Study On Ionic Liquid Extraction And Separation Technology Of Flavonoids And Proanthocyanidins From Citrus Peel And Grape Seeds

Natural active compounds including phenolics,alkaloids,amino acid,and bioactive peptides are attracting more and more attention in the field of food,biology,and medicine.Among these compounds,phenolics have significant bioactive activities,such as antioxidant,anti-inflammatory anti-bacterial,and anti-hypertensive activities.The byproducts of food-processing generally contain large amount of bioactive constituents.For example,citrus peel and grape seed are rich sources of phenolic compounds.Extraction,separation and purification are the important ways to obtain phenolic compounds with high purity,which will support the development and application of these bioactive compounds.However,traditional extraction methods always consume large amount of toxic organic solvent,have high cost of equipment,and pollute the environment.Ionic liquid?IL?,one of the promising and green solvents in 21 century,takes the advantages of high extraction efficiency and negligible volatility over conventional organic solvent.In the past two decades,ILs showed great potential in the field of extraction,separation,and purification.In this work,IL-based ultrasonic assisted extraction and aqueous two-phase extraction methods were developed in order to extract,separate,and purify the phenolic compounds in citrus peel and grape seed.Detailed contents of this work are summarized as following:1.Ionic liquids were applied to ultrasonic assisted extraction?UAE?of flavonoids in citrus peel.This work firstly compared extraction yields of two types of ionic liquid,namely cholinium-and phosphonium-based ILs.The phosphonium-based ILs showed much higher extraction yields than its counterpart,cholinium-based ILs.Among these studied ILs,P₄₄₄₄Br provided the highest yields of flavonoids?56.15mg/g?.Through single factor experiments and response surface analysis,the extraction conditions were optimized as following:IL concentration 54%,solid-liquid ratio 1:10,extraction temperature 50?,extraction time 10 min.Under the optimized conditions,the extraction yields of flavonoids from citrus peel reached 69.13 mg/g.After IL-UAE,backed extraction was performed for isolation of flavonoids and recycling of ILs.The results suggested that n-butanol was the most efficient back-extraction solvent,and the back-extraction efficiency of flavonoids achieved 80.11%.2.An aqueous two-phase system?ATPS?based on ethanol/?NH₄?₂SO₄ was proposed to extract and recover proanthocyanidins from grape seed.Ionic liquids?IL?were used as adjuvants of ATPS in order to improve the extraction performance.The extraction efficiencies of proanthocyanidins were dramatically raised from 47.89–52.42%to 97.23–97.79%by addition of 5 wt%[C₆mim]BF₄ into the ATPS.Extraction conditions were optimized as follows:29 wt%ethanol,19 wt%?NH₄?₂SO₄,4 wt%[C₆mim]BF₄,solid-liquid ratio 1:20 g/mL,temperature 40?,pH 5.0,and time20 min.Under the optimum conditions,the yields of catechin,epicatechin,and procyanidin B2 achieved 1.21,1.22 and 0.14 mg/g DW,respectively,with the extraction efficiency over 99.01%.In comparison with conventional organic solvents such as methanol,ethanol and isopropanol,the ATPS using IL as adjuvant provided much higher extraction yields.3.[C₄min]Br and[P₄₄₄₄]Br were selected as the representatives of ILs and used to construct ATPSs with five salts,including Na₂SO₄?K₂HPO₄?Na₂CO₃??NH₄?₂SO₄and K₃C₆H₅O₇.To study the partition behavior of phenolic compounds,the partition coefficients of three phenolic acids?chlorogenic acid,caffeic acid,and protocatechuic acid?and five flavonoids?vitexin,apigenin,hesperetin,hesperidin,and narirutin?in different ATPSs were determined and analyzed.The results suggested that the partition behaviors of phenolic compounds in ATPSs are affected by not only the salt types but also the pH values of ATPSs.Therefore,it is able to tailor the partition behaviors of phenolic compounds though selection of suitable salt and adjustment of pH values,which is beneficial to the improvement of high extraction selectivity and efficiency.