The Preparation Of Xylooligosaccharide From Rice Husk Pretreated With Steam Explosion And Its Application In Cookies

China is a major country in rice production in the world.Rice husk,the by-product of rice processing,is abundant in resources.However,currently,the biological utilization rate of rice husks is low.Finding new ways to utilize rice husk and increasing its added value is an urgent problem that needs to be solved.Rice husk is rich in xylan.Xylan can be hydrolyzed into xylooligosaccharide(XOS)by xylanase.XOS is a functional oligosaccharide.Its physicochemical properties are stable,and it has the physiological functions of improving gut microbial flora,regulating blood glucose,etc.Extracting XOS from rice husk is high value approach to use rice husk.In this paper,rice husk was used as raw materials,steam explosion(SE)pretreatment was used to assist in xylanase hydrolysis to extract XOS.Anion exchange resin and ultrafiltration were used for purification.The structure and functional characteristics of the purified XOS were studied,and the effect of XOS addition on flour and dough characteristics was explored,as well as the quality of cookies.The main conclusions were as follows:The preparation of XOS from SE rice husk by enzymatic hydrolysis was studied.The results showed that SE destroyed the lignocellulosic structure of rice husk,and the XOS content significantly increased after enzymatic hydrolysis of rice husks pretreated with SE.Especially at 2.4 MPa,the extraction rate of XOS was the highest.SE is an efficient auxiliary method for XOS production.It was found that the optimal conditions for extracting XOS were the xylanase addition of3000 U/g,hydrolysis time of 3 h,and hydrolysis temperature of 50℃ by using single factor experiments and response surface methodology.Under these conditions,the XOS content was 150.90 mg/g.The purification process of XOS enzymolysis solution was studied,and the structure and functional properties of XOS after ultrafiltration were studied.The results showed that D301 anion exchange resin had good decolorization effect.Under resin addition of 40 g/L,decolorization time of 3 h,decolorization temperature of 50 ℃,initial pH 5,the highest decolorization rate was 78.70%.The structural analysis of XOS showed that the main signal and displacement of XOS were attributed to β-type xylose,with a small amount of α-type xylose.The purified XOS had high thermal stability.XOS had good antioxidant activities.When the concentration of XOS was 1.0 g/L,the scavenging rate of ABTS free radicals reached 99.34%.The purified XOS had a proliferative effect on four probiotics: Lactobacillus plantarum,Lactobacillus brucelli,Lactobacillus acidophilus,and Lactobacillus rhamnosus.The effects of XOS addition on flour and dough characteristics were studied(the addition amount was 1%,3%,5%).The results showed that: with the increase of XOS content,the gelatinization temperature of flour increased,and the breakdown value decreased,indicating that XOS inhibited starch gelatinization and weakened starch retrogradation.With the increase of XOS,the water absorption and weakening degree of flour showed a decreasing trend,the tensile area and resistance of dough also decreased.G ’and G’’ first increased and then decreased,resulted in a decrease in dough elasticity.Indicating that XOS inhibited the formation of gluten network structure.The peak ratio of strongly bound water and free water in 5% XOS dough decreased,while the proportion of weakly bound water increased,indicating that the water that was deeply bound to gluten protein decreased,which was not conducive to the formation of gluten network,and the viscosity of dough increased.Therefore,XOS was suitable for adding to flour to make cookies.The effect of XOS on cookie quality was studied.The results showed that the cookies made by adding XOS to flour had larger diameter,lower thickness,darker color,lower hardness,higher storage stability,higher antioxidant and antidigestion properties.XOS cookies had higher crystallinity and density than control cookies,resulted in lower digestibilities and eGI values.The addition of XOS increased the ester content and enhanced the flavor of cookies.The addition of XOS significantly improved the antioxidant activities of cookies(P<0.05).Based on the quality and antioxidant index of cookies,when the XOS content was 5%,the cookies had low hardness,good taste,good color,good storage stability,low eGI value and good antioxidant activities.