The Australian Wine Research Institute, P.O. Box 197, Glen Osmond, Adelaide, SA 5064, Australia.
J Agric Food Chem. 2011 Mar 23;59(6):2652-62. doi: 10.1021/jf104334v. Epub 2011 Mar 1.
Consumers expect white wines to be clear. During the storage of wines, grape proteins can aggregate to form haze. These proteins, particularly chitinases and thaumatin-like proteins (TL-proteins), need to be removed, and this is done through adsorption by bentonite, an effective but inefficient wine-processing step. Alternative processes are sought, but, for them to be successful, an in-depth understanding of the causes of protein hazing is required. This study investigated the role played by ionic strength (I) and sulfate toward the aggregation of TL-proteins and chitinases upon heating. Purified proteins were dissolved in model wine and analyzed by dynamic light scattering (DLS). The effect of I on protein aggregation was investigated within the range from 2 to 500 mM/L. For chitinases, aggregation occurred during heating with I values of 100 and 500 mM/L, depending on the isoform. This aggregation immediately led to the formation of large particles (3 μm, visible haze after cooling). TL-protein aggregation was observed only with I of 500 mM/L; it mainly developed during cooling and led to the formation of finite aggregates (400 nm) that remained invisible. With sulfate in the medium chitinases formed visible haze immediately when heat was applied, whereas TL-proteins aggregated during cooling but not into particles large enough to be visible to the naked eye. The data show that the aggregation mechanisms of TL-proteins and chitinases are different and are influenced by the ionic strength and ionic content of the model wine. Under the conditions used in this study, chitinases were more prone to precipitate and form haze than TL-proteins.
消费者期望白葡萄酒是清澈的。在葡萄酒储存过程中，葡萄蛋白可能会聚集形成浑浊。这些蛋白质，特别是几丁质酶和类硫素蛋白（TL-蛋白），需要被去除，而这是通过膨润土的吸附来实现的，这是一种有效但效率不高的葡萄酒处理步骤。人们正在寻找替代工艺，但要成功实施这些工艺，就需要深入了解导致蛋白质浑浊的原因。本研究调查了离子强度（I）和硫酸盐对 TL-蛋白和几丁质酶在加热时聚集的作用。将纯化的蛋白质溶解在模型葡萄酒中，并通过动态光散射（DLS）进行分析。在 2 至 500mM/L 的范围内研究了 I 对蛋白质聚集的影响。对于几丁质酶，在 100 和 500mM/L 的 I 值下，在加热时发生聚集，这取决于同工型。这种聚集立即导致形成大颗粒（3μm，冷却后可见浑浊）。仅在 I 为 500mM/L 时观察到 TL-蛋白聚集；它主要在冷却过程中发展，并导致形成有限的聚集体（400nm），这些聚集体仍然不可见。在介质中有硫酸盐的情况下，几丁质酶在加热时立即形成可见的浑浊，而 TL-蛋白在冷却时聚集，但聚集到肉眼可见的大颗粒的程度不足以形成浑浊。数据表明，TL-蛋白和几丁质酶的聚集机制不同，受模型葡萄酒的离子强度和离子含量的影响。在本研究中使用的条件下，几丁质酶比 TL-蛋白更容易沉淀并形成浑浊。
