Ultrasound-enhanced subcritical water extraction of naphthoquinone pigments from purple gromwell (Lithospermum erythrorhizon) to higher yield and bioactivity

Abstract

Naphthoquinone pigments were extracted from purple gromwell (Lithospermum erythrorhizon) via ultrasoundenhanced subcritical water extraction (USWE). USWE was compared with supercritical CO2 fluid extraction (SCE) and Soxhlet extraction (SE) on the extraction yield of naphthoquinone pigments and the components and various activities of the extracts. The results show that the extraction yield of naphthoquinone pigments by USWE was the highest, up to 0.31%, while the yields achieved by SE and SCE were 0.21 and 0.19%, respectively. The 6 major compounds were detected in these 3 extract samples but the USWE sample contained the fewest impurities. The extracts obtained with USWE showed the best inhibitory effects on Escherichia coli and Staphylococcus aureus, followed by that with SE. However, the extracts obtained with SE showed the highest DPPH scavenging capacity and reducing action.