McRae Jacqui M, Kirby Nigel, Mertens Haydyn D T, Kassara Stella, Smith Paul A
The Australian Wine Research Institute , P.O. Box 197, Glen Osmond, South Australia 5064, Australia.
J Agric Food Chem. 2014 Jul 23;62(29):7216-24. doi: 10.1021/jf405308m. Epub 2014 Jul 10.
The molecular size of wine tannins can influence astringency, and yet it has been unclear as to whether the standard methods for determining average tannin molecular weight (MW), including gel-permeation chromatography (GPC) and depolymerization reactions, are actually related to the size of the tannin in wine-like conditions. Small-angle X-ray scattering (SAXS) was therefore used to determine the molecular sizes and corresponding MWs of wine tannin samples from 3 and 7 year old Cabernet Sauvignon wine in a variety of wine-like matrixes: 5-15% and 100% ethanol; 0-200 mM NaCl and pH 3.0-4.0, and compared to those measured using the standard methods. The SAXS results indicated that the tannin samples from the older wine were larger than those of the younger wine and that wine composition did not greatly impact on tannin molecular size. The average tannin MWs as determined by GPC correlated strongly with the SAXS results, suggesting that this method does give a good indication of tannin molecular size in wine-like conditions. The MW as determined from the depolymerization reactions did not correlate as strongly with the SAXS results. To our knowledge, SAXS measurements have not previously been attempted for wine tannins.
葡萄酒中单宁的分子大小会影响涩味，但目前尚不清楚包括凝胶渗透色谱法（GPC）和解聚反应在内的测定平均单宁分子量（MW）的标准方法，在类似葡萄酒的条件下是否真的与单宁的大小相关。因此，采用小角X射线散射（SAXS）来测定来自3年和7年树龄赤霞珠葡萄酒的单宁样品在多种类似葡萄酒基质中的分子大小及相应的分子量，这些基质包括：5%-15%和100%乙醇；0-200 mM氯化钠以及pH值为3.0-4.0，并与使用标准方法测得的结果进行比较。SAXS结果表明，年份较长葡萄酒中的单宁样品比年份较短葡萄酒中的单宁样品更大，且葡萄酒成分对单宁分子大小影响不大。GPC测定的单宁平均分子量与SAXS结果高度相关，这表明该方法确实能很好地指示类似葡萄酒条件下单宁的分子大小。通过解聚反应测定的分子量与SAXS结果的相关性则没那么强。据我们所知，此前尚未尝试过对葡萄酒单宁进行SAXS测量。
