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

Abstract

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, Southwest 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 δ 13 C VPDB 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 δ 13 C VPDB 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 δ 18 O VSMOW −13.90 to −6.38) and with precipitation (averages from δ 18 O VSMOW − 10.30 to −9.04) the δ 18 O VSMOW 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" 13 C carbon isotope due to changes in isotopic exchange with the environment through a partial reduction in the intensity of transpiration and photosynthesis.

Mass-spectrometric study on13C/12C carbon and18O/16O oxygen stable isotopes distributions in grapes and wines from the Black Sea regions

“…The results of our study characterizing the fractionation of carbon isotopes in native carbohydrates (sugars) and also oxygen isotopes in intracellular water as well as in wines correlate very well with the results of our studies of 2015-2016 in the Crimean Peninsula [1,2] and the published data of other researches, which were conducted in other geographical regions with similar agroclimatic conditions, frequent water deficiency and an irregular irrigation (or total absence of that) during the vegetative period [10][11][12][13][14][15][16][17][18].…”

“…The main area of study on the South West Coast of the Greater Caucasus was the Anapa district (Semigorye area). Scientific data on the Black Sea areas, including climate, soils and grapes varieties have been reported in the previous publications about results of the studies of 2015-2016 [1,2].…”