Scientific study of 13C/12C carbon and 18O/16O oxygen stable isotopes biological fractionation in grapes in the Black Sea, Don Basin and the Western Caspian regions

The report presents the results of a study of carbon and oxygen stable isotopes in carbohydrates and intracellular water of red and white grapes of 2016 wine-growing season in the Crimean peninsula areas, South-west coast of the Greater Caucasus, the Don basin and the Western Caspian region. The mass concentration of reducing sugars in the studied grape samples has been from 17.5 to 25.0 g/100 ml, titrated acids concentration (based on tartaric acid) – from 6.0 to 9.1 g/l, the buffer capacity 34.1–63.2 mg-Eq/l. Red and white wine made from respective grapes contained from 0.5 to 3.6 g/l of residual sugar; from 11.1 to 14.5% ethanol by volume; buffer capacity was 35.2–52.6 mg-Eq/l. It has been found that the δ13CVPDB values for carbohydrates of red and white grape varieties as a result of biological fractionation of carbon isotopes in the agro-climatic conditions of plant growth for the studied geographical areas are ranging from − 26.74 to − 20.74‰ (the Crimean peninsula); from − 27.31 to − 21.58‰ (South West Coast of the Greater Caucasus), from − 27.33 to − 24.73‰ (Don Basin) and from − 26.64 to − 23.17‰ (West Caspian). The δ13CVPDB values for ethanol of the red and white dry wines range from − 28.52 to − 24.26‰ (the Crimean peninsula); from − 29.23 to − 24.52‰ (South West Coast of the Greater Caucasus); from − 28.97 to − 26.22‰ (Don Basin); from − 29.14 to − 25.22‰ (Western Caspian). Compared with the surface water and groundwater (averages from δ18OVSMOW− 13.90 to − 6.38‰) and with precipitation (averages from δ18OVSMOW − 10.30 to − 9.04‰) the δ18OVSMOW values in intracellular water of grapes are the following: for the Crimean peninsula grapes, from 0.40 to 4.97‰; the South West Coast of the Greater Caucasus, from -2.11 to 6.29‰; the Don Basin, from − 2.21 to 6.26‰; the Western Caspian, from − 0.24 to 1.44‰. It has been noted that in conditions of water shortage caused by low rainfall or lack of rainfall and irrigation, grapes are prone to the accumulation of “heavy” 13C carbon isotope due to changes in isotopic exchange with the environment through a partial reduction in the intensity of transpiration and photosynthesis.