Effect of grape variety, place of growth, and processing technology on the physical and chemical indicators of grape pomace

Introduction. Any waste can become a raw material for new products. Therefore, waste should be considered as secondary material resources. Grape pomace is the basic waste of wine industry, and research in its chemical composition may allow for a more effective recycling of food industry waste. Study objects and methods. The research featured sweet and fermented pomace of white and red grapes, namely “Chardonnay”, “Sauvignon Blanc”, “Riesling”, “Pinot Blanc”, “Traminer Pink”, “Viognier”, “Morava” “Pinot Noir”, “Roesler”, “Cabernet Sauvignon”, “Merlot”, “Saperavi”, and “Rebo”. They were obtained in the production of wines at wineries in the Krasnodar region. Mass concentrations of organic acids and cations of alkaline and alkaline-earth elements were determined in extracts by capillary electrophoresis. The data was converted to dry matter. Moisture content was calculated as a percentage of the change in the mass of grape pomace. Results and discussion. The moisture content of sweet pomace varied from 49.33 ± 2.04 to 70.35 ± 0.60%, and in fermented pomace – from 47.49 ± 0.02 to 64.24 ± 0.60%. The varieties were studied for mass concentrations of tartaric, malic, succinic, citric, and lactic acids. Tartaric and malic acids proved to be the most abundant ones. The pomace of Riesling grapes had the greatest amount of tartaric acid (104.47 ± 4.16 g/kg). The “Chardonnay” variety proved rich in malic acid (19.40 ± 2.67 g/kg), while the “Morava” pomace had the biggest amount of citric acid (12.61 ± 1.12) and succinic acid (11.72 ± 1.23). The research also defined concentrations of alkaline and alkaline-earth elements. Their content ranged from 41.04 to 3.29 g/kg. Potassium appeared to be the main cation in the pomace samples. The share of potassium in the total mineralization of pomace was up to 94%. The “Riesling” variety grown near Novorossiysk had the largest amount of potassium (36.46 ± 4.65 g/kg). The samples demonstrated a significant correlation between the content of tartaric acid and potassium. Conclusion. The research revealed a significant variation in the concentration of the organic acids and cations of alkaline and alkalineearth metals, depending on the grape variety, the place of its growth, and processing. The grape pomace samples differed moisture content. It depended on the volume of the liquid fraction, i.e. wort or wine material selected during pressing.