Antioxidant And Hypoglycemic Activities Of Mulberry Leaves Extract,Tea Polyphenols And Their Compounds

In this paper,the"Medicine and Food Homology"mulberry leaves extract?MLE?and the natural,efficient and safe tea polyphenols?TP?were systematically analyzed,including the physicochemical properties,composition,antioxidant and hypoglycemic effects,and drug interactions between MLE and TP.Then,the digestive characteristics of MLE,TP and their compounds were elucidated by constructing an in vitro oral-gastrointestinal digestive model,and the inhibitory effects of MLE,TP and their compounds on starch digestion and absorption were further studied,which provided theoretical basis for developing safe and effective natural functional products and related drugs for alleviating the diabetes.The main conclusions were summarized as following:1.The components of MLE and TP were analyzed.The contents of total carbohydrate,phenolics and flavonoids in MLE were determined by the method of Phenol-Sulfuric Acid,Folin-Ciocalteu and Aluminum Nitrate Complexation Spectrophotometry,and the composition of major polyphenols in TP was determined by high efficiency liquid chromatography.The results showed that the contents of total carbohydrate,phenolics and flavonoids in MLE was 24.69�0.31%,12.23�0.07%,and 20.1�0.36%,and the purity of TP was 97.91�7.21%.The major polyphenols found in TP are consisting of epicatechin?EC?,catechin?DL-C?,epigallocatechin?EGC?,epicatechin gallate?ECG?,gallocatechin gallate?GCG?and Epigallocatechin gallate?EGCG?,of which the content of EGCG was the highest,accounting for 42.57�2.41%.2.The antioxidant activities of MLE,TP and their compounds were determined.The concentration of half-maximal effect(EC₅₀)of MLE,TP and their compounds MLE:TP=1:1?m/m,the same as below?,MLE:TP=1:3 on DPPH free radicals were 0.088mg/mL,0.004 mg/mL,0.010 mg/mL and 0.008 mg/mL,and the EC₅₀ of them on ABTS⁺free radicals is 0.120 mg/mL,0.002 mg/mL,0.006 mg/mL and 0.003 mg/mL,respectively,and the antioxidant effects of them was TP>?MLE:TP=1:3?>?MLE:TP=1:1?>Vc>MLE.Application of the methods of Isobologram Equation and Median-effect Principle to study drug interactions between MLE and TP,to examine the antioxidant interaction of MLE-TP compounds,the results showed that the dose ratio points of the compound MLE:TP=1:1 and MLE:TP=1:3 were above the isoeffect lines,and the combination index CI of them were greater than 1,which indicated that MLE-TP compounds show antagonistic antioxidant effects.3.The hypoglycemic activities of MLE,TP and their compounds were determined.The hypoglycemic activities of MLE,TP and their compounds were evaluated by three key enzymes linked to diabetes:alpha-amylase,sucrase and maltase,and the acarbose was used as positive control.The 50%inhibiting concentration(IC₅₀)of acarbose,MLE,TP and MLE:TP=2:1 to alpha-amylase were 0.367 mg/mL,5.102 mg/mL,1.847 mg/mL and 1.707mg/mL,respectively.And the IC₅₀ of acarbose,MLE,TP and MLE:TP=1:1 to sucrase and maltase were 0.035 mg/mL,0.034 mg/mL,0.276 mg/mL,0.026 mg/mL and 0.051 mg/mL,0.036 mg/mL,0.087 mg/mL,0.023 mg/mL,respectively,and the compounds MLE:TP=2:1and MLE:TP=1:1 showed significantly better inhibitory effects on key enzymes than MLE and TP alone.Application of the methods of Isobologram Equation and Median-effect Principle to evaluate the hypoglycemic interaction of MLE-TP compounds.The results showed that the compound MLE:TP=2:1 show a synergistic inhibition on alpha-amylase,and MLE:TP=1:1 show the synergistic inhibitions on sucrase and maltase,indicating that the biological activity of the compounds of MLE and TP was closely related to their ratio.4.By simulating the oral-gastrointestinal digestive system in vitro,the digestive characteristics of TP were studied,and the changes of antioxidant and hypoglycemic activities of MLE,TP and their compounds during digestion were also investigated.The results showed that TP show a poor digestive stability in the upper digestive tract with great degradations for oral and upper small intestinal phase.Meanwhile,the antioxidant and hypoglycemic activities of MLE,TP and their compounds MLE:TP=2:1,MLE:TP=1:1 gradually decreased,among which the antioxidant activities significantly decreased for the oral phase and upper small intestinal phase,but the compounds MLE:TP=2:1 and MLE:TP=1:1 showed significantly better inhibitory effects on key enzymes linked to diabetes than MLE and TP alone during the digestive process?p<0.05?.In addition,starch as a model substrate,the inhibition rates of MLE,TP and their compounds MLE:TP=2:1,MLE:TP=1:1 on reducing sugar were35.93�2.64%,46.07�1.08%,58.45�1.54%and 56.92�0.71%after oral-gastrointestinal digestion,and the inhibition rates on glucose were 66.66�1.02%,51.40�1.35%,70.06�0.84%and 73.71�0.32%,respectively.Compared with the inhibitory effects of MLE and TP alone,the compound MLE:TP=2:1 and MLE:TP=1:1 showed more significant inhibitory effects on starch digestion and release of reducing sugar and glucose?p<0.05?,effectively reducing the production of reducing sugar and glucose in the digestive system.