Research About Protease During Wheat Malt And Malt Mashing

Our country has a big consumption for beer. With the improvement of people’s livingstandard and the change of consumer consciousness, the needs of the people for beer is nolonger just in quantity, the quality of beer and diversity also put forward higher request. Thewheat beer which has a lighter colority, a fresh taste and unique pure flavor was welcomedby more and more consumers and also has a broad development prospects. In the process ofbrewing, promoting the dissolution of the storage protein in malt is an important work. Thestorage proteins degradation of grain mainly happened in malt preparation. Though thesaccharification process is very short, the contribution of this step to the protein accountedfor one-third of the entire protein degradation. As the protease for protein degradation, theresearch of the role of protease in the brewing process also can indirectly reflect the proteindegradation. This paper regards wheat and barley as raw material, then determinate thepHysicochemical indexes of barley and wheat and the protease before and after germinationfrom the malting stage to the saccharification stage. And the paper analyses the wheatprotein degradation enzyme of different Kolbach index, protein composition andpHysicochemical indicators of malt from the finished product malt. And it determinates theimpact of the resting conditions of protein to the pHysical and chemical indicators ofprotease. The experimental results as follows:1The wheat malts’ basic properties, protein components, degradation enzyme activity,were evaluated. It was revealed that with the increase of Kolbach index, endoproteaseactivity had significant positive correlation with water-soluble protein and extract, r=0.732,0.727. While endoprotease activity had significant negative correlation with alcohol-solubleprotein r=-0.734. And there was a strong correlation between Aminopeptidase enzyme andsalt-soluble protein and endoprotease, r=0.735,0.764. This indicated that in the process ofprotein degradation, the peptide enzyme worked together with the aminopeptidase, whileaminopeptidase was a major role in the salt-soluble protein degradation. What is more,wheat malt Kolbach index had significant positive correlation with chromaticity, extract,FAN, acidity, r=0.971,0.880,0.915,0.964. And it had significant positive correlation withthe turbidity, r=0.714.2Protease activity of wheat mainly formed in the germination stage, and germinationpromoted the generation of protease. While germinating, the enzyme activity slowlyincreased to the maximum. In the following4d after steeping, with the time went by, the endoprotease enzyme activity was increased. And the maximum activity occurred on the4d,and then it fell. The aminopeptidase acitivity, on the other hand, increased with the timewent by. Adding gibberellin increased protease enzyme activity, but had no effect forenzyme change trend. There was a significant difference among aminopeptidase activity indifferent wheat varieties, while Endoprotease enzyme activity in different wheat varietiedbasically similarly.3Compare all kinds of protease in wheat malt and barley malt under different pH(4.7~6.8), the proteases changing trends are equal. As pH increases, the cysteine proteaseat pH5.0have biggest enzyme activity and then reduced, the ratio of metal protease, serineprotease in total enzyme activity gradually increased, aspartic protease proportion of totalenzyme activity decreases. Compared with wheat malt, barley malt drops off more sharplyunder the condition of high pH. Barley malt aspartic protease enzyme activity and the ratioof the total enzyme activity were lower than wheat malt. Increasing the pH, barley maltaspartic protease disappeared faster than wheat malt; Wheat malt metal protease is biggerthan barley malt metal class protease enzyme activity change. Therefore, improving the ratioof wheat malt metal protease has more potential than barley malt. While the pH increasing,the wheat malt and barley malt serine protease proportion are increased, and both of themneed high pH.4Controlling wheat malt and barley malt protein resting conditions (saccharificationtemperature, rest time, solid-liquid ratio and saccharification water pH), the saccharifyingwort is analyzed by physicochemical indicators and all kinds of protease, we found that asthe temperature increasing, wheat malt and wort chromaticity, FAN and total nitrogenincreased. Regardless of the wheat malt, barley malt, aspartic protease was not detected in55℃. At45℃, the barley malt has the highest activity. The wheat has the highest content in35℃, therefore, the optimum temperature of wheat cysteine class protease may lower thanbarley. But under45℃, wheat malt had the highest proportion for cysteine class protease.5The Solid-liquid ratio and the wort colority was reduced, the content of the total acidand the turbidity was increased. It might be that thick mash made a certain protective effectfor phenol enzyme. After the mash concentration was increased, the total protease activitiesof barly wort were increased and that of the wheat wort was reduced, and their metalprotease activities were both increased. The cysteine protease of wheat malt get themaximum protease activity in the ratio of1:3, and that of barley malt get the maximumprotease activity in the ratio of1:2. So the protection effect for enzyme of the higher concentration for the saccharification of wheat malt was lower than barley malt.6. Increase of protein resting time, chromaticity and pH increasing. While the restingtime at45min, the FAN and protein content have the maximum. Increase of protein rest time,barley wort and wheat wort aspartic protease activity reduced. Changing protein rest time,the barley wort cysteine protease enzyme have the highest activity at60min, the wheat wortcysteine protease have the highest activity at30min. Extend the protein resting time, theratio of wheat metallo protease increased gradually and the proportion of barley serineprotease reduced.7. Increase of saccharification water pH, the total acid increased. Because of the wortitself buffer, the pH did not increase significantly. No matter barley wort or wheat wort,while the pH from5.8to6.1, the FAN, extract and protein are reduced. Increase ofsaccharification water pH, all kinds of protease in barley wort and wheat wort reduce, buttheir changing trends are different. While saccharification water pH increased, no matterbarley wort or wheat wort aspartic protease and cysteine protease are reduced, but the ratioof aspartic class protease fall faster. While saccharification water pH at6.1, Barley wortaspartic protease did not appear. Increasing saccharifying water pH, both barley wort andwheat wort metal protease, serine proteinase ratio increased. Compare with wheat malt, theratio of barley malt metal protease growth faster. Therefore, it is suggested that wheat maltwort preparation process of protein resting stage and solid-liquid ratio decrease, the pHunder6.1, resting time45min temperature45℃is favour for wheat germ protein dissolved.