| Due to their unique nutritional value,Eicosapentaenoic Acid(EPA)and fucoxanthin have a large market demand.The current commercial production cann’t meet the market demand,so it is necessary to find new sources.Pavlova sp.and Phaeodactylum tricornutum contain both EPA and fucoxanthin,which are high in content and easy to extract,and are potential sources for large-scale production of EPA and fucoxanthin.Therefore,this thesis focuses on these two algae to study how to improve their nutritional quality.Below are key research findings:1.The effect of culture time on the growth and substance accumulation of Pavlova sp.and P.tricornutum.Microalgae with different culture time,substance composition and nutritional value are different,so this thesis studied the growth and substance accumulation of Pavlova sp.and P.tricornutum at different culture time.The EPA production of Pavlova sp.varied with little differentce at different culture times,ranging from 14.17-18.54mg/L.The EPA yield of P.tricornutum was the highest on the 9th day(5.62mg/L).In terms of lipid nutritional quality,the shorter culture time,the lower Atherogenic index(AI)and Thrombogenic index(TI),the higher the hypoglycemic olemic index(HI)and hypoglycemic olemic index to hyperglycemic olemic index(h/H),the better the quality of lipid nutrition,were observed.2.Effects of light quality on the growth and substance accumulation of Pavlova sp.and P.tricornutum.Light quality effects the growth and cell composition of microalgae.In this thesis,the effects of light quality on the growth and cell composition of microalgae were studied by using different proportions of combined red and blue light in culture of Pavlova sp.and P.tricornutum.White light was used as the control.The results showed that the combination of red and blue light,especially 2R5B,3R4B,4R3B and 5R2B,had obvious promoting effect on the growth of Pavlova sp.,but had no promoting effect on the growth of P.tricornutum.The lipid production of Pavlova sp.in 4R3B culture was the highest(107.86mg/L),which was 25.61%higher than that of the control.The lipid production of P.tricornutum in 5R2B culture was the highest(75.56mg/L).The combination of red and blue light had no significant effect on the EPA content and production of Pavlova sp.,while 0R7B,1R6B and 7R0B had significant effect on the EPA production of P.tricornutum.Besides,the EPA productions in all combinations of red and blue light except 3R4B were higher than that of the control,especially in the three treatments of 0R7B,1R6B and 7R0B,which were more than 50.00%higher than the control.Different light quality had no significant effect on the lipid nutritional quality of Pavlova sp.,0R7B,7R0B and 1R6B had significant effect on the lipid nutritional quality of P.tricornutum.3.Effects of photoperiod and vitamin on Pavlova sp.and P.tricornutum.The growth of photoautotrophic microalgae is greatly affected by the time of illumination.Vitamin,as an organic growth factor,also has a certain effect on the growth of microalgae and the production of substances.In this thesis,the effects of different photoperiod and vitamin concentrations on Pavlova sp.and P.tricornutum were studied.The results showed that the EPA content and production of 8:16 photoperiod were both the highest,but the content,production and nutrient quality of lipid were the best at 16:8 photoperiod.As for the effects of photoperiod and vitamin on Pavlova sp.,the preliminary experiment found that there were significant differences in dry weight of Pavlova sp.with different photoperiod and vitamin concentrations,and then three photoperiod and three vitamin concentrations were selected for two-factor experiment.It was found that photoperiod,vitamin concentration and their interaction had significant effects on dry weight,photoperiods of 16:8 and 24:0 were conducive to the growth of Pavlova sp.Under the three vitamin concentrations,photoperiods of 24:0 achieved the highest lipid content.The photoperiod had significant effects on fatty acid composition and lipid nutritional quality.The shorter the illumination time,the higher the EPA content and production,the better the lipid nutritional quality were observed.The vitamin concentration had no significant effect on these indexes.4.Influence of culture conditions on fucoxanthin.The accumulation of fucoxanthin in microalgae is affected by various culture conditions.The effects of light,vitamin,silicon content and plant hormones on fucoxanthin were studied in this thesis.The production of fucoxanthine by Pavlova sp.cultured with white light was the highest(1.61mg/L),and that of P.tricornutum cultured with red light was the highest(2.51mg/L).And the productions of fucoxanthine by P.tricornutum cultured with the combined red and blue light were increased by the increase of the proportion of red light.The shorter the light duration was,the higher the fucoxanthin accumulation was observed.At 16:8 photoperiod,fucoxanthin production increased with increasing vitamin concentration.When the Si concentration was 4 times that of the normal f/2 medium,the fucoxanthin production of P.tricornutum was the highest(2.06mg/L),which was 26.76%higher than that of the f/2 medium.Plant hormones also had a certain effect on fucoxanthine production.Fucoxanthine production with ABA was increased by 9.01%compared with control.5.The effect of light quality on photosynthetic activity of Pavlova sp.The chlorophyll fluorescence technique is is an effective tool to study the mechanism of environmental changes affecting photosynthesis of microalgae.In this thesis,the photosynthetic activity of Phavlova sp.under different light quality was studied by chlorophyll fluorescence technique.It was found that the combination of red and blue light increased Fv/Fm and Fv/Fo,and improved the utilization rate of light energy by Pavlova sp.Under red light,the specific activity parameters of ABS/RC,TRo/RC,ETo/RC and DIo/RC were all higher than those of the control.Under 6R1B light,ABS/CSm,TRo/CSm and ETo/CSm were significantly higher than those of the control.In the treatment of 3R4B,α,rETRmax and Ik were the respective largest ones,which helping chlorophylla to absorb,transfer and convert light energy.The three performance indices of PIABS,PICS and PITOTAL under blue light(0R7B)and the combined red and blue light were significantly higher than those under white light(W),which improved the overall PSII performance of Pavlova sp.Photosynthetic activity was also correlated with the growth,substance compositions and lipid nutritional quality of microalgae.TRo/CSm,ETo/CSm are positively correlated with dry weight.PIABS,PICS,and PITOTAL were positively correlated with lipid content and production,that is,their higher values were beneficial to lipid accumulation. |
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