Study On Enzymatic Preparation Of Peanut Peptides And Their Hypoglycemic Activity

Peanut is one of the important oil crops in China,which is rich in oil and proteins.However,compared with soybean proteins,peanut proteins are far from being widely used in the food industry.Peanut peptides with different biological activities can be obtained after peanut proteins are hydrolyzed by proteases.At present,there are many reports on the biological activities of peanut peptides such as antioxidant activity,hypotensive effect,and bacteriostasis,but whether peanut peptides have hypoglycemic activities in vivo is still unclear.In order to further develop the potential values of peanut proteins,commercial proteases were used to hydrolyze peanut proteins,and the α-glucosidase inhibitory activity of peanut peptides was measured.The optimal enzymatic hydrolysis conditions were obtained by enzyme species screening and response surface optimization.On this basis,peanut peptides were graded using ultrafiltration,and then the changes of enzyme inhibitory activity of peanut proteins,peanut peptides and peptide fractions with different molecular weights after simulated digestion in vitro were compared.In order to protect the biological activities of peanut peptides,liposomes were used to embed peanut peptides,and the optimum embedding conditions were optimized by orthogonal experiment.The model of type II diabetes mice was established,and the diabetic mice were fed with peanut protein,peanut peptides and their liposomes,and<1k Da peanut peptide fraction for 5 weeks,respectively.The body weight,blood sugar,organ index,serum lipid index,antioxidant capacity,and liver pathological sections of each group of mice were analyzed to further explore the hypoglycemic activity of peanut proteins and enzymatic peptides in vivo.The main findings are as follows:(1)Compared with other commercial proteases,peanut peptides prepared by trypsin had the highest α-glucosidase inhibitory activity although the hydrolysis degree was lower.The activities of peanut peptides prepared by trypsin further increased after heat treatment of peanut proteins(95℃,5 min).The enzyme inhibitory activity of peanut peptides was significantly positively correlated with their degree of hydrolysis in the range of 8.0% to 11.5%.The results of response surface experiment showed that the α-glucosidase inhibitory activity of peanut peptides was significantly affected by different factors in the order of enzyme amount > protein concentration > hydrolysis time.The optimal hydrolysis conditions were as follows: the amount of enzyme added was 2674 U/g,the protein concentration was 4.1%(w/v),and the hydrolysis time was 62 minutes.Under these conditions,the inhibition rate of peanut peptide(2 mg/m L)on α-glucosidase and α-amylase was 69.34±1.56% and 73.5±4.80%,respectively.The inhibitory activities of peanut peptides on these two enzymes were significantly higher than those of commercial soybean oligopeptides and casein peptides.(2)Four peanut peptide components with molecular weights >10 k Da,10-5 k Da,5-1k Da and <1 k D were obtained by ultrafiltration,accounting for 12.62%,9.47%,32.45% and45.46%,respectively,and the inhibitory activity of α-glucosidase were 76.38±0.42%,49.21±0.31%,19.94±0.39% and 17.23±0.31%.After artificial simulation in vitro digestion experiments,it was found that peanut proteins had enzyme inhibitory activity similar to peanut peptides after digestion by gastrointestinal fluid in turn.The enzyme inhibitory activity of the three peptide components of 10-5 k Da,5-1 k Da and <1 k Da was significantly increased after gastrointestinal digestion.The enzyme-inhibiting activity of peanut peptides after digestion only by intestinal fluid was increased by 5.6% compared with that when they were digested by gastric and intestinal fluids sequentially,indicating that the activity of peanut peptides in the process of gastric digestion was destroyed.(3)Peanut peptide liposomes were prepared by reverse evaporation method,and the embedding rate of peanut peptides was used as the index to optimize the prepation conditions.It was found that the significant effects of various factors on the embedding rate of liposomes ranged from the largest to the smallest: peanut peptides concentration > organic phase: internal aqueous phase > lecithin: cholesterol > cholesterol concentration.The optimum preparation conditions were lecithin : cholesterol 10:1,cholesterol concentration was 0.5 mg/m L,organic phase : internal aqueous phase was 4:1,and peanut peptide concentration was 2 mg/m L.The entrapment efficiency of the liposomes for peanut peptides prepared under these conditions was 78.10±0.28%,with an average particle size of 159.8±1.3 nm,and PDI of 0.24.(4)The diabetes mouse model was successfully established by high sugar and high fat diet combined with streptozotocin.The effects of peanut peptides and their liposomes,peanut proteins on various physiological indexes of mice were further explored.In terms of body weight,peanut peptides and theirs liposomes could increase the body weight of diabetes mice,while peanut proteins had no such function.In terms of blood glucose,the fasting blood glucose values of mice in the sample intervention group were consistently lower than those in the model control group,and the average blood glucose values of mice in the peanut peptide liposome group were consistently lower than those in the peanut peptide group at the same concentration,indicating that the former had better hypoglycemic effects,while peanut proteins showed similar hypoglycemic activity to peanut peptides.After the intervention of peanut peptides,the glycogen synthesis ability of mice was significantly enhanced and showed dose dependence.In terms of organs,compared with the model control group,the sample intervention group showed a lower organ index and sample dose dependence.Peanut peptide liposomes were more effective than peanut peptides in reducing the organ index and alleviating the degree of liver damage of mice.In terms of serum lipids,the contents of total cholesterol(TC),triglyceride(TG)and low density lipoprotein cholesterol(LDL-c)in serum of diabetic mice were decreased in different degrees after sample intervention,while the contents of high density lipoprotein cholesterol(HDL-c)was significantly increased.Compared with the peanut peptide group mice,the peanut peptide liposome group mice had lower TC content,higher TG and HDL-c contents,and similar LDL-c content.Peanut peptides could significantly lower the LDL-c content in mice compared to peanut peptide components with molecular weights <1 k Da at the same concentration.Compared with peanut peptide intervention,the decrease of TC and LDL-c in mice after peanut protein intervention was smaller,but the decrease of TG and the increase of HDL-c were greater.In terms of body antioxidant activity,the increase of superoxide dismutase(SOD)activity and glutathione(GSH)content in mice depended on the concentration of the intervention samples.Peanut peptide liposomes could enhance SOD activity more than peanut peptides,and peanut peptides could improve GSH contents and SOD activity more than the peanut peptide component with molecular weights <1 k Da and peanut proteins.Peanut peptides and peanut proteins can achieve the purpose of reducing blood sugar by improving the dyslipidemia and enhancing the antioxidant capacity of diabetic mice.