Study On The Cholesterol-Lowering Activity Of Dietary Fibre Extracted From Millet Bran

Millet bran(MB)is the main by-product in the process of millet production and processing.Though,its nutrition components are rich,it has not been fully exploited and utilized.Dietary fibre was the key component of MB and has been proved to have some physiological functions such as decreasing blood lipid,reducing blood glucose and bowel cancer risk and boosting immunity,et al.Therefore,the dietary fibre isolated form MB was modified by enzymes to improve its cholesterol-absorption capacity.What's more,the mechanism of cholesterol-lowering capacity of dietary fibre in vivo and in vitro was further studied.The main study contents are as follows:1.Extraction and absorption capacities in vitro of dietary fibres from millet bran.After determining that heat stable a-amylase and neutral protease were good for extracting dietary fibre from MB,enzymatic dietary fibre(E-DF)and enzymatic-chemical dietary fibre(EC-DF)were prepared by enzymatic digestion and enzymatic-chemical method,respectively.The yield of E-DF(72.20%)was almost twice higher than that of EC-DF(44.97%),although sacrificed a little in purity(about 2.5%lower than EC-DF).What's more,compared with MB,there were fewer starch grains and protein particles in E-DF showed by the SEM photographs.E-DF had sheet structure and mainly consisted of hemicellulose(47.83%)and cellulose(17.3%).Therefore,E-DF was used for further functional research.Results revealed that the water holding capacity and swelling power of E-DF were 3.24 g/g and 2.06 mL/g,respectively.Meanwhile,E-DF exhibited good adsorption capacities for liposoluble components such as lard(3.34 g/g),oil(2.32 g/g)and cholesterol(5.91 mg/g in pH 7.0).Its bile salts adsorption capacity(143.03?mol g-1 for sodium cholate and 76.65 ?mol/g for sodium taurocholate)indirectly reflected its cholesterol-lowering effect.Besides these properties,E-DF had high adsorption capacities for NO2-and Cation as the same.All of these results explained that the dietary fibre isolated from MB by enzymatic digestion method had great physiological functions and was a meaningful substance for research.2.Effect of enzymatic treatment on the cholesterol-absorption capacity of dietary fibre from millet bran in vitro.The dietary fibre prepared from millet bran by enzymatic digestion method(E-DF)was modified with cellulase and xylanase to improve its cholesterol-absorption capacity in vitro.Based on one-factor-at-a-time experiments,a L9(34)orthogonal array design was employed to optimize respective process parameters.The optimal enzymatic treatment conditions were as following:pH 3.8,the amount of cellulase 140 U/g,temperature 55? and treatment time 3 h and then the amount of xylanase 70 U/g,temperature 50? and treatment time 2 h.Under above conditions,the cholesterol-absorption capacity of enzymatic modified dietary fibre(EM-DF)was 15.66 mg/g,and increased by 1.64 times over the untreated E-DF(5.91 mg/g).The physicochemical studies on E-DF and EM-DF such as monosaccharide compositions,FTIR spectrum,molecular weight,crystal structure and microstructure demonstrated that the enzymatic treatment changed the saccharide composition of E-DF,and produced more cellobiose.Compared with E-DF,EM-DF was rougher and bearing more hydrophobic groups,and produced more SDF whose molecular weight was around 1.99×105 Da.To some degree,the crystal structure of E-DF was damaged.These physicochemical changes might closely relate to the high cholesterol-absorption capacity of EM-DF in vitro.3.The cholesterol-lowering capacity and molecular mechanism of the enzymes modified dietary fibre in vivo.Animal experimental results showed that,compared with the hyperlipidemia control group,the weight and the concentration of serum LDL-C of mice decreased significantly(P<0.05)after consuming E-DF or EM-DF for five weeks.Meanwhile,dietary fibre improved the content of serum HDL-C.And,the concentration of serum TC reduced 0.62 mmol/L and 1.03 mmol/L through eating the special fodder adding E-DF or EM-DF,respectively.These changes in blood lipid indexes suggested that EM-DF had greater cholesterol lowering ability than E-DF in vivo.RT-qPCR studies indicated that induction of high fat forage could down-regulate the expression of hepatic CYP7A1 and FXR.This might because that the hepatic steatosis disordered of lipid metabolism.Comparing with the results of hyperlipidemia control group,the E-DF and EM-DF boosted the cholesterol conversion by enhancing the expression of hepatic CYP7A1 and inhibition the expression of hepatic FXR.Also,EM-DF was more effective in lowering cholesterol in vivo.