Inhibitory Mechanism And Microencapsulation Of Three Berry Anthocyanins On α-glucosidase

The diabetes mellitus has become the third serious diseases,next to cancer and cerebrovascular disease,especailly Type Ⅱ diabetes mellitus has caused a serious threat to human health.Recent studied showed that inhibiting alpha-glucosidase(α-glucosidase)activity is an effective way to prevent and alleviate diabetes mellitus.At present,the α-glucosidase inhibitors are mostly artificially synthesized,including acarbose,miglitol and voglibose,etc.Long term of administration of these inhibitors may cause side effects in human body,such as abdominal bloating and diarrhea.Therefore,it is promising to search natural products with good biocompatible as novelα-glucosidase inhibitors.Anthocyanins are important phenolic compounds,and widely distributed in berry fruits,with a variety of biological activities.However,relevant studies regarding the inhibitory effects of anthocyanins on α-glucosidase activity are limited.In this paper,three kinds of berries(blueberry,blue honeysuckle and blackcurrant)in northeast China were used as raw materials.The compositions of anthocyanins and its aglycones were studied by HPLC-MS.The inhibitory effects ofα-glucosidase by anthocyanin aglycones in three kinds of berries were then studied through kinetics,fluorescence quenching and molecular docking techniques.The biological activity of anthocyanin aglycones was protected by microencapsulation,which provided basis for the development of anthocyanin aglycones in health care products.The main results were described as follows:1.The components and contents of anthocyanins and anthocyanin aglycones in three kinds of berries(blueberry,blue honeysuckle and blackcurrant)in northeast China were analyzed by HPLC-MS.Thirteen,five and four anthocyanins were identified in blueberry,blue honeysuckle and blackcurrant,respectively.The anthocyanins contents were 13.75 mg/g DW in blueberry,15.70 mg/g DW in blue honeysuckle and 36.33 mg/g DW in blackcurrant,respectively.The anthocyanins of blueberry,blue honeysuckle and blackcurrant were acid-hydrolyzed to obtain the corresponding anthocyanin aglycones.Four,three and two anthocyanin aglycones were identified,respectively,among which delphinidin and cyanidin were the main components of anthocyanin aglycones.The anthocyanin aglycones contents were 2.74 mg/g DW in blueberry,2.28 mg/g DW in blue honeysuckle and 1.72 mg/g DW in blackcurrant,respectively.The anthocyanins were found mostly in the glycosylation form and connected with sugar moieties including galactoside,glucoside,arabinose and rutinoside at 3rd in the C ring.2.The inhibitory mechanism of anthocyanin aglycones in blueberry,blue honeysuckle and blackcurrant on α-glucosidase was measured by kinetics,fluorescence quenching and molecular docking.The IC50 values of anthocyanin aglycones in blueberry,blue honeysuckle and blackcurrant were 113.15 μg/mL.25.04 μg/mL and 5.59 μg/mL,respectively.The results of kinetics showed that the anthocyanin aglycones from three berries were mixed-type inhibitors,and the binding force with α-glucosidase was stronger than that of α-glucosidase-substrate(pNPG).The fluorescence quenching results showed that the inhibition was a static model.The molecular docking analysis revealed that the hydroxyl group on B ring of anthocyanin aglycones could inhibit the activity of α-glucosidase by forming hydrogen bonds with α-glucosidase residues.Therefore,the anthocyanin aglycones of the three berries had a strong inhibition effect on α-glucosidase,demonstrating that anthocyanin aglycones were potential natural phytochemical for preventing and alleviating diabetes mellitus.3.The anthocyanin aglycones were encapusled by drip method with sodium alginate as wall materials.The results showed that the encapsulation rate of anthocyanin aglycones was 75.61%when the sodium alginate concentration,calcium chloride concentration,inulin concentration,and core to wall ratio were 1.5%,3%,5%,and 1:4,respectively.SEM,FTIR,XRD and TG/DTG results showed that the microcapsules were made by the interaction of COO" from sodium alginate with Ca2+from CaCl2 to form chelates,yielding dense network structures on the microcapsule surface.The anthocyanin aglycones were embedded in microcapsules through physical interactions,no any chemical reaction involved.The stability tests proved that microcapsules significantly reduced the effects of light,heat and oxygen on anthocyanin aglycones,improved the stability of anthocyanin aglycones and kept its biological activity.During the simulated gastrointestinal tracts,it was observed that the release rate of the microcapsules was 50.56%after 2 h of digestion in the gastric juice.The microcapsules slowly released anthocyanin aglycones in the intestinal fluids,and the structures of the microcapusles completely collapsed after 2 h of digestion.It was suggested that the utilization rate of anthocyanin aglycones in the human intestinal tract was improved by encapsulation,and the inhibition against α-glucosidase activity in the small intestine may be therefore achieved.