Yanqi Qu, Yuheng Chen, Yue Tian, Ting Wang, and Lili He*
*Department of Food Science, University of Massachusetts, Amherst , Room 344, 102 Holdsworth Way, Amherst, MA 01003 (lilihe@foodsci.umass.edu)
The chemical profile of red wine is considered as an important criteria to assess overall red wine quality. Recently, surface-enhanced Raman spectroscopy (SERS) has emerged as a tool with good potential for wine research. Herein, a comprehensive method was developed to analyze components in red wines via a fabricated, nanoparticle-based mirror SERS substrate. A water-immiscible hybrid solvent was designed to mix with red wine samples and two separated phases were created after dissolution. The aqueous wine phase was tested with mirror substrate and was observed sharing similar Raman spectra with condensed tannins (i.e., a major component of red wine astringency) from grape extract, where signature peaks were further characterized as NADH (i.e., a coenzyme from plant tissues). Therefore, NADH was considered as an indicator to quantify condensed tannins in red wine, because both are released from grape tissues during fermentation and further statistical analysis also confirmed their correlation. In the solvent phase, NADH was eliminated due to high water solubility and interesting components (e.g., condensed tannin, resveratrol, anthocyanins, gallic acid, and SO2) were extracted from red wines. The solvent phase was subsequently incorporated with silver nanoparticles to fabricate the mirror substrate and to concentrate bioactive components to SERS active domains. With the SERS analysis, five interested compounds were successfully identified in the wine extract through spectra matching analysis, which demonstrated the capability of SERS in profiling red wine chemicals. Overall, this study demonstrated a simple method to quantify condensed tannins in red wines and developed a multicomponent approach to assess the quality aspects of red wines in astringency, color, and health benefits.

Funding Support: NEC Laboratories America, Department of Food Science, UMass Amherst