Component Analysis Of Alpha-amylase Inhibitor In Mulberry Residue And Its Hypoglycemic And Lipid-lowering Effects

Mulberry（Morus alba L.）is a medicinal and edible fruit with high nutritional value.It can be used as a supplementary food for lowering blood sugar and blood lipid.Mulberry residue,as a by-product of mulberry processing,still retains abundant active substances.As a reusable resource,mulberry residue has the advantages of low cost and high processing added value.Mulberry residue can be used to extract hypoglycemic and lipid-lowering active ingredients and compounded into nutritious healthy food with hypoglycemic and lipid-lowering effect.However,there are few reports on the extraction of mulberry residue.In this paper,Mulberry residue of"Big Ten"after juicing was used as raw material to study the treatment of raw materials,extraction and purification of active ingredients,and evaluation of hypoglycemic activity.The specific contents and results are as follows:Mulberry residue was pre-treated by hot air drying（50℃）and freeze-drying（less than 5%water content）.After ultrasonic extraction with different concentration of ethanol,the inhibitory activities of extracts on alpha-amylase were compared under different conditions.The results showed that the inhibition rate of hot air drying water extract on alpha-amylase was higher than that of freeze drying water extract,and the highest inhibition rate was 70.30%.Therefore,the optimum pretreatment method of mulberry residue is selected by hot air drying at 50°C,and ultrasonic assisted extraction with deionized water as extractant.With the inhibition rate of alpha-amylase as the evaluation index,the extraction conditions were optimized by orthogonal test.The results showed that the factors affecting the inhibition activity ofα-amylase were ultrasonic time>liquid-to-liquid ratio>ultrasonic temperature>ultrasonic power;The optimum extraction conditions were as follows:extraction time 1.5 h,solid-liquid ratio 1:40（g.mL-1）,ultrasonic temperature 50 C and ultrasonic power 300 W.Under these conditions,the inhibition rate of extract on alpha-amylase was 77.35%.With the inhibition rate of alpha-amylase as the evaluation index,the inhibitory activities of the extracts on alpha-amylase were compared after elution with five resins（AB-8,S-8,D101,NKA-9 and HZ-806）.The optimum resin type was selected,the separation and purification process of mulberry residue extract was optimized,and the components with inhibitory activities of alpha-amylase in ethanol eluents of different concentrations were analyzed by high-phase liquid chromatography.The results showed that AB-8 was the best resin,and the optimum technological conditions were as follows:sampling rate 1 BV·h^-1,70%（v/v）ethanol aqueous solution as eluent,elution flow rate 2.0 BV·h^-1.The content of quercetin was positively correlated with the inhibitory rate of alpha-amylase.The inhibitory rate of alpha-amylase in 70%ethanol eluent was 79.95%.The content of quercetin in this eluent was the highest,reaching 7.06 mg·mL^-1.The mice model of type 2 diabetes mellitus was established.Purified mulberry residue aqueous extract（PME）was given to mice at high and low doses(300 mg·kg^-1,100 mg·kg^-1)for 21 days.The results showed that compared with the model group,the blood sugar of PME group decreased significantly,the levels of total cholesterol（TC）,triglyceride（TG）,low density lipoprotein cholesterol（LDLC）decreased significantly,and the levels of high density lipoprotein cholesterol（HDLC）increased significantly.In addition,the content of malondialdehyde（MDA）decreased significantly and the level of superoxide dismutase（SOD）increased significantly in PME group,which indicated that PME had a significant protective effect on blood glucose and lipid,and could improve the body’s antioxidant capacity.Compared with the model group,the levels of AST,BUN and SCr in PME group decreased significantly,and ALT in low dose group（PMEL）decreased significantly,but ALT in high dose group（PMEH）decreased insignificantly.Scanning electron microscopic images of liver and kidney tissue sections showed that PME could protect the nucleus of diabetic mice and prevent steatosis.Therefore,PME could effectively protect the injured liver and kidney,and repair the steatosis of liver and kidney tissue and the infiltration of inflammatory cells.