Biotransformation Of Glycyrrhizic Acid And Flavonoids And Analysis Of Stevia Components

Licorice and stevia are important sources of natural sweeteners.They are hotspots in the research of natural products.Glycyrrhizic acid and stevioside can be not only used as high-potency functional sweeteners,but also both of them are important ingredients of medicinal and edible additives.In this paper,the bioconversion,separation and purification of glycyrrhizic acid were studied,transforming glycyrrhizic acid into glycyrrhetinic acid,which has important medicinal values,such as antivirus,anti-tumor,anti-inflammatory and immunoregulation.Meanwhile,the structures of vitexin and breviscapine were modified by glucanotransferase to increase their solubility and bioavailability.This work also analysised the content of stevioside and stevia phenolic acid from different cultivars of Stevia rebaudiana to provide reference for the quality selection of stevia.(1)In this paper,the microorganism Aspergillus niger was screened to transform monoammonium glycyrrhizinate to glycyrrhetinic acid specifically,and the transformation products were identified by HPLC and LC-MS.Researches were focused on the factors which influenced the transformation efficiency of Aspergillus niger:culture time,transformation temperature,pH and enzyme concentration.Through the transformation conditions:solid culture,culture 5d,monoammonium glycyrrhizinate 0.5%,pH5.0,40℃,the conversion rate of monoammonium glycyrrhizinate reached 91.8%and glycyrrhetinic acid yield reached 83.5%after being converted for 72h by enzyme from Aspergillus niger.(2)The separation and purification process of glycyrrhetinic acid from the transformation products was investigated.D120 macroporous resin had the best separation effect for glycyrrhetinic acid among over ten kinds of resins by static adsorption and adsorption experiments.After the purification of D120 macroporous resin,the purity and the recovery rate of glycyrrhizic acid reached 77.6%and 81.85%,respectively.(3)On the basis of monoammonium glycyrrhizinate converted by Aspergillus niger,glycyrrhizic acid from licorice was transformed into glycyrrhetinic acid directly.The results showed that when Aspergillus niger was cultured in licorice solid medium for 5 days and proceed to transform for 2 days in buffer(pH5.0),the conversion rate of glycyrrhizic acid reached 97.67%,and the yield of glycyrrhetinic acid reached 71.84%.Compared with chemical transformation,biotransformation simplified the extraction process of glycyrrhizic acid and avoided the environmental pollution problems which was caused by extraction process,it was worthy of exploitation.(4)The structures of vitexin and breviscapine were modified by glucosyltransferase in this research.The results showed that vitexin and breviscapine were added one glucose residue to three glucose residues by glycosyltransferase.At the optimal conditions,the conversion rate of vitexin reached 61.80%,the yields of mono-,di-and tri-glucosylated vitexin were 38.36%,16.61%and 5.90%respectively,and the conversion rate of breviscapine reached 57.14%,the yields of mono-,di-and tri-glucosylated breviscapine were 34.96%,15.79%and 5.87%respectively.(5)By research of stevioside and phenolic acid content from different varieties of Stevia rebaudiana,the results showed that cultivar 4 contained the highest SS of 8.41%,cultivar 9 contained the highest RC of 1.7%,3,5-diCQA of 3.11%and 4,5-diCQA of 5.07%,cultivar 6 contained the highest RA of 13.67%,cultivar 2 contained the highest RD of 1.60%.