Study On The Functional Properties Of Arabinoxylan And Its Application

Whole meal foods are rich in dietary fiber, vitamin, minerals and various phytonutrients. Regular consumption of whole meal food will reduce the incidence of multiple chronic diseases. Whole meal bread as the staple food in western countries, is the best way to supplement the dietary fiber and a variety of nutrients. In our country, the coarse structure of whole meal bread leads to poor acceptance of the consumer and tremendous restrictions of the consumption. Gluten protein, arabinoxylan (AX) and their interactions have great influence on rheological properties of the whole meal dough and quality of the whole meal bread. The texture of whole meal bread can be improved and national health can be siginificantly enhanced by studying the functional properties of AX, which has important theoretical and practical value.In this paper, whole wheat flour was used as material, the extraction process of water unextractable arabinoxylan (WUAX) was optimized, and the high purity water extractable arabinoxylan (WEAX) and WUAX was obtained. The oxidative gelation mechanism of WEAX and WUAX as well as the interaction between gluten protein and AX was studied.The relative weight-average molecular weight of extracted WEAX is 414, 459 and WEAX is composed of 42.60% of arabinose, 51.55% of xylose, 3.89% of glucose and 1.96% of mannose. WEAX contains 0.25% of ferulic acid (FA), which play an important role in the functional properties of WEAX. The pretreatment results of extraction of WUAX by Ba(OH)2 showed that high-pressure treatment can increase extracion yield of the WUAX and content of WUAX in the extract as well. The optimum conditions of extracting WUAX by Ba(OH)2 are as follows: WUS (the water unextractable substance that removed protein and starch):Ba(OH)2 is 1:188(w/v), the extraction temperature is 63°C, the extraction time is 3h, the extraction rate is 31.60%. Variance analysis showed that the yield factors model was significant (P<0.05), and the square of the extraction temperature highly significant (P<0.001). Under optimum conditions, WUAX contents in the extract is 92.09%.Laccase (LAC) increase the viscosity of AX more obviously comparing with POX/H2O2, LOX/LA and chemical oxidants KBrO3, azodicarbonamide(ADA), benzoyl peroxide (BPO) and (NH4)2S2O8. When added LAC, the average weight molecular weight increased most obviously, which indicated that LAC can catalyze oxidation crosslinking more efficiently. By adding LAC, the FA of AX decreased more, which indicated that more FA involved in the oxidative cross-linking of AX. The free FA was added in the mixture of AX and LAC, the content of free FA in the mixture was measured after 1 h reaction. The results show that the free FA decreased and participated in the oxiditave cross-linking of AX, which means that AX cross-link through FA. When fumaric acid was added in the mixture of AX and LAC, concentrations of FA was almost no change, which indicated that the site of oxidation of AX was not double bond of FA structure. While by adding vanillic acid, FA in the solutions reduced and and with the increasing concentration of the vanillic acid, FA reduces more. To draw a conclusion, the site of oxidative crosslinking of AX was benzene ring and not double bond.Studies on the effect of WEAX and WUAX on viscoelasticity of gluten by combination of creep tests and dynamic small amplitude oscillatory measurements showed that WEAX and WUAX can significantly increase the viscoelasticity of gluten. When NaCl concentration was 4.0% (w/v), gluten and gluten-WEAX mixtures (G-WEAX) showed the largest viscoelastic. The gluten-WUAX mixtures (G-WUAX) showed the maximum elasticty at 3.0% (w/v) NaCl concentration and the maximum viscosity at 4.0% (w/v) NaCl concentration.The viscoelasticity of gluten, G-WEAX and G-WUAX reached the maximum at 50% water level. The free sulfhydryl of LMWG obviously reduced by adding WEAX and WUAX, which is one of the reason that the viscoelasticity gluten was increased by adding WEAX and WUAX.The fluorescence anisotropy measurements of gliadin and glutenin by adding AX showed that anisotropy value of glutenin significantly increased when AX was add in, indicating that AX interacted with glutenin.The ineractions of gluten proteins and G-AX determined by 13C NMR spectrum showed that the glutenin absorption peaks at chemical shift (δ) 136.5 and 128.8ppm (both were the absorption peaks of benzene ring) shifted to 137.6ppm and 129.9ppm, respectively by adding WEAX and shifted to 137.8ppm and130.1ppm, respectively by adding WUAX. For gliadin, there was no chemical shift by adding WEAX or WUAX. The results indicated that AX interacted with glutenin by covalently bond FA to tyrosine of glutenin.Studies on the effect of LAC, POX/H2O2 and LOX/LA on dough rheological properties showed that LAC most significantly improved the ordinary and the whole meal dough viscoelasticity and more significantly improved the viscoelasticity of the latter. The results of synthetically evaluation of the quality of ordinary bread and whole meal bread showed that the volume of whole meal bread is less than ordinary bread. When added to LOX and LAC, the volume of whole meal bread was significantly increased, and more obviously increased by adding LAC. When added by LAC, the average score of organizational structure of the bread section, mouth feeling and flaver of the whole meal bread increased more than that of the control, which means LAC can obviously improve texture of whole meal bread.Elasticity and hardness measurements showed that by adding LOX and LAC hardness of ordinary bread and whole meal bread reduced and elasticity increased comparing with control with LAC leading to more hardness reduce and elasticity increase. When adding LAC, changes of hardness and water content of whole meal bread and ordinary bread was the least.