小麦芽水溶性阿拉伯木聚糖分子结构特征及其在啤酒界面扩张特性中的作用机理

Water-extractable arabinoxylans (WEAXs) in wheat malts have an important impact on beer properties. In this proposal, the effect of Kolbach Index on the contents and molecular structural features of wheat malt WEAXs that are derived from different wheat varieties (Triticum aestivum L.) will be studied. Molecular structural feature of WEAXs includes degree of polymerization of xylose residues in main backbone, degree of arabinose to xylose, an xylose residue of main backbone carrying single or double arabinose residues, and substitution of ferulic acid on arabinose residues. The differences of molecular structure characteristics between WEAXs in beer and in the wheat malt will be compared. And the distribution of the WEAX components on beer foam and in the beer liquor will be determined. The origin of WEAX components could be traced to wheat WEAXs or water-unextractable arabinoxylans by analyzing their molecular structure characteristics, meanwhile their contribution on beer interfacial dilation properties will be compared. Foam property is a significant sensory index of beer quality, which includes size and density of foam, foam retention time, foaming ability, degree of foam dilation, and foam conformation. Impacts of WEAXs contents and their molecular structure characteristics on beer foam properties, surface tension and dilation modulus will be explored. By combining spectropolarimeter and atomic force microscopy, space conformational changes of WEAXs and that under reduced degree of polymerization, desubstituted arabinose and ferulic acid residues, as well as interactions with beer total foam protein, foam hydrophilic protein and hydrophobic protein will be investigated, from which the mechanisms of reaction between wheat malt WEAXs, beer foam proteins and reacted key group are speculated.

小麦芽水溶性阿拉伯木聚糖（WEAXs）对啤酒品质特征具有重要影响。本项目主要研究库值对不同品种小麦芽WEAXs含量与分子结构特征（Dp值、A/X值、主链单个木糖残基上阿拉伯糖单取代或双取代，阿拉伯糖残基上阿魏酸酰基化程度）的影响。对比进入啤酒前后小麦芽WEAXs分子结构特征的差异性，确定小麦芽WEAXs组分在啤酒泡沫与酒液中的分布，根据WEAXs分子结构特征进行溯源（来自小麦WEAXs或水不溶性阿拉伯木聚糖），比较两者对啤酒界面扩张特性贡献的权重。研究WEAXs含量与分子结构特征对啤酒泡沫性质（泡沫大小、密度、泡持时间、起泡力、泡沫膨胀率、泡沫构象）、表面张力、扩张模量等界面扩张特性的作用。结合旋光分光计与原子力显微镜研究WEAXs聚合度降低、脱阿拉伯糖、脱阿魏酰基前后的空间构象及其与啤酒泡沫总蛋白、泡沫亲水蛋白、泡沫疏水蛋白间的作用，推测WEAXs与啤酒泡沫蛋白可能的作用机理与关键基团。

小麦芽含WEAX 0.90% ~ 1.32%，A/X值0.54 ~ 0.56，avDP值14.6 ~ 15.7。WEAX含量增加主要发生于发芽第1 ~ 2天，制麦过程WEAX含量增加91.9% ~ 199.4%，A/X降低7.6% ~ 27.4%，avDP降低77.5% ~ 81.5%。小麦芽适宜库值37.6% ~ 42.7%，芽库值增加有利于提高小麦芽β-(1,4)-内木聚糖酶、β-D-木糖苷酶活性。avDP值随库值增加降低（r = -0.857，p < 0.05），但不影响WEAX含量与A/X值。WEAX的Wamw影响小麦芽粘度（r = 0.821，p < 0.05）。库值38%以上更利于WEAX的降解。.小麦芽WEAX的溶出降解主要集中于糖化过程，WEAX含量增加30.4 % ~ 96.3%、avDP降低63.2% ~ 73.9%、A/X保持不变，组分0.4-12.5 kDa约占86.56 % ~ 92.82 %，发酵后贮变化不显著。啤酒泡沫具有富集糖能力，泡沫中WEAX比除沫啤酒中高35.71%。.小麦芽水溶性蛋白质总量增加181.8 %，各蛋白组分含量与小麦芽粘度负相关、与小麦芽浸出物正相关（p < 0.05）。麦汁制备过程中蛋白质总量增加20.58%，组分1.1-7.6 kDa增加51.96%、>32.1kDa增加15.79%，组分13.2-32.1 kDa减少15.21%。发酵液中蛋白主要为2.1-7.6 kDa组分，占41.71% ~ 49.33%。蛋白组分减少主要发生于主发酵前两天。发酵后贮结束蛋白总量降低18.04%，2.1-7.6 kDa组分相对稳定。.WB、DB、BF中蛋白质Wamw接近，且比大麦啤酒相应部分高。小麦啤酒蛋白13.2-32.1 kDa组分高于大麦啤酒，>32.1kDa组分比大麦啤酒高约5倍。因此浑浊小麦啤酒中含有更多大高分子蛋白，且> 13.2 kDa组分可能是小麦源关键蛋白。.1:1 ~ 1:4分级醇沉纯化WB、DB、BF各组分Wamw差异显著，易于进一步纯化。WEAX组分分布于各个沉淀组分中。AG主要存在于1:2纯化组分中，所占比例略低于WEAX。1:3 ~ 1:4纯化组分中，DG占比例最高，WEAX居第二，Wamw在5163Da以下。啤酒泡沫中MP比除沫啤酒大幅提高，用1:1乙醇可将绝大部分MP分出。