Changes Of Arabinoxylan During Brewing

Arabinoxylan (AX), the main non-starch polysaccharide (NSP) consisting of wheat cell walls, has the characteristics of high viscosity and water-holding ability. AX in wheat malt tends to cause high viscosity and turbidity of wort and beer. Nevertheless, AX also enhances the foam-stability, mellowness and antioxidation of beer. Researches of AX during malting, mashing and fermentation process will improve the quality of wheat malt and beer. In this experiment, four types of wheat (Yannong24, Lumai21, Yan2415, Yan5158) and one type of barley (Baudin) were used as test materials for malting, mashing and brewing tests were carred out. The differences in water-extractable arabinoxylan (WEAX) content, structure and molecular weight (Mw) of malts, as well as their raw materials were compared. The correlations among kolbach index (KI), the WEAX content, structure and Mw of wheat malt were studied. The influences of the addition of wheat malt on the qualities of brewing materials and beer by the tests of mashing and brewing, the changes of WEAX content, structure and Mw during fermentation process of beer were explored. The changes of WEAX during brewing were confirmed. The main conclusions were listed as following:(1) AX in malts and malting materials①Total AX content of wheat was5.48%～6.22%, Arabinose/Xylose (A/X) was0.67～0.69, WEAX content was0.36%～0.47%, A/X was0.62～0.70, average degree of polymerization (avDP) was69.9～80.7. Total AX content of barley was5.91%, A/X was0.52, WEAX content was0.24%, A/X was0.75, avDP was40.7. The contents of water-extractable arabinose (Ara), xylose (Xyl), galactose (Gal) in wheat were higher than barley, but mannose (Man), glucose (Glc) contents were lower.②Total AX content of wheat malt was6.00%～7.17%, A/X was0.58～0.66, WEAX content was0.90%～1.32%, A/X was0.54～0.56, avDP was14.6～15.7. Total AX content of barley malt was6.78%, A/X was0.50, WEAX content was0.51%, A/X was0.55, avDP was9.0. The contents of WEAX, water-extractable Ara, Xyl, Gal and Glc in wheat malts were higher than barley malts, Man content was similar.③The content of WEAX in wheat malt-based wort was119.8～172.0mg/100mL, A/X was0.47～0.51, avDP was3.4～5.1. The content of WEAX in barley malt-based wort was85.9mg/100mL, A/X was0.58, avDP was3.3. The contents of Ara, Xyl, Gal in wheat malt-based wort were higher than barley malt. ④Mw of WEAX in malts was distributed in the range of26930～39620Da, the WEAX of15310-24940Da accounted for50.0%～65.0%of malt WEAX and the WEAX of2780～3070Da accounted for12.8%～42.0%. Mw of WEAX in wort was distributed in the range of4150～8860Da.The WEAX of3010-3820Da accounted for49.5%～76.2%发of wort WEAX and the WEAX of384～415Da accounted for13.9%～46.6%.(2) Correlation between KI and WEAX in wheat malts①When KI increased from32%to42%, the avDP of WEAX in wheat malts was reduced from26.7to13.3, the avDP of WEAX in wheat malt-based wort was reduced from7.1to4.1. WEAX content of wheat malt was1.08%～1.16%, A/X was0.53～0.56, WEAX content in wheat malt-based wort was137.5～140.5mg/100mL, A/X were0.48～0.50. Mashing process promoted high Mw fraction of malt WEAX (>16700Da) degradating to low Mw fraction (<16700Da) in wort. Viscosity was mainly affected by the malt WEAX fraction of22940-29600Da (r=0.821, p<0.05). KI did not affect wort viscosity and the Mw of WEAX in wheat malts.(3) Effects of wheat malt addition on the qualities of mixed malts and beer①WEAX content, avDP and A/X of WEAX in mixed malts had a linear relation with the wheat malt addition. Mw of WEAX in mixed malts was in the range of28190～32920Da, the proportion of WEAX of3300～20000Da was the highest accounting for56.0%～58.0%.②WEAX content, avDP of WEAX in mixed malt-based wort also had a linear relation with the addition of wheat malt. A/X were stable in the range of0.49～0.56. Mw of WEAX in mixed malt-based wort was increased with the addition of wheat malt, the WEAX of1580～1700Da was decreased but the WEAX of22510-17560Da was increased.③Adding wheat malt mainly affected total nitrogen (r=0.968, p<0.01), viscosity (r=0.945,p<0.05) and α-AN (r=-0.990, p<0.01) of final wort, and increase of4-VG content and organic acids in beer, such as oxalic acid, tartaric acid and a-ketone glutaric acid. With the increase of wheat malt, dimethyl sulphide (DMS), free amino nitrogen (a-AN), turbidity, total acidity, polyphenol of beer were decreased, total nitrogen, chromaticity, viscosity,β-glucan and esters contents were increased. The change of viscosity mainly happened in the low-temperayuer storage of beer. When the wheat malt ratio was50%, wheat beer had the best sensory evaluation.(4) Changes of WEAX during brewing①WEAX content in final wort was40.2～65.1mg/100mL, avDP was2.1～2.9, A/X was0.46～0.53. After the primary fermentation process, WEAX content in fermentation broth was41.2～65.6mg/100mL, avDP was2.0～3.0, A/X was0.45～0.51. After secondary fermentation process, WEAX content in fermentation broth was40.0～68.2mg/100mL, avDP was2.1～2.7, A/X was0.38～0.50. WEAX content in beer was40.4～63.5mg/100mL, avDP was2.2～3.0, A/X was0.42～0.53.②More than90%WEAX in final wort was distributed in the range of500～4000Da. After primary fermentation process, the WEAX below500Da was decreased, but the WEAX above4000Da was increased. More than85%WEAX in fermentation broth and beer was distributed in the range of600～4000Da.③During malting, the content of WEAX was increased91.9%～199.4%, A/X was decreased7.6%～27.4%, avDP was decreased77.5%～81.5%. During mashing, WEAX content was increased30.4%～96.3%, A/X was decreased0～13.8%, avDP was decreased63.2%～73.9%. Water-extractable Ara, Xyl, Man and Glc increased during malting and mashing. The contents of WEAX, Ara, Xyl and Gal had no significant differences in final wort, fermentation broth and beer. Man and Glc decreased and then had no significant changes after primary fermentation process. A/X of WEAX in beer increased after adding wheat malt, but had no significant changes during primary fermentation process. avDP was in the range of2～3during the fermentation processes. Mw of WEAX was decreased3～7times during mashing, but it was tended toward the stability after the primary fermentation process.