Study On The Preparation By Enzymatic Hydrolysis And Activity Of Xylooligosaccharides From Corn Cob

Xylooligosaccharides are oligasaccharides composed of xylose units linked by β-1,4-xyloside bonds with xylobiose and xylotriose as the main ingredients. It can be prepared by p-xylanase reaetion with corn cob, cotton seed hull or rapeseed hull. They are highly-effective bifid bacteria improver and have good physiological activities, and are widely studied all over the world. Due to the absence of a single constituent from xylooligosaccharides, the price of some products on the market is higher. So it is of great significance to seek a convenient preparation method of single component. This dissertation systematically studied the processing of the xylooligosaccharides production from corn cobs with enzyme, separation of single component of xylooligosaccharides, activity and its application in the yogurt.Firstly, the composition of con cobs was analyzed. The result indicated that crude fiber content, soluble sugar content, reducing sugar content, protein content, fat content, crude ash content, moisture, xylogen content of corn cobs were amounted to 43.34%±0.49%, 0.34%±0.01%,0.13%±0.01%,0.07%±0.01%,0.67%±0.02%,1.87%±0.03%, 12.06%±1.23%,28.47%±0.87%, respectively.The extraction processing of xylan from the corncob was established through single factor experiment and orthogonal test as the followings:corncob powder was mixed with 15% sodium hydroxide at the ratio of 1:15(w/v) and the mixture was heated to 85 ℃ for 150 min. Under this condition, the yield of corncob xylan was 12.43%.Xylooligosaccharides that wre prepared by enzymatic hydrolysis was analysed by the method of TLC and HPLC. The silica gel column chromatography was used to separate xylobiose and xylotriose from xylooligosaccharides. The purity of xylobiose and xylotriose are 90%-95%and their structures were analysed by HPLC, ESI-MS,’HCNMR,13CNMR and IR.The processing parameters of xylan hydrolysis by xylanase were optimized as the substrate concentration of 40 g/L, xylanase dosage of 0.02%, hydrolysis for 4 h. Under this condition, the yield of xylooligosaccharides was 89.61%.The experiment of promoting the discrepancy in bifidobacterium proliferation showed that activity of xylotriose was the best, followed by xylobiose and xylooligosaccharides. So the main active ingredients of xylooligosaccharides were xylobiose and xylotriose and the best bifidogenic factor was xylotriose.The optimum parameters of yogurt were derived by a series of parallel experiments and orthogonal experiments,0.45% xylo-oligosaccharide,7% sugar,3% inoculation,42℃ ferment temperature. The product which has physiological function and tasted well has been obtained. That has provided the reference for many milk companies’ new products.