Changes Of Protein Composition During Wheat Malting And Beer Brewing With Different Addition Of Wheat Malt

Protein is one of the wheat storage materials; protein is the source of improve degrading enzyme activity during malting; protein is the important nutritional resource of yeast fermentation; protein is the fundamental material of influencing beer flavour and foam. The paper studied the content and molecular weight changes of protein compenents during malting, and the effects of wheat malt addition on protein content and molecular weight during brewing. The main conclusions were as following:1. During wheat malting, the alkali soluble protein began degrading at the steeping stage, and the prolamin started to degrade at the beginning of germination; the prolamin / alkali soluble protein decreases and the water soluble protein / salt soluble protein increases were sharp at the 2th of germination; water soluble protein content still changed during klining. Among these, the content of the 60 k Da water soluble protein decreased obviously, and the content of the 56 kDa, 44 k Da, 12 kDa- 15 kDa water soluble proteins increased. Compared with the wheat, the water soluble proteins content of the wheat malt increased by 181.0 %. The wheat and wheat malt also had different protein molecular weight distribution. The contents of the > 24.4 kDa and 9.8 k Da- 24.4 kDa water soluble proteins were relative high in wheat; the contents of the 2.5 k Da- 3.9 k Da and 0.4 k Da- 2.5 kDa water soluble proteins were relative high in wheat malt. The relative high molecular weight protein contents of salt soluble protein, prolamin and alkali soluble protein decreased. The contents of the 15 kDa- 71 kDa salt soluble protein decreased and the 11 kDa salt soluble proteins increased; the content of the 30 k Da prolamin decreased significantly; the contents of the 33 k Da- 100 kDa alkali soluble protein decreased.2. The protein contents of worts increased during mashing. Among these the protein content of the 100 % wheat malt wort was 459.18 % higher than that of the 100 % barley malt wort. The content of the > 2.2 k Da water soluble protein in the 100 % wheat malt was higher than that in the 100 % barley malt, especially the 4 kDa- 23 k Da water soluble protein. With the increase of mashing time, the 21 kDa- 71 kDa protein contents decreased, but the 38 k Da protein content increased gradually; the 4 kDa- 15 kDa protein contents increased. The > 15 kDa protein content had a decrease trend in 100 % barley malt wort and had no obvious change in 100 % wheat malt wort during mashing. The content of 0.6 k Da-2.2 k Da protein was relative high in malts, the corresponding values were 29.63 %- 35.97%;thecontentof2.2kda-15 kdaproteinwasrelativehighofworts,thecorrespondingvalueswere41.42%-45.10%.3. During fermination,the prote in contents of fermination broth decreased,especially decreased significantly at the main fermination stage.The protein content in the 100% wheat malt beer was 29.14% higher than that in the 100% barley malt beer.the 4 kda-15 kda protein content decreased obviously in the process of fermination;the 38 kda prote in content had no obvious change.with the increase of wheat malt amount,the >2.2 kda protein content in beer increased significantly.The content of the >15 kda protein in the 100% wheat malt beerwas 167.74% higher than that in the 100% barley malt beer.the >2.2 kda protein conten thad significan teffectson beer scharac teristics,especially the >15 kda protein content.the >15 kda protein content in beer swererel ativelow,buthad important effectson beer characteristics,suchas totalni trogencontent,turbidity,viscosity and soon.the >15 kda prote in was the keyprotein of wheat source in the beers of wheat maltaddition.