Physicochemical characterization of Vranec wines using fournier transform infrared (FT-IR) spectroscopy

In this study, Vranec wines from Tikveš wine district were produced (vintage 2022) and analyzed with fournier transform infrared (FT-IR) spectroscopy. The basic physicochemical parameters have been determined: alcohol, density, reducing sugars, pH, total acidity, volatile acidity, free and total SO2. All wines presented good quality, containing relatively high content of alcohol (range: 12.5 to 15.98%). The pH ranged from 3.53 to 3.74, the total acidity was in range from 4.63 to 7.74 g/L and the volatile acidity ranged from 0.34 to 0.78 g/L, which means that all wines were chemically and microbiologically stable. In addition, all wines were protected from oxidation, containing sufficient free SO2 (on average: 9.28 mg/L) and total SO2 (on average: 21.07 mg/L). The content of individual organic acids were also determined, in which tartaric acid was the dominant compound (average value: 2.92 g/L), followed by malic acid (average value: 0.69 g/L), lactic acid (average value: 0.52 g/L) and citric acid (average value: 0.31 g/L). Gluconic acid, which is the most important parameter for the health of grapes since it is considered as indicator of Botrytis cinerea disease, was determined for the first time in Macedonian Vranec wines, and the content ranged from 0.86 to 3.80 g/L, which are considered as normal values, confirming the physical and chemical stability of wines. In addition, the Folin-Ciocalteau (FC) Index and colour parameters have been determined. All wines presented relatively high FC index, as expected, since Vranec variety is rich in polyphenols. The red colour dominated (range: 51.44 to 55.17%), followed by yellow colour (range: 32.96 to 34.06%) and blue colour (range: 11.8 to 14.51%). All wines presented satisfactory brilliance, ranged in 52.79 to 59.38%. In general, Vranec wines presented very good physical, chemical and microbiological stability, characteristic for high quality red wines.

Keywords: basic parameters, organic acids, colour parameters, Vranec, FT-IR.