| Alfalfa(Medicago sativa L.)is a perennial herb of the genus alfalfa in the family of papilionaceae alfalfa.It is the earliest used and most widely cultivated forage in the world.It is known as the "King of Forage" because of its high nutritional value.Alfalfa flowers are bright in color and rich in natural plant pigment-anthocyanins,which can be used as food colorant.In this study,the anthocyanins in alfalfa flowers were extracted by ultrasonic-assisted ethanol extraction method and purified by macroporous resin method.The composition of anthocyanins in alfalfa was identified by high performance liquid chromatography-tandem mass spectrometry,and the antioxidant capacity of anthocyanins in alfalfa was explored.Then,with maltodextrin xanthan gum acacia gum as the wall material,alfalfa anthocyanins were microencapsulated by freeze-drying,and the microencapsulation was characterized.The main research results were as follows:1.Based on the single factor test of liquid-solid ratio,ethanol concentration,extraction temperature and extraction time,using the anthocyanin content in alfalfa flower powder as the index,the extraction conditions were optimized according to the Box-Behnken combined experimental design principle and response surface methodology(RSM),the optimal extraction conditions of anthocyanins from alfalfa flowers were as follows:the ratio of liquid to material was 31 mL/g,the concentration of ethanol was 61%,the extraction temperature was 65?,the extraction time was 25 min,the ultrasonic power was 250 W.Under these conditions,the content of anthocyanin in the crude extract was 1.581±0.03 mg/g.2.Five kinds of macroporous resins,NKA-9,D101,AB-8,DM-301 and HP-20,were selected for the purification of anthocyanins from alfalfa,the results showed that D101 macroporous resin had better static adsorption and static desorption of anthocyanins in alfalfa,the adsorption rate was 56.53%± 1.45%,the desorption rate was 59.21%±1.82%;The results showed that the D101 macroporous resin reached adsorption saturation at 180 min,reached desorption completely at 150 min.Using ethanol as eluent,the optimal desorption conditions were as follows:the concentration of eluent was 40%,the pH of eluent was 2.0,the flow rate of eluent was 2 mL/min.The color value and content of anthocyanins of purified alfalfa were increased by 18.75 times and 7.4 times respectively.3.13 anthocyanin monomers,including 9 anthocyanins and 4 anthocyanin derivatives were identified by Fourier infrared spectrometer and High-performance liquid chromatography mass spectrometry.The 9 anthocyanins were cyanidin-3-sophoroside,cyanidin-3-feruloyl hexoside,petunidin-3-sophoroside,malvidin-3,5-dihexoside,cyanidin-3-malonylhexoside-5-hexoside,cyaniding-3-glucoside,cyanidin-3-malonylhexoside,petunidin-3-malonylhexoside,petunidin-3,5-dihexoside.Four anthocyanins were detected as anthocyanin glycosidic ligands:cyanidin,petunidin,peonidin and malvidin.The main anthocyanin monomers were cyanidin and petunidin.4.Using the maltodextrin,xanthan gum and gum arabic as wall materials,alfalfa anthocyanins were microencapsulated by freeze-drying method.There were significant differences in the embedding rate among different wall materials.Among them,the best wall material was maltodextrin:xanthan gum=30:1(w/w),and the embedding rate reached 98.37%±0.22%.Microencapsulated alfalfa anthocyanins showed better stability and better storage properties than unencapsulated anthocyanins,which provided a method for expanding the application of anthocyanins in alfalfa flowers.5.The antioxidant activity of anthocyanins in alfalfa flowers were studied in vitro.The scavenging rates of DPPH radical,ABTS+radical,hydroxyl radical and superoxide anion radical were determined.The results showed that when the concentration was 0.5 mg/mL,Alfalfa anthocyanins had certain scavenging ability on DPPH radical,ABTS+radical,hydroxyl radical and superoxide anion radical,and the scavenge effect of the purified anthocyanins was better. |
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