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Efficiency of stilbene extraction- comparison of the conventional and ultrasonic assisted extraction

Polyphenols are large family of natural antioxidants, bioactive compounds widely distributed in plants. They have been studied for several decades because of their potentially beneficial properties for human health. In recent times great interest is devoted to subclass of stilbenes, especially resveratrol and its derivatives. In this study, we analyzed the influence of different extraction methods on the efficiency of stilbene extraction. Commercially available sage leaves (20 g), dried and powdered, were extracted with 100 mL of alcoholic solvent (ethanol/water, 80:20 v/v). The extracts were prepared in four ways: CE (conventional solvent extraction, 60˚ C, 60 min) ; CE-M (CE followed with maceration at RT for 48 h) ; CE-US-M (CE followed with additional ultrasonication for 10 min, and maceration at RT for 48 h) ; US-M (ultrasonication for 30 minutes followed with 48 h maceration at RT). Total phenols, flavonoids, nonflavonoids and flavans were determined using spectrophotometric methods. The content of resveratrol and its derivatives was analyzed by HPLC-RP-DAD. Antioxidant activity of extracts was determined as free radical scavenging ability (DPPH) and ferric reducing/antioxidant power (FRAP). According to the obtained results all extracts were rich in phenolic compounds and had good antioxidant properties. The extended maceration time (CE-M vs. CE) resulted in an improved extraction of total phenols, flavonoids, nonflavonoids and flavans but not of stilbenes. Research results confirmed that combination of conventional extraction and ultrasonic assisted extraction have changed polyphenolic profile of extracts, although significant differences in the share of resveratrol monomers between CE, CE-US-M and US-M were not confirmed. The average amount of resveratrol monomers (cis + trans) in CE, CE-US-M and US-M was 99.99± ; ; 3.198 mg/L of extract. CE-US-M resulted with higher amounts of resveratrol derivatives indicating the positive impact of ultrasonication on the efficiency of the extraction of stilbenes. Particularly good results were obtained with US-M. Although US-M extract was not rich in total phenols, it contained 2-fold higher amounts of resveratrol derivatives compared to CE and CE-US-M extracts. Stilbenes extraction efficiency research is important for getting extracts with good antioxidant properties and rich in these natural bioactive compounds. Such extracts can be used in the production of functional food or dietary supplements.

polyphenols; stilbenes; HPLC; ultrasonic assisted extraction

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