Preparation Of Modified Corn Bran Dietary Fiber By Enzyme Hydrolysis And Its Hypolipidemic Mechanisms

Maize (Zea. mays L.) is of Zea strain, a member of Graminaceae, Poaccae family. Corn bran is composed of aleurone, endosperm thick-walled tissue and seed capsule of Z. mays L.It is reported that corn bran has many physiological benefits such as mutagens adsorption, hypolipidemic effects, relaxation etc. In this dissertation, crude dietary fiber (CDF) was prepared from corn bran after the removal of most of starch and protein through enzyme hydrolysis. The influence of non-starch enzymes on the hypolipidemic function of CDF was investigated, and xylanase modified fiber (XMF) was abtained. The hypolipidemic mechanisms of XMF were then studied in a model animal system.The chemical composition of corn bran was analyzed and found to be as follows: TDF 65.38%, protein 10.32%, starch 17.50%, lipid 2.65% and ash 0.75%. The dietary fiber of corn bran was composed of cellulose (14.18%), hemicellulose (48.31%) and lignin (5.28%). In the corn bran, IDF and SDF content were 65.38% and 0.58%, respectively. The main composition of CDF was TDF (82.76%), protein (5.55%), starch (1.26%), lipid (2.04%) and ash (2.12%). The dietary fiber of CDF was composed of cellulose (18.82%), hemicellulose (50.57%) and lignin (8.15%). IDF and SDF content in CDF were 82.9% and 0.62%, respectively. CDF presented better acceptability of color, taste, texture and aroma than corn bran.Factorial experiments showed that there was no improvement for the binding capacity of CDF to bile salts in vitro through cellulase hydrolysis; the binding capacity of CDF to sodium cholate, sodium chenodeoxycholate, sodium deoxycholate and sodium taurocholate in vitro was increased to the highest level following xylanase hydrolysis. The effect of the combined treatment of cellulase and xylanase was better than cellulase alone but weaker than xylanase alone. Parameters of xylanase hydrolysis were optimized by response surface methodology, that is to say, hydrolysis pH of 5.3, hydrolysis time of 1.75 h and enzyme amount of 56 Iu/g CDF. The binding capacities of XMF to sodium cholate, sodium chenodeoxycholate, sodium deoxycholate and sodium taurocholate in vitro was 64.60, 48.34, 75.79 and 60.68μmol/ g XMF under the optimized conditions. There was no correlation between the bindings of any two bile salts by XMF, which indicates that the binding mechanisms of different bile salts by XMF studied here are different.The swelling capacity, water holding capacity and oil binding capacity of XMF were significantly higher than CDF (p<0.05). Additionally, SDF, IDF, TDF, cellulose and lignin content of XMF were also increased significantly (p<0.05). High performance gel filtration chromatography (HPGFC) analysis showed that the relative molecular weight distribution of S-XMF was mainly around 11588, which content was 1.64 fold of S-CDF, the part in S-XMF with relative molecular weight lower than 900 was only 62.6% of that in S-CDF. The neutral single sugar composition of XMF and CDF were studied through gas chromatography method. The main neutral sugar in I-CDF and I-XMF were xylose and arabinose, rhamnose in I-XMF was decreased to 44% of that in I-CDF. S-CDF and S-XMF were mainly soluble hemicellulose with high content of arabinose, xylose, mannose and glucose. In S-XMF, the mole content of every neutral single sugar was defferrent from S-CDF, and the content of arabinxylan was almost 10% higher than that in S-CDF. Soluble hemicellulose and arabinxylan can improve the hypolipidemic effects of XMF.X-ray diffraction and SEM results suggested that the amorphous region in XMF was decomposed partially, there were more big pores in XMF, which made the structure of XMF more out-of-order with larger capacity to bind water, lipids and bile acids.In rats with atherogenic diet induced hyperlipidemia, ingestion of XMF suppressed the increase of serum TG, TC, LDL-C and AI more significantly than CDF (p<0.05), and increased serum HDL-C level significantly at the same time (p<0.05). Furthermore, XMF significantly decreased epididymal fat, liver fat and liver cholesterol concentration more than CDF in rats (p<0.05), and then decreased the fat denaturation of liver cells.RT-PCR studies of several genes indicated that XMF could bind more chenodeoxycholate and deoxycholate than CDF in intestine, XMF enhanced the catabolism of lipids by up-regulating the expression of hepatic CYP7A1, FXR, PPARα, PPARγ, Lpl and Lpic, down-regulating the expression of ileal I-BABP and FXR. While CDF only down-regulated I-BABP expression, up-regulated hepatic PPARα, CYP7A1 and Lpl expression. Furthermore, XMF enhanced the excretion of lipid, cholesterol and bile acids more efficiently than CDF with significance (p<0.05). The antioxydation properties of CDF and XMF were also investingated in vivo. XMF ingestion could improve rats'antioxydation capability.For CDF and XMF, there were maximum adsorbing capacities against bile salts. There was no positive cooperation between the IDF and SDF parts in CDF during the adsorbing process of sodium cholate, sodium chenodeoxycholate or deoxycholate. There was somewhat cooperation between the two parts when adsorbing sodium taurocholate. However, the IDF and SDF parts in XMF presented strong cooperation when adsorbing the four bile salts. The main interaction between cholate and CDF/XMF was hydrophobic interaction. For CDF, the adsorption of sodium cholate and sodium taurocholate was completely competitive, sodium taurocholate was more competitive than sodium cholate; and the adsorption of sodium deoxycholate and chenodeoxycholate was partially competitive, the latter was more competitive than the former. For XMF, the adsorption of sodium cholate and taurocholate was non-competitive; while the adsorption of sodium chenodeoxycholate and sodium deoxycholate was partially competitive, sodium deoxycholate was more efficient than sodium chenodeoxycholate.The adsorption kinetics of the four cholates indicated that there were a larger adsorbing capacity and stronger adsorbing ability for XMF. Force measurements by AFM showed that both the interactions between XMF and sodium deoxycholate, XMF and sodium taurocholate were stronger than CDF.