Research On Extraction,Purification Process Of Flavonoids In Waste Residue Of Stevia Rebaudiana And Its Antioxidant Activity

A large number of stevia waste residue discharged from the Stevia sugar production process would result in serious environmental pollution. The waste has many kinds of natural organic matters such as flavonoids which has great health-care function. The determination method, extraction and purification process of the flavonoids from the stevia waste residue were studied in this paper to research the feasibility of its recycling and provid a theoretical basis for the comprehensive utilization of the waste.The research included following aspects:(1)A spectrophotometric method for the determination of flavonoids content in Waste Residue of Stevia Rebaudiana was established by comparing the UV-Vis spectra with some spectrophotometric methods. The optimum conditions and its precision were also studied. The results showed that the best determination method was Na NO2-Al(NO3)3-Na OH. The standard sample was rutin and the wavelength was 500 nm. The method conformed to the Lambert-Beer’s Law in the ranges from 0.002 to 0.024μg?m L-1, correlation coefficient R2=0.9998, and recovery rate was between 96.0% and 104.3%. Its stability and repeatability were good.(2)The solvent used to extract the flavonoids from the waste was ethanol. Some factors which influence the extraction rate was studied and the optimum condition was selected by analyzing the single test and orthogonal test. The result was as follow: extracting the waste 2 times with 80% ethanol at 80℃, 1∶20 solid-liquid ratio and extraction time of 2h. Under this condition, the extraction rate of flavonoids was 0.62%.(3)The flavonoids extracted by ethanol was purified respectively by chitosan and polyamide. With the purity of flavonoids as the index, the optimum condition of the chitosan flocculation process was analyzed by single test and orthogonal test. The polyamide purification process was studied by analyzing the effects of The adsorption, desorption, adsorption kinetics and so on. The optimum condition and the regenerability was also researched. The result showed that the sample needed to stirred for 15 min with 1.0m L chitosan solution at 35℃and p H was 5. The concentration of the sample for absorption by polyamide was 0.2mg?m L-1 and the velocity was 1.5m L?min-1. The eluent was 60% ethanol and its velocity was 1.5m L?min-1. The purity were risen from 8.15% to 53.42%. The polyamide could be reused at least 6 times.(4) The chemical reaction, UV-Vis spectra, IR spectra were used to identificated the structure of the flavonids. The antioxidant activity of the purificatied flavonids was researched by compared with reducibility and free radical scavenging rate of ascorbic acid. The results showed that the main component was 5,7,3’,4’-dihydroxyflavnoe. The production had a strong antioxidant activity.This process further optimized the spectrophotometric condition on the determination of flavonoids content. The method, which was simple, rapid and accuracy, could be used in practical application.The study established a simple and efficient process with low-cost in the extraction step, and solved the problem of being hard to reuse the polyamide by the pretreatment of chitosan in the purity step. As a result, it reduced the cost greatly. This research provides a theoretical foundation for recycling residue of Stevia rebaudiana, realizing the reutilization of Stevia rebaudiana and environmental sustainability.