Abstract
This study presents the results of conventional aqueous (CE) and non-conventional ultrasound-assisted (UAE) extractions of polyphenolic compounds from lees extracts of red wine varieties (Merlot and Vranac). The effect of ultrasound extraction time (t, s), and amplitude (A,%) from a 400 W ultrasound processor with different ultrasonic probes diameters (Ds, mm) on the amount and profile of polyphenolic compounds in the obtained extracts was investigated and compared to CE. The optimal conditions resulting in maximum extraction of phenolic compounds were: Probe diameter of 22 mm, amplitude 90% and extraction time for Vranac wine lees 1500 s and for Merlot wine lees extraction time of 1361 s. UAE proved to be significantly more effective in enhancing the extraction capacity of trans-resveratrol glucoside (30.57% to 300%), trans-resveratrol (36.36% to 45.75%), quercetin (39.94% to 43.83%), kaempferol (65.13% to 72.73%), petunidin-3-glucoside (41.53% to 64.95%), malvidin-3-glucoside (47.63% to 89.17%), malvidin-3-(6-O-acetyl) glucoside (23.84% to 49.74%), and malvidin-3-(6-O-p-coumaroyl) glucoside (26.77% to 34.93%) as compared to CE. Ultrasound reduced the extraction time (2.5-fold) and showed an increase of antioxidant potential by 76.39% (DPPH) and 125.83% (FRAP) compared to CE.
Highlights
Grapes are one of the fruit crops produced in largest quantities throughout the world
Besides the detailed analysis of conditions for UAE of the compounds trans-resveratrol glucoside, trans-resveratrol, quercetin, kaempferol, petunidin-3-glucoside, malvidin-3-glucoside, malvidin-3-(6-O-acetyl) glucoside and malvidin-3-(6-O-p-coumaroyl) glucoside, which prevail in the wine lees and have high individual antioxidant potential (AOP), we further discovered the presence of other phenolic compounds that contribute to the overall AOP, but are primarily responsible for the astringent taste of red wines
Of polyphenols from lees of the Merlot variety results in significantly higher yields of bioactive compounds in the extracts compared to conventional extraction (CE)
Summary
Grapes are one of the fruit crops produced in largest quantities throughout the world. The annual production of 60 million tons of grapes is mostly for wine production, which generates huge amounts of by-products such as stalks, pomace, seeds, and lees. These by-products are potentially good sources of valuable bioactive compounds. Wine lees are the sediment remaining in vessels containing wine after fermentation and during wine maturation [2]. It is a known fact that the skin and seeds of black grape berries (V. vinifera L.), as well as red wines naturally contain more than 200 different polyphenolic compounds [4,5,6,7,8,9]. Previous studies performed on extraction of polyphenolic compounds from red grapes were mostly focused on their extraction from seeds or the epidermis of grape berries
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