Study On Extraction,Component Analysis And Stability Of Flavonoids From Jun Jujube Hotan

Xinjiang jujube is known for its high nutritional value and functions,rich in a variety of nutrients and bioactive components.In this thesis,five different methods were used to extract flavonoids,the bioactive substances in red dates,to compare the effects of extraction methods on total flavonoid content,flavonoid composition and their stability,to study the stability of rutin in deep eutectic solvents(DES),and to lay the foundation for the rational development and utilization of Xinjiang jujube,in particular,to provide theoretical reference for the in-depth study of the stability of jujube flavonoids.The specific research contents are as follows.1.Effect of different extraction methods on the yield of flavonoids in Xinjiang red jujube.Using Xinjiang Hotan Jun jujube as raw material,urea was identified as the hydrogen bond donor,choline chloride as the hydrogen bond acceptor,and DES as the extractant,and ultrasonic-assisted,microwave-assisted and enzymatic-assisted extraction were used for the extraction of flavonoids.The optimal extraction conditions for each extraction method were determined by single-factor and response surface optimization experiments.(1)Ultrasound-assisted DES extraction:molar ratio of DES systems 2:1,water content 45%,solid-liquid ratio 1:40 g/mL,ultrasonic frequency 35 kHz,ultrasonic temperature 70℃,ultrasonic temperature 70℃,ultrasonic time 44 min,the yield of flavonoids was 5.79 mg/g.(2)Microwave-assisted DES extraction:DES system molar ratio 1:3,water content 34%,solid-liquid ratio 1:42 g/mL,microwave power 700 W,microwave time 160 s,the yield of flavonoids was 8.03 mg/g.(3)Enzymolysis assisted DES extraction method:the molar ratio of DES system 1:3,water content 50%,solid-liquid ratio 1:45 g/mL,and compound enzyme 1(cellulase:Pectinase=2:1),enzyme addition amount 14.5 g/mL,pH 5.10,enzymatic digestion temperature 70℃,reaction time 3 h,then the yield of flavonoids was 6.85 mg/g.(4)Hot water extraction:solid-liquid ratio 1:45 g/mL,extraction time 70 min,extraction temperature 90℃,then the yield of flavonoids was 3.61 mg/g;(5)Ethanol extraction:ethanol concentration of 40%,solid-liquid ratio 1:24.5 g/mL,extraction time 48 min,extraction temperature 90℃,and the yield of flavonoids was 5.14 mg/g.There were significant differences(P<0.05)in the total flavonoid content of different extraction methods,among which the DES xtraction method was better than the traditional water extraction method and ethanol extraction method,especially the highest total flavonoid content was obtained by microwave-assisted DES extraction method.2.Effects of different extraction methods on flavonoids components and their stability.For the flavonoid extracts of jujube obtained by the above five extraction methods,the flavonoid components were identified and stability studies were studied.(1)The flavonoid fractions in hotan jujube were identified by liquid mass spectrometry(HPLC-MS),including rutin,catechin,vitexin,dihydromyricetin,quercetin 3-O-furanglucoside,dihydroquercetin,epicatechin,quercetin,dihydrokaempferol,luteolin,quercetin,naringin chalone,apigenin,kaempferol,isorhamnetin.The flavonoid components extracted by the five methods differed,and the highest content of rutin was found in the extracts of all methods.(2)Study on the stability of flavonoids.①After the crude extract of flavonoids was treated at high temperature for 2 h at 90℃ the crude extract of DES-sonication had the best thermal stability and the highest flavonoid retention rate of 98.15±0.51%.②The crude extracts of each flavonoid were stored at room temperature and protected from light for 21 d.The flavonoid extracts obtained by DES-sonication were the most stable during 21 d with the highest flavonoid retention of 64.25±2.21%,while the flavonoid extracts obtained by DES-enzymatic digestion were the least stable with only 30%residual.③After UV,natural light radiation and light avoidance storage for 44 h,respectively,UV light had the greatest effect on the crude extract of flavonoids,and the retention rate of flavonoids decreased the fastest;light avoidance storage had less effect on flavonoids,and the flavonoids extracted by DES-ultrasonic method was the most stable,with the highest retention rate of flavonoids of 86.44±2.45%.By comparing the stability of flavonoids of different extraction methods,DES-ultrasonic extraction method could protect flavonoids better,therefore,DES-ultrasonic is a more suitable method for extracting flavonoids of hotan jun jujube.3.Stability study of rutin simulation system based on DES.For rutin,the most abundant flavonoid in jujube,DES simulation system was constructed to study the stability of rutin.(1)The best DES system to stabilize rutin was determined as choline chloride-urea with a molar ratio of 1:2 and water content of 20%;the concentration of rutin was in the range of 0.28-0.68 mg/mL,and the solubility of rutin increased with the increase of heating temperature(30-80 0C).(2)With water as the solvent,the decrease in thermal stability of rutin at 60-90℃ after heating in it was all greater than in the rutin-DES system,indicating that rutin has better thermal stability in the DES system than in water.(3)The retention of rutin in different solvents decreased with increasing irradiation time.And the retention of rutin in DES was higher than that in water soluble method with the highest retention rate of 99.93%±3.37.(4)The retention rate of rutin dissolved in DES decreased to 44.15±1.10%after 57 d of rutin solution,while the retention rate of rutin in water soluble method was only 28.81±3.03%.During storage,the DES-dissolved rutin maintained better stability than the water-soluble method.This shows that the DES dissolution method has obvious advantages and plays an important role in improving the stability of rutin.