Brussels Photonics (B-PHOT), Department of Applied Physics and Photonics, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium.
Institute of Electronic Structure and Laser (IESL), Foundation for Research and Technology-Hellas (FORTH), 70013 Heraklion, Greece.
Biosensors (Basel). 2022 Apr 9;12(4):227. doi: 10.3390/bios12040227.
Due to its physical, chemical, and structural properties, oakwood is widely used in the production of barrels for wine ageing. When in contact with the wine, oak continuously releases aromatic compounds such as lignin, tannin, and cellulose to the liquid. Due to the release process, oak loses its characteristic aromatic compounds in time; hence, the flavour that it gives to the enclosed wine decreases for repeated wine refills and a barrel replacement is required. Currently, the estimation of the maximum number of refills is empirical and its underestimation or overestimation can impose unnecessary costs and impair the quality of the wine. Therefore, there is a clear need to quantify the presence of the aforementioned aromatic compounds in an oak barrel prior to a refill. This work constitutes a study to examine noninvasive optical biosensing techniques for the characterization of an oak barrel used in wine ageing, towards the development of a model to unveil its lifespan without inducing structural damage. Spectroscopic diagnostic techniques, such as reflectance, fluorescence, and Raman scattering measurements are employed to assess the change in the chemical composition of the oakwood barrel (tannin and lignin presence) and its dependence on repeated refills. To our knowledge, this is the first time that we present a benchmarking study of oak barrel ageing characteristics through spectroscopic methods for the wine industry. The spectroscopic data are processed using standard chemometric techniques, such as Linear Discriminant Analysis and Partial Least Squares Discriminant Analysis. Results of a study of fresh, one-time-used, and two-times-used oak barrel samples demonstrate that reflectance spectroscopy can be a valuable tool for the characterization of oak barrels. Moreover, reflectance spectroscopy has demonstrated the most accurate classification performance. The highest accuracy has been obtained by a Partial Least Squares Discriminant Analysis model that has been able to classify all the oakwood samples from the barrels with >99% accuracy. These preliminary results pave a way for the application of cost-effective and non-invasive biosensing techniques based on reflectance spectroscopy for oak barrels assessment.
由于橡木具有物理、化学和结构特性，因此被广泛用于葡萄酒陈酿的桶生产。当与葡萄酒接触时，橡木会不断向液体中释放芳香化合物，如木质素、单宁和纤维素。由于释放过程，橡木会及时失去其特征性的芳香化合物；因此，重复灌装和更换桶时，橡木赋予葡萄酒的风味会减少。目前，最大灌装次数的估计是经验性的，其低估或高估可能会带来不必要的成本，并损害葡萄酒的质量。因此，在进行灌装之前，需要对橡木桶中上述芳香化合物的存在进行定量分析。这项工作构成了一项研究，旨在检查非侵入性光学生物传感技术在葡萄酒陈酿用橡木桶的特性表征中的应用，以开发一种无需引起结构损坏即可揭示其使用寿命的模型。采用反射率、荧光和拉曼散射测量等光谱诊断技术来评估橡木桶的化学成分变化（单宁和木质素的存在）及其对重复灌装的依赖性。据我们所知，这是首次通过光谱方法对葡萄酒行业中的橡木桶老化特性进行基准研究。使用标准化学计量技术（如线性判别分析和偏最小二乘判别分析）处理光谱数据。对新鲜、一次性使用和两次使用的橡木桶样品的研究结果表明，反射光谱可以成为橡木桶特性表征的有用工具。此外，反射光谱显示出最准确的分类性能。偏最小二乘判别分析模型的分类准确率最高，能够以>99%的准确率对来自所有橡木桶的样品进行分类。这些初步结果为基于反射光谱的具有成本效益的非侵入式生物传感技术在橡木桶评估中的应用铺平了道路。
