A Preliminary Study On The Degradation Of Arabinoxylans Of Malt By Endo-?-1,4-xylanase During Mashing

Wheat malt is a great raw material for beer brewing,and it has a unique resource and price advantage in our country.At present,the wheat beer which is mainly made by wheat malt is particularly popular with consumers.Arabinoxylans is the principal non-starch polysaccharide that contented in the cell wall of wheat.As the endogenous enzyme degradation of Arabinoxylan is inevitable during the brewing process of wheat beer,the content and molecular size of the degradation products have a notable impact on the viscosity,turbidity,filtration speed,foam and body of the wheat beer.However,the enzyme degradation discipline of arabinoxylan in the wheat malt is still unclear.Therefore,this study intended to investigate the degradation regulation of wheat malt arabinoxylan by the endogenous and an exogenous endo-?-1,4-xylanas during mashing.It is also aimed to elucidate the content and molecular size of the product arabinoxylan,meanwhile the relashionship between the content and molecular size of the product arabinoxylan and the viscosity and turbidity of the wort were revealed.The main conclusions are as follows:(1)When the wort was rest at 40?and 45?for 10 min,the ?-1,4-endoxylanase activity was 1.12 u/g and 1.11 u/g,and there was no significant difference.While the wort was stopped at 52? for 10 min,the ?-1,4-edoxylanase enzyme showed inactivation.During wheat beer brewing,the saccharification resting temperature at 40?45?could be extended to enhance the effect of ?-1,4-endoxylanase.(2)In the conditions of the ratio of barley malt and wheat malt was 1:1,and the ratio of material to water was 1:3.5 and the pH of the mash was 5.88,the wort was rested at 40?for10 min,20 min,30 min,40 min,50 min,60 minutes,the activity of ?-1,4-endoxylanase growing primary and then falling.The enzyme activity was 1.40 u when the wort rest for 10 min,and reached the top value of 1.49 u at 30 min.When the rest time was extended to 60 min,the enzyme activity declined to 1.21 u.The turbidity of the wort was found to increase at the beginning and dropping in the end.Within the first 30 minutes,it was recorded a risen value of the wort turbidity from 21.2 NTU to 23.89 NTU,but it began to decrease after 30 minutes.The viscosity and turbidity showed a similar trend,as for 1.78 mPa·s at 10 minutes,1.86 mPa·s at 30 minutes,and reduced to 1.77 mPa·s at 60 minutes.(3)In the conditions of the ratio of barley malt and wheat malt was 1:1,and the ratio of material to water was 1:3.5 and the pH of the mash was 5.88,the wort was rested at 40?for10 min,20 min,30 min,40 min,50 min,60 minutes,the content of total arabinoxylan-oligosaccharides in the wort increased from 0.94?g/mL to 1.44?g/mL,among of which the xylotetraose,xylopentaose,and hexasaccharide had no significant difference.The content of xylotriose developed from 0.09?g/mL to 0.13?g/mL,and xylobiose presented a huge increase from 0.59?g/mL to 0.97?g/mL.The content of water-soluble arabinoxylan had risen with the interval in the first 30 min,from 1.63 mg/mL to 1.99 mg/mL,but declined to1.37 mg/mL at 60 min.Meanwhile,the degree of polymerization of the arabinoxylan progressed to 12.74 at first and then started to decrease after 30 minutes,finally to 11.45 at 60 minutes,A/X had an improvement from 0.60 to 0.62 throughout 10 to 30 min,then lowered from 0.62 to 0.55 throughout 30 to 60 min.There were four molecular weight components identified of the arabinoxylan in the wort,which was component I(>6200 Da),component II(1320?6200 Da),component III(242?1320 Da)and component IV(<242 Da).The foremost molecular weight range was 1320?6200 Da,which content rised from 1.17 mg/mL to 1.46mg/mL through the first 30 min,and declined to 1.03 mg/mL at 60 minutes.Besides,absolute content of the arabinoxylan of the molecular weight greater than 6200 Da had been shrinked,from 0.32 mg/mL to 0.17 mg/mL,and the relative content of which was reduced from 19.90%to 12.56%.The absolute content of the 242?1320 Da molecular weight segment had no significant difference.The relative content of the 242 Da arabinoxylan,had been risen from2.69% to 7.00%.(4)In the conditions of the ratio of barley malt and wheat malt was 1:1,and the ratio of material to water was 1:3.5 and the pH of the mash was 5.88,an ?-1,4-endoxylanase which originated from microbial source was added to the wort.It was found that after rest at 40?for30 minutes,the turbidity and viscosity of the wort had been declined,the viscosity was droped by 31.89%,and 28.80% of the turbidity.The content of arabinose and xylose both developed apparently.And the content of arabinose enhanced from 0.13 mg/mL to 0.67 mg/mL,and which of xylose increased from 0.12mg/mL to 1.02mg/mL.The content of water-soluble arabinoxylan showed a decreasing from 2.15 mg/mL to 1.25 mg/mL,and the degradation rate of arabinoxylan was 44.72%.There was a 25.98% decline in the degree of polymerization,but only a small relative change in the total content of oligosaccharides,which was originally0.97 ?g/mL,and increased to 1.01 ?g/mL.The addition of exogenous enzymes promoted the degradation of water soluble arabinoxylan.The arabinoxylan component with a weight average molecular weight of 1320?6200 Da played the main role in degradation,and its reducing proportion(from 1.46% to 0.81%)was exposed.In addition,there showed another significantly increase on the relative content of less than 242 molecular weight segment,which from 3.51% to 3.82%.