engleski

THE POTENTIAL OF GRAPE STEMS ETHANOLIC EXTRACTS FOR LIQUEUR PRODUCTION

The wine industry produces large amounts of byproducts, which represents a waste management issue both ecologically and economically. Among all the byproducts, grape stems, which constitute up to 25 % of total byproducts are discarded before winemaking process and are the less characterised and valorised material. Nowadays, grape stems potential for the production of spirits, dietary fiber, ruminants feed and plant protein concentrates is being investigated. As well as other grape byproducts, grape stems have been described as a natural source of biologically active compounds. This byproduct may be useful as a source of potentially functional ingredients providing the opportunity of developing innovative added value products, e.g. liqueurs. Herbal liqueurs are alcoholic beverages produced by the maceration of plants in hydro-alcoholic base and are highly valued for their medicinal properties. Medicinal properties of herbal liqueurs are attributed to biologically active compounds, e.g. polyphenolic compounds. However, the potential application of grape stems for liqueuer base production requires the optimization of its maceration conditions in order to extract polyphenolics as much as possible accompanied with desirable colour. In the present study, ethanolic extracts from grape stems were prepared by the maceration of grape stems in hydro-alcoholic base (45 %, 70 % and 96 % v/v of ethanol). Extracts were evaluated for total polyphenolic content (TPC), polyphenolic profile (HPLC) and antioxidant activity (FRAP and DPPH) after 24 hours, 1, 2 and 3 months of maceration. Additionally, chromatic characteristics of extracts were determined. The characteristic colour of extracts ranges from greenish yellow after 24 h of maceration to brown at the end of maceration. Both the polyphenolic content and antioxidant activity reach the highest values after 3 months of maceration. The highest TPC and antioxidant activity were observed in the extracts produced with 70 % of ethanol. The main goups of polyphenols were flavonoids, stilbenes and phenolic acids. Based on high content of bioactive compounds and valuable antioxidant activity, grape stems might be useful as a source of potentially functional ingredients in the elaboration of innovative liqueurs.

antioxidant activity ; grape stems ; liqueur ; maceration ; polyphenols

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