Effect Of Steam Explosion On The Physicochemical Properties And Hypoglycemic Activity Of Tartary Buckwheat Bran Dietary Fiber

Tartary buckwheat bran,a by-product of the processing of Tartary buckwheat,is high in annual output,low in price and rich in dietary fiber,which is a good source of dietary fiber.However,it is generally used as feed or fuel due to its rough taste,indigestibility and the low content of soluble dietary fiber(SDF),which greatly limits its application in the food industry,resulting in a great waste of dietary fiber resources.Steam explosion(SE)is a new method of dietary fiber modification in recent years,which can destroy the complex matrix of cell walls and modify the biological macromolecules through the instant release of high temperature and high pressure steam,compared with traditional modification methods,it has the advantages of high efficiency,low cost,economy and environmental protection,and has been gradually applied to the comprehensive utilization of agricultural products by-products.At present,type 2 diabetes mellitus(T2DM)has become one of the most serious metabolic diseases in the world.Many evidences have shown that dietary fiber supplementation can effectively prevent and alleviate T2 DM,especially grain dietary fiber has better hypoglycemic activity than other fruits and vegetables.As more and more attention has been paid to cereals dietary fiber and T2 DM,SE technology was introduced to modify Tartary buckwheat bran dietary fiber,and the effects of different SE conditions on the composition,physicochemical properties and structure of Tartary buckwheat bran dietary fiber were studied in this paper.Furthermore,db/db mice were used as the model of T2 DM to explore the effect of steam-explosive Tartary buckwheat bran SDF on hypoglycemic effect and its possible mechanism.The aim of this study is to provide theoretical reference for the further processing of Tartary buckwheat bran and the development of functional food of dietary fiber.The main conclusions are as follows:(1)The effects of different SE intensity on the composition of dietary fiber and other nutrients of Tartary buckwheat bran were studied.The results showed that the the SDF content of Tartary buckwheat bran significantly increased after SE treatment(P<0.05),which increased first and then decreased with the increase of SE intensity,and reached a maximum of 12.36 g/100 g at 1.2 MPa and 90 s,which was 55.74% higher than that ofTartary buckwheat bran without SE treatment.The IDF content of Tartary buckwheat bran decreased significantly(P<0.05)after SE treatment(except 0.9 MPa and 60 s),which was51.77% lower than that of Tartary buckwheat bran without SE under 1.2 MPa and 90 s.In addition,the content of cellulose,hemicellulose,and lignin in Tartary buckwheat bran significantly decreased after SE treatment(P<0.05),and decreased by 42.71%,54.94% and34.01% respectively compared with the non-SE treatment under 1.5 MPa and 120 s.The content of soluble sugar,reducing sugar and total sugar in Tartary buckwheat bran increased significantly after SE treatment(P<0.05),and increased 103.44%,32.55% and 12.39%respectively under 1.2 MPa and 90 s.(2)The effects of different SE intensity on the physicochemical properties of SDF and IDF of Tartary buckwheat bran were studied.The results showed that the water holding capacity,oil holding capacity and swelling capacity of Tartary buckwheat bran SDF significantly increased after SE treatment(except 0.9 MPa,60 s and 1.5 MPa,120 s),and reached its maximum under 1.2 MPa and 90 s,which was 69.00%,36.96%,and 36.38%higher than the Tartary buckwheat bran SDF without SE treatment,respectively,while the water holding capacity,oil holding capacity and swelling capacity of IDF decreased significantly(P<0.05).In addition,the inhibitory capacity of ?-amylase activity,glucose absorption capacity and in vitro fermentation capacity of Tartary buckwheat bran SDF and IDF were significantly improved after SE treatment(P<0.05),and the overall performance was optimal when the SE conditions were 1.2 MPa and 90 s,and the physicochemical properties of SDF were significantly higher than IDF(P<0.05).(3)The differential scanning calorimeter(DSC),Fourier infrared spectrometer(FTIR)and scanning electron microscope(SEM)were used to characterize the ultrastructure and physicochemical characteristics of Tartary buckwheat bran SDF and IDF under optimal SE conditions(1.2 MPa and 90 s).The results of DSC showed that the thermal stability of SDF and IDF of Tartary buckwheat bran increased by 7.35? and 9.26? respectively.The results of FTIR showed that the exposure of hydroxyl groups of SDF increased and some glycoside bonds broken after SE treatment,which may contribute to the SDF hydration property improvement.However,the hydroxyl groups and other functional groups of IDF of Tartary buckwheat bran moved red in a small range,and cellulose,hemicellulose and lignin may be partially degraded.SEM observation showed that after SE treatment,the surface of Tartary buckwheat bran was obviously broken,the particles were reduced,the pore structure and relative surface area of SDF and IDF were increased,and SDF hadhoneycomb network structure,which might be more helpful to the improvement of physicochemical properties of SDF.(4)db/db mice were used as a type 2 diabetes model to investigate the hypoglycemic effect of SE(1.2 MPa and 90 s)Tartary buckwheat bran SDF(SE-SDF).The results showed that SE-SDF treatment(1.5 g/kg,0.5 g/kg)could improve the blood glucose level of db/db mice,especially high dose SE-SDF(1.5 g/kg)treatment obviously improved the metabolic characteristics of polydipsia,polyuria and polyuria in db/db mice,and significantly reduced the index of liver,pancreas and kidney,significantly reduced the level of fasting blood glucose and glycosylated hemoglobin,improved the level of glucose tolerance and liver glycogen,improved the level of insulin resistance and dyslipidemia(P<0.05),and also significantly inhibited liver steatosis and pancreatic atrophy.In addition,SE-SDF could regulate the intestinal function of db/db mice,especially high-dose SE-SDF(1.5 g/kg)significantly increased the serum glucagon-like peptide 1(GLP-1)and fecal short-chain fatty acid content(acetic acid,propionic acid,butyric acid),as well as significantly reduced the level of serum lipopolysaccharide and obviously improved the damage of the colonic mucosal barrier in db/db mice.(5)The possible mechanism of hypoglycemic effect of SE-SDF was explored.The results showed that both high and low doses of SE-SDF(1.5 g/kg,0.5 g/kg)could promote the expression of PI3 K and FoxO1 protein in the liver tissue of db/db mice,and inhibit the protein expression of key gluconeogenesis enzymes PEPCK and G-6-Pase.In addition,high-dose(1.5 g/ kg)SE-SDF could also significantly promote the expression of GPR43 protein and phosphorylation of AMPK protein in liver tissue of db/db mice,and significantly increase the content of GPR43 protein in colon tissue of db/db mice(P<0.05).It is suggested that the mechanism of SE-SDF's hypoglycemic effect might be through the activation of the liver PI3K/AKt and SCFA-GPR43/p-AMPK signaling pathways to reduce liver insulin resistance and gluconeogenesis,and may also through the regulation of the intestinal health and blood glucose metabolism of db/db mice by activating the colon SCFA-GPR43/GLP-1 pathway,thereby exerting a hypoglycemic effect.