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In Situ Determination of Fructose Isomer Concentrations in Wine Using 13C Quantitative Nuclear Magnetic Resonance Spectroscopy

Colombo, Cinzia, Aupic, Clara, Lewis, Andrew R., Pinto, B. Mario
Journal of agricultural and food chemistry 2015 v.63 no.38 pp. 8551-8559
bottling, ethanol, fermentation, fructose, grape must, isomers, nuclear magnetic resonance spectroscopy, pH, sweetness, temperature, winemaking, wines
A practical method for simultaneously quantifying fructose and ethanol contents in wines using 13C quantitative nuclear magnetic resonance (qNMR) spectroscopy is reported. Less than 0.6 mL of wine is needed, and the method leaves an unmodified sample available for subsequent testing or additional analyses. The relative ratios of the five known fructose isomers in ethanolic solutions at different pH and their variations with the temperature are also reported. The data are correlated with the sweetness of wines. The technique was applied to commercially available wines, and the results are compared to other methods. Sugar levels above 0.6 g/L can also be measured. A simple adaptation of the method permits measurement of different carbohydrates using integration of single peaks for each compound, in combination with an external reference 13C qNMR spectrum of a sample with a known concentration. The method can be applied at all stages of wine production, including grape must, during fermentation, and before and after bottling.