Study On The New Technology Of Extraction And Separation Of Alginic Acid And Fucoidan From Seaweed

Our country is rich in seaweed resources,so many seaweed processing industries have been developed,of which the development of alginic acid industry is relatively mature.Alginic acid has the advantages of non-toxicity,anti-oxidation and high biocompatibility,and is widely used in the fields of food,biomedicine,daily chemicals,textile printing and dyeing,and wastewater treatment.At present,the method of digesting brown algae with sodium carbonate is mainly used in industry to extract alginic acid/alginate.This method is relatively mature,but there are drawbacks such as cumbersome processes and product quality that are easily affected by various factors.Therefore,exploring a reagent capable of selectively leaching alginate is of great significance for alginic acid process optimization.For fucoidan,the domestic problem is the difficulties caused by mass production.Exploring an efficient and economical method to isolate fucoidan will be beneficial to its industrial development.In this paper,the method of extracting alginic acid from kelp with DESs3 system and extracting fucoidan from the sporophytes of wakame with lactic acid are proposed.First,this article uses DMI,N-methyloxymorpholine,and DESs3 to extract alginic acid from kelp.The optimal leaching system was selected as DESs3,and the process conditions for leaching polysaccharides in kelp were optimized.The mass fraction of DESs3 was 10%,the mesh number of kelp was 80 mesh,the temperature was 90℃,the leaching time was 2 h,and the solid-liquid ratio was 1:20,the leaching frequency is 1 time,the yield of the obtained polysaccharide is 10%～11%.At the same time,ethanol was used to precipitate the polysaccharides in the leaching solution.The optimal alcohol precipitation conditions were as follows:the volume fraction of ethanol was 75%,the temperature was 30℃,and the alcohol precipitation time was 1.5 h.At this time,the alcohol precipitation rate reached 97.23%.Using the difference in the properties of fucoidan and alginic acid,the alginic acid in the crude polysaccharide product was precipitated by adding acid to adjust the p H value.The results showed that the precipitation rate of the crude polysaccharide solution in hydrochloric acid reached 91.68%.At the same time,the determination of the content of sulfate groups in the crude product of polysaccharide indicates that the main component of polysaccharide is alginic acid.Secondly,lactic acid was used to leaching the wakame spores to obtain fucoidan.After leaching at 90℃for 2 hours,the mass fraction of lactic acid was 4.74%.The yield of crude fucoidan was 7.896%,and the content of alginic acid was 18.03%.Six parallel experiments were carried out.The average yield of crude fucoidan was 7.71%,and the relative standard deviation was 2.81%.The content of alginic acid was stable at 17%to 18%,and the average was 17.33%,relative standard deviation was 2.62%,the data is relatively stable,and the content of sulfate groups in the fucoidan is10.76%.In this study,the kinetics and thermodynamics of alginic acid leaching in the DESs3 system were studied,and the kinetic equation was Y=0.9674e^-0.05856t+0.03177,R²=0.9966,and the leaching processΔH=38.195 k J/mol,ΔS=119.72 J/（mol·K）.ΔH>0 indicates that the process of leaching alginic acid in kelp by this system is an endothermic reaction,and increasing the temperature is beneficial to the leaching of alginic acid in kelp.Finally,the leaching mechanism of alginic acid was discussed by means of FT-IR analysis.The results showed that O on DESs3 attacked H on the carboxylic acid group,forming a new hydrogen-oxygen bond,which became a carboxylate.Meanwhile,the nitrogen on DESs3 and the oxygen on the sugar ring forms a new NO bond to achieve the purpose of extracting alginic acid.The structures of alginic acid and fucoidan were determined,and the two polysaccharides were distinguished by the intensity of the two peaks at 1224 cm^-1 in the spectrum.This paper uses DESs3 system to extract alginic acid,which simplifies the extraction steps and reduces the generation of waste liquid,which is beneficial to promote the development of alginic acid industry,and the use of lactic acid to extract fucoidan from the spore leaves of wakame is a new extraction method.