Inhibitory Effect Of Phenolics From Litchi Pericarp On α-glycosidase Andα-Amylase And Their Underling Mechanism

With the accelerating rhythm of life,the incidence of diabetes continues to rise in recent years.Among the diabetes,most of them belongs to type II diabetes,and their blood sugar can control without insulin.Theα-glucosidase andα-amylase inhibitor are the preferred drug to regulate postprandial blood glucose level.Therefore,the enzyme inhibition extracted from plant has gained great attention by the field of food researchers.The litchi production of our country ranked the first in the world,which will produce large amount of by-products such as litchi pericarp in the process of processing.Studies have shown that litchi pericarp is rich in phenolics,the existing research mainly focused on antioxidant activity,the improvement of atherosclerosis and so on,while its hypoglycemic is rarely reported.In the present study,we separated and extracted free and bound phenolics from litchi pericarp,studied its inhibitory effect onα-glucosidase andα-Amylase.The related mechanism was also studied.These results can provide scientific guidance and theoretical basis for the development of litchi by-product processing and utilization.The main contents and conclusions in the thesis are summarized as follows:（1）The free and bound phenolic from litchi pericarp has a obvious inhibitory effect onα-glycosidase andα-amylase.The inhibitory modes all belonged to a mixed type of inhibition.Our results showed that both of free and bound phenolics from litchi pericarp inhibited the activity ofα-glycosidase with the IC₅₀ value of 11μg/mL and 112μg/mL,respectively,the IC₅₀value ofα-Amylase were 0.5 mg/mL and 1.34 mg/mL.（2）Free and bound phenolics from litchi pericarp can reduceα-glycosidase andα-amylase endogenous fluorescence intensity with dose-effect relationship.The interactions between free and bound phenolics andα-glycosidase andα-amylase caused red shift（5±1 nm）and blue shift（4±1nm）of maximum emission wavelength;while free and bound phenolics maked red shift and blue shift（5±1 nm）of maximum emission wavelength ofα-amylase.The free phenolics exhibited a strong static fluorescence quenching onα-glycosidase,while the bound phenolics displayed a static-dynamic quenching.The number of binding sites of both free and bound phenolics withα-glycosidase were one.The free and bound phenolic both dispalyed astatic-dynamic quenching onα-amylase,and the number of binding sites ofα-Amylase were two.（3）Circular dichroism shows that with the increasing of the concentration of the free phenolic,α-helix ofα-glycosidase andα-amylase increased,respectively,andβ-fold,β-ture and random coil decreased.Meanwhile,bound phenolic decreasedα-helix andβ-ture ofα-glycosidase,and increasedβ-fold and random coil;theα-helix and random coil ofα-Amylase increase,while theβ-fold,andβ-ture wound decreased.The free and bound phenolic from litchi pericarp is able to change the secondary structure ofα-glycosidase andα-Amylase,thus reduce theα-glycosidase andα-amylase active site and reduce its activity.（4）The qualitative and quantitative analysis of free and bound phenolic compounds were performed by UPLC-Q-TOF/MS.Our results showed that free phenolics from litchi pericarp contained quercetin,rutin,salicylic acid,kaempferiae-3-O-glucoside,catechins,kaempferiae-3-O-rutinoside,procyanidins A₂.The content of procyanidins A₂ was the highest.Bound phenolic contained quercetin,kaempferiae-3-O-rutinoside,salicylic acid,orientin,gallic acid,vanillic acid,Gentisic acid,the content of orientin was the highest.These phenolics had a stonger inhibitory activity onα-glycosidase thanα-Amylase.Procyanidins A₂ has the strongest inhibition onα-glycosidase while quercetin has the strongest onα-amylase.