobiliproteins,lipid and polysaccharide contents of Porphyridium under the opitimized light source;3)develop a novel multiphase separation technique and optimize its parameters to extract the water-dissolved proteins of Porphyridium cruentum.This work will play a vital role in developing high-valued microalgal bioproducts from Porphyridium cruentum.The main results obtained are shown as follows:The effects of different light source(green,blue,red and white)on the growth of Porphyridium cruentum and synthesis of bioactive compounds were investigated using open-column bubbling photobioreactors.Microalgae cells were cultivated in the cell inoculum size of 0.1 g/L at 3000 Lux,25?,5%CO₂ and 1 L/min air rate.The obtained results were:After 18d of cultivation,the microalga by green light achieved the highest biomass(2.93 g/L),while the lowest microalgal biomass(1.12 g/L)was obtained by the red light.For the blue light,microalga gave the highest content of phycoerythrin(B-PE,59.49 mg/L)on the 15^th day.In term of protein synthesis,the microalgal protein content for four light sources gradually increased and then decreased.Microalgae cells showed the highest protein content in the blue light and the lowest protein content in the red light.With respect to the polysaccharide synthesis,Porphyridium cruentum by gren light exhibited superior ability to synthesize the polysaccharide(intracellular polysaccharide,607.21 mg/L;extracellular polysaccharides,255.62 mg/L)at the end of experiment.For the lipid synthesis,PA,LA,ARA,and EPA were the main fatty acids synthesized by Porphyridium cruentum cells after 18 days of cultivation.In the white light source,the contents for these four main fatty acids were 27.63%,17.31%,24.52%,and 21.51%,respectively.The content of polyunsaturated fatty acids accounted for more than 60%of the total fatty acids.The influences of different potassium nitrate concentration(0,0.5,1 and 1.5 g/L)on the growth of Porphyridium cruentum cell and contents of bioactive substances under the green light were deeply studied,the white light source was selected as the control group,The nitrogen source is potassium nitrate.The experimental results were presented as follows:Compared with the results by white light,microalgal cell preferentially produced higher biomass in the same condition.The highest Porphyridium cruentum biomass(3.09g/L)was attained at the nitrogen concentration of 1 g/L.However,when the nitrogen concentration was in the range of 0.5-1.5 g/L,The protein content of Porphyridium cruentum increased firstly and then decreased.Porphyridium cruentum achieved the highest phycocyanin content(11.68mg/L)in the 0.5g/L nitrogen concentration by white light on the 12^th day.The prolonged cultivate time led to the decrease in phycocyanin content.Microalgal cells in the all nitrogen concentration by green light showed superior ability for intracellular polysaccharide synthesis in comparison to the results by white light.The highest intracellular polysaccharide content(638.73 mg/L)of Porphyridium cruentum was found in the 1.5 g/L nitrogen concentration by green light.After 18 days of cultivation,the total content of unsaturated fatty acids in Porphyridium cruentum cells was associated with the initial nitrogen concentration.The total omega-6 fatty acids content was over 40%of TFAs.In order to extract the water-dissolved protein from from wet Porphyridium cruentum biomass,a multiphase extraction technique(MTET)mediated with(NH₄)₂SO₄,water and tert-butanol was developed and its parameters were optimized to achieve the maxium extraction value for water-dissolved protein.Under the optimized conditions,MTET had 44%extactiion value for water-dissolved protein from microalgae cell.Based on these results,it was indicated that this novel developed MTET with tert-butanol at room temperature was a green and cost-effective method.The MTET process is the potential to produce high-valued microalgal bioproducts by Porphyridium strain for food application.