Relationship Between Kolbach Index And Quality Of Wheat Malt

Wheat malt which was used as good raw material and price lever in beer brewing, is theguarantee for the fast development of China’s beer industry in the long run. One of thehighlighted technology problems in wheat malt beer brewing is that the protein content ishigh in wheat. Kolbach indices that is the ratio of the percentage of soluble nitrogen in thetotal nitrogen, is an important index that reflect wheat malt dissolve degree and wheat maltquality evaluation. Wheat (Triticum aestivum L) malts with different Kolbach indices(31.4%~45.5%) from the same wheat variety named L-2were prepared by controlling steepout moisture and germination time. The protein fractions, the starch components, non-starchpolysaccharides and degradative enzyme activities of the wheat malts was analysed toexplore the rules of the endosperm components degradation. The main conclusions were asfollowings:(1) The relationship between Kolbach index and quality indices of wheat maltsKolbach index had positive correlation with extract and α-AN (P<0.05); had negativecorrelation with saccharifying power and pH value (P<0.05); and had significant positivecorrelation with chromaticity, acidity and malting loss (P<0.05). The saccharifying powerand α-AN content were comparatively higher at the Kolbach index of39.5%, while thesaccharifying power was496.72WK and α-AN content was166.03mg/100mg.(2) The relationship between Kolbach index and protein components degradation ofwheat malts①When Kolbach index were in the range of31.4%~45.5%, the ALSP of the maltswere increased91.18%~216.40%; the globulins were increased62.73%~140.91%; thegliadins were decreased37.85%~79.92%; the glutenins were decreased23.32%~57.34%.The Kolbach index had significant positive correlation with the ALSP increased ratio and theglutenins decreased ratio (P<0.01); and it had positive correlation with globulins increasedratio and gliadins decreased ratio (P<0.01). In wheat malting process, the degradation ofgliadins give priority to glutenins degradation; the increase of ALSP was given priority tothe increase of globulins. When in the range of31.4%to45.5%, with the increase of theKolbach index the protein degradation process of wheat malt was linear intensified.②The molecular weight of the ALSP in wheat were in the range of15.4~72.3kDa,after malting the protein which molecular weight was84.4and43.8kDa were produced, theprotein which molecular weight were in the range of21.0~64.3kDa were decomposed, and the protein which molecular weight was60.1and15.4kDa were correspondingly increased95.44%~129.64%,62.70%~257.95%.③The molecular weight of the globulins in wheat were in the range of14.9~70.8kDa,after malting the protein which molecular weight were in the range of52.3~70.8kDa weredecomposed，and the content of the protein which molecular weight were in the range of14.9~35.0kDa were increased.④The molecular weights of the gliadins in wheat were in the range of17.6~60.0kDa,the content of the protein with the molecular weight was31.6~35.2kDa were58.69%of thecontent of all the gliadins content. After malting the protein which molecular weight were inthe range of17.6~60.0kDa were decomposed, and the main molecular weights of thegliadins in wheat malts were35.2、31.6and17.6kDa.⑤The molecular weights of the glutenins in wheat were in the range of34.3~108.5kDa,after malting all the protein were decomposed, especially the protein with the molecularweight of83.2and63.8kDa were almost disappear in wheat malts.⑥With the increase of Kolbach index, the content of60.0kDa gliadins,101.5kDa,75.6kDa glutenins;64.3kDa ALSP were significant decreased. And17.6kDa globulin wassignificant highly increased.⑦After saccharified the content of protein with the molecular weight of10.6~15.4kDawere increased. The content of the13.5kDa and11.3kDa protein in standard wort hadpositive correlation with viscosity （P<0.05）; The content of the10.6kDa protein hassignificant positive correlation with the chromaticity (P<0.01).⑧The hydrophobicity of the standard wort had significant negative correlation withKolbach index (P<0.01); and had significant positive correlation with the protein with themolecular weight was36.8kDa (P<0.05).(3) The relationship between Kolbach index and polysaccharides componentsdegradation of wheat malts①When Kolbach index were in the range of31.4%~39.5%, the degradation of theamylase, amylopectin was severe, but when Kolbach index were in the range of39.5%~45.5%, the amylase, amylopectin and Ape/Amy had no significant difference among thewheat malts. ②After malting the soluble β-glucan content of wheat malts was decreased. Thecontent of WEAXs was increased. When the Kolbach index was less than39.5%, the contentof WEAXs had positive correlation with viscosity.(4) The relationship between Kolbach index and sugars content of standard wortWort concentration of the standard wort was in the range of8.47%~8.66%, and theextract was in the range of81.29%~82.71%, and the two quality indices had no differenceamong the different wheat malts with different Kolbach index. The chromaticity had positivecorrelations with the glucose and mannose (P<0.05); viscosity had significant positivecorrelations with WEAXs content of standard wort (P<0.01). The Kolbach index hadsignificant positive correlateions with glucose (P<0.01) and had negative correlateions withWEAXs (P<0.05).(5) The relationship between Kolbach index and the degradative enzyme activities①After malted the a-amylase, β-amylase, protease, β-glucanase, β-D-xylosidase, β-(1,4)-endoxylanase activity of the malts was increased compared with which of the wheat. Andthe a-amylase, protease, β-glucanase, β-D-xylosidase, β-(1,4)-endoxylanase activity amongthe malts with different Kolbach index were significant different. There were exist positivecorrelations among the a-amylase, β-amylase, β-glucanase, β-D-xylosidase, β-(1,4)-endoxylanase activity of wheat malts (P<0.05).②When the Kolbach index was less than37.0%, all the degradative enzyme activitieswas increased, when the Kolbach index were37.6%,39.5%and42.7%, the β-glucanase, β-D-xylosidase and protease reached to the peak value, correspondingly; So to acquire highestdegradative enzyme activities the suitable Kolbach index was in the range of37.6%~42.7%.(6) The key factor which affect the malt quality and the suitable Kolbach index ofwheat maltsThe key factor that affected the hydrophobicity of the wort was36.8kDa pritein；Thekey factors that affected the viscosity were13.5and11.5kDaproein and WEAXs. The keyfactors that affected the chromaticity were α-AN,10.6kDa protein, glucose and mannose. Itwas when the Kolbach index was in the range of37.6%~42.7%that the wheat malts qualitywas the best.