Abstract
The use of grape stems for the extraction of bioactive compounds to be used in the pharmaceutical, food, and cosmetic industries is a promising objective. The aim of this work is to determine the influence of the different extraction conditions (temperature, ethanol concentration, and ratio of sample/solvent) on phenolic composition and antioxidant capacity of Mazuelo stem extracts. In general, the ethanol concentration of the extraction solvent was the factor that had the greatest influence on the extraction of different bioactive compounds. The greatest content of total phenolic compounds and the highest antioxidant activity of the extracts were obtained with 50% ethanol and at 40 °C. The most abundant compound found in the different extracts obtained from Mazuelo grape stem was (+)-catechin, but appreciable concentrations of gallic acid, a quercetin derivative, and stilbenes (trans-resveratrol and trans-ε-viniferin) were also extracted. Quercetin and malvidin-3-glucoside showed the highest correlation with the antioxidant capacity of the extracts, while stilbenes did not present such relation. The maximum concentration of gallic acid was extracted with water but the extraction of most of the compounds was maximum on using 50% ethanol. Consequently, the selection of the extraction method to be used will depend on the particular compound to be extracted in greatest quantity.
Highlights
According to figures from the International Organization of Vine and Wine (OIV), grape production in 2016 reached a total of 28,233,181 tons in Europe and, this sector has an important economic impact for many European countries
We investigated the influence of ethanol concentration, solid/solvent ratio, and temperature on the extraction of bioactive compounds from grape stems
Only gallic acid was included (GA), as it was the only compound extracted significantly when water was used as extraction solvent
Summary
According to figures from the International Organization of Vine and Wine (OIV), grape production in 2016 reached a total of 28,233,181 tons in Europe and, this sector has an important economic impact for many European countries. From this large grape production, approximately 75% is used for the winemaking [1]. Grape stems are discarded during the destemming stage as their presence during vinification would introduce green tannins in the wine, as well as give undesirable herbaceous and vegetable aromas.
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