Comparison of different extraction solvents and sonication times for characterization of antioxidant activity and polyphenol composition in mulberry (Morus alba L.)

Various extraction solvents and sonication treatment times were compared to determine antioxidant activity and polyphenol composition in mulberry ( Morus alba L.) fruits of the Gwasang No. 2 variety. Mulberry fruits were extracted with ethanol, methanol, acidic methanol (0.1% HCl), or acidic ethanol (0.1% HCl) with 0–60-min sonication to measure total phenolic content and antioxidant activity (DPPH radical scavenging activity). Moreover, a high-performance liquid chromatography method to analyze polyphenol compositions in mulberry extracts was developed and levels of common polyphenolic compounds in the different extracts were determined. The effects of different methanol ratios in acidic aqueous methanol (0–100%) on individual polyphenol contents in the extracts after 30 min of sonication were investigated. The total phenolic contents of the extracts using acidic methanol and sonicated for 60 min were significantly higher than phenolic contents upon extraction with other solvents and sonication times ( p < 0.001). Interestingly, antioxidant activity of the extracts using acidic ethanol sonicated for 60 min was significantly higher than that of other extracts ( p < 0.001). Cyanidin-3-glucoside and 3-rutinoside were the major polyphenol compounds in all mulberry extracts. Cyanidin-3-glucoside and 3-rutinoside concentrations were highest in the acidic methanol extract sonicated for 30 min (15,664 and 19,630 μg/g DW) ( p < 0.001). The acidic methanol extract sonicated for 30 min contained significantly higher polyphenolic compound content than that of other extracts ( p < 0.001). A decreased methanol ratio (0–80%) in acidic aqueous methanol resulted in chlorogenic acid overestimation in mulberry extracts. Thus, acidic 100% methanol with 30-min sonication is recommended for polyphenol analysis in mulberry.