Inhibitory Effect Of Phenolics From Litchi Pericarp On ?-glycosidase And?-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.The?-glucosidase and?-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 on?-glucosidase and?-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 on?-glycosidase and?-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 of?-glycosidase with the IC₅₀ value of 11?g/mL and 112?g/mL,respectively,the IC₅₀value of?-Amylase were 0.5 mg/mL and 1.34 mg/mL.?2?Free and bound phenolics from litchi pericarp can reduce?-glycosidase and?-amylase endogenous fluorescence intensity with dose-effect relationship.The interactions between free and bound phenolics and?-glycosidase and?-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 of?-amylase.The free phenolics exhibited a strong static fluorescence quenching on?-glycosidase,while the bound phenolics displayed a static-dynamic quenching.The number of binding sites of both free and bound phenolics with?-glycosidase were one.The free and bound phenolic both dispalyed astatic-dynamic quenching on?-amylase,and the number of binding sites of?-Amylase were two.?3?Circular dichroism shows that with the increasing of the concentration of the free phenolic,?-helix of?-glycosidase and?-amylase increased,respectively,and?-fold,?-ture and random coil decreased.Meanwhile,bound phenolic decreased?-helix and?-ture of?-glycosidase,and increased?-fold and random coil;the?-helix and random coil of?-Amylase increase,while the?-fold,and?-ture wound decreased.The free and bound phenolic from litchi pericarp is able to change the secondary structure of?-glycosidase and?-Amylase,thus reduce the?-glycosidase and?-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 on?-glycosidase than?-Amylase.Procyanidins A₂ has the strongest inhibition on?-glycosidase while quercetin has the strongest on?-amylase.