Characteristics Of Wheat Malt LOX And Lipase In Malting And Saccharification

In the process of beer brewing, beer aging is paid more and more attention. As a mainsubstance, the cause of trans-2-nonenal is widely studies by researchers. Trans-2-nonenalwhich is formed by the enzyme reaction of a series of peroxide is hidden in beer.Trans-2-nonenal is released slowly during the shelf life and gives beer cardboard aroma. Thispaper studied enzymatic properties of Lipase and LOX, and also studied changes of enzymeactivity during malting, mashing etc.. The main studies were as follows:（1） Optimal temperature of LOX was35℃; optimal pH was5.5; thermal stability wasgood at4⁶0℃, which activity still keep114.86%,102.90%and93.37%when incubated60min at35℃,45℃and55℃correspondingly; the activity was decreased obviously at65℃,dropped by97.17%when incubated60min. When incubated5min at70℃, the enzyme wasinactive. LOX was stable at pH5.5⁶.0; When incubated10min at pH3.0, the activity was6.29%. When incubated50min at pH5.5, LOX was stable, and when incubated90min, theactivity was60.56%. Fe²⁺could strongly active LOX, and the activity increased by33.07%;Fe³⁺had a weak activation, and the activity only increased by11.28%. Cu²⁺, Mn²⁺, Mg²⁺, Al³⁺,Ca²⁺, Ba²⁺could inhibit LOX activity, of which Mn²⁺had an obvious inhibition and theactivity dropped by55.64%. EDTA had an inhibition on LOX, and the activity dropped by22.28%.（2） The activity of original wheat was56.90u/g; the activity was69.08u/g aftersteeping. During germination, the activity increased gradually; the enzyme activity reached amaximum at the third day, it was336.24u/g, and then the enzyme activity decreased; theenzyme activity did not change significantly at the forth, fifth and sixth day. After drying, theactivity was77.00u/g, and the rate of inactivation was74.33%. The enzyme activity of kernel,radical, embryo decreases in turn, respectively58.81u/g,14.34u/g,7.60u/g. During EBCmashing, the enzyme activity in malt without embryo was higher than that in malt. In theprocess of mashing, the activity of LOX decreased slowly before incubated30min at45℃,and the rate of inactivation was38.78%when incubated30min. The rate of inactivation wasobvious when incubated it from30min to55min at70℃. When removed embryo, the enzyme activity of LOX decreased obviously in the process of mashing. Whether removed embryo ornot, the enzyme was inactive when incubated50min. In order to reduce negative influence ofLOX, we should choose a Kolbach index below37.6%or above39.5%. TBA value rangedfrom31.4%to54.2%, and the value increased with the Kolbach index. TBA value hadsignificant positive correlation with the Kolbach index（r=0.951, P <0.01）. We shouldchoose a Kolbach index below37.6%in order to low TBA value and LOX value, butconsidering malt conventional index, we had better to choose37.0%. When malt startedmashing from different temperatures, the activity had different changes. The rate ofinactivation was only8.26%when incubated30min at35℃, and the activity was0.36u/mLwhen reached70℃, the rate of inactivation was94.59%, when incubated2min at70℃, theenzyme was inactive; The rate of inactivation was28.21%when incubated30min at40℃,and the activity was0.48u/mL when reached70℃, the rate of inactivation was91.79%, whenincubated2min at70℃, the enzyme was inactive; The rate of inactivation was57.04%whenincubated30min at45℃, and the activity was0.00u/mL when reached70℃, the rate ofinactivation was100.00%; The rate of inactivation was28.21%when incubated30min at50℃, and the activity was0.48u/mL when reached70℃, the rate of inactivation was91.79%,when incubated2min at70℃, the enzyme was inactive; The rate of inactivation was57.39%when incubated30min at55℃, and the activity was0.00u/mL when reached70℃, the rate ofinactivation was100.00%.（3）Lipase optimum temperature was37℃; optimum pH was4.0; thermal stability wasgood between4℃and35℃, its vitality retention rate were88.37%and46.81%respectivelyat35℃and45℃for60min, Lipase activity decreased obviously at45℃and enzyme activitywas46.81%of the blank for60min; Lipase inactivated rapidly at55℃and enzyme activitywas zero in60min; in65℃and70℃, Lipase inactivated more quickly, at65℃, Lipaseactivity was reduced to12.61%in1min and enzyme activity had been inactivated about6min; at70℃, Lipase activity was reduced to9.09%in1min, and enzyme activity had beeninactivated about5min. pH5.5and pH6.0had quite small destructive power to Lipase, andLipase activity remained95.11%and91.11%respectively for60min; Fe³⁺had stronginhibitional effect on Lipase, it could make Lipase enzyme activity drop to54.95%; Cu²⁺,Mn²⁺and Al³⁺had weaker inhibitional effect on Lipase, and made enzyme activity drop to80.68%,92.77%and89.74%respectively; EDTA had strong activation to Lipase, and enzymeactivity increased to110.53%. （4） Lipase enzyme activity of wheat was2.17u/g; after steeping, malt Lipase activitywas1.77u/g, but at the beginning of germination, Lipase enzyme activity increased obviously,from the first day to the fourth day, enzyme activity increased gradually and reached to themaximum8.52u/g on the fourth day. On the fifth day, enzyme activity started to decrease, onthe fifth day and sixth day, enzyme activity did not have obvious change. Because ofhigh-temperature drying, some Lipase in finished malt inactivated, inactivation rate was27.06%, enzyme activity decreased to4.66u/g. Lipase enzyme activity had significantdifference in different part of wheat malt, enzyme activity in malt kernel was the largest of8.01u/g; in germ it was7.55u/g; in radicle it was6.83u/g. Compared wort Lipase enzymeactivity in the process of saccharifying, it found that Lipase enzyme activity of wheat maltwithout germ was always lower than that of wheat malt with grem during mashing. Whenremaining the germ of wheat, Lipase enzyme activity in wort declined quite slowly before45min（60℃）during wheat malt mashing, at45min, Lipase deactivation rate was just25.58%;from45min to55min（70℃）, Lipase inactivation was obvious,its rate was89.99%. Whenremoving malt bud,during wheat malt mashing Lipase enzyme activity in wort declinedsharply, the Lipase had been inactivated in55min.（5） After malting, enzyme activity increased significantly and increment of enzymeactivity was between265.44%and346.54%. Different malt library value resulted in big gapof Lipase enzyme activity,Lipase enzyme activity increased with the increase of library value,enzyme activity reached to the maximum value of7.52u/g at40.1%. Enzyme activitydecreased between40.1%and43.06%, Lipase enzyme activity increasing with the increase oflibrary value showed a tendency of normal distribution. When beginning with different maltmushing temperature, Lipase enzyme activity varied differently in converted mush, it foundthat Lipase inavtivation rate was17.49%at45℃for30min, enzyme activity was0.07u/mLand inavtivation rate was91.16%when to70℃, Lipase had been inactivated at70℃for2min; incubating30min at50℃, it could be found that Lipase inavtivation rate was just7.95%,enzyme activity was0.00u/mL and inavtivation rate was100.00%when to65℃; startingmushing at55℃had very serious impact on Lipase and enzyme activity loss was very serious,enzyme activity was0.00u/mL and inavtivation rate was100.00%when to70℃.（6） With different initial mushing temperature conditon, trans-2-nonenal force of wortwas different. Compared35℃with40℃, there was not obvious difference,40℃,45℃and55℃were the same situation, trans-2-nonenal force was the largest of2.18ug/L at50℃, and it was visible different from other conditions.