Contents lists available at ScienceDirect Industrial Crops & Products journal homepage: www.elsevier.com/locate/indcrop Comparison study for the recovery of bioactive compounds from Tribulus terrestris, Panax ginseng, Gingko biloba, Lepidium meyenii, Turnera diffusa and Withania somnifera by using microwave-assisted, ultrasound-assisted and conventional extraction methods C. Tsaltaki, M. Katsouli, T. Kekes, S. Chanioti, C. Tzia* Laboratory of Food Chemistry and Technology, School of Chemical Engineering, National Technical University of Athens, 5 Iroon Polytechniou St., 15780, Zografou, Greece ARTICLEINFO Keywords: Ultrasound assisted extraction Microwave-assisted extraction Heat refux extraction Soxhlet HPLC Herbs ABSTRACT Heat refux (CONV), Soxhlet (SOX), microwave-assisted (MAE) and ultrasound-assisted (UAE) extraction methods, using ethanol, water and their mixtures, were studied for the recovery of bioactive compounds from Tribulus terrestris, Panax ginseng, Gingko biloba, Lepidium meyenii, Turnera diffusa and Withania somnifera. The study revealed that SOX method achieved extracts with the highest yield TPC in terms of the total phenolic content (TPC) (66.65 ± 1.50%); MAE and UAE resulted also in extracts with high TPC and shorter treatment times compared to SOX. More specifcally, the TPC values for MAE and UAE were 91.783 ± 0.026 mg GA/g dw and 81.113 ± 0.103 mg GA/g dw, respectively, the antioxidant activity (DPPH) was 63.577 ± 0.057 mg Trolox/g dw and 64.923 mg Trolox/g dw, and the yield TPC was 60.82% and 61.89%, respectively. All were higher compared to those obtained by the CONV method. The use of pure ethanol as the extraction solvent, provided maximum TPC and similar results for DPPH and yield TPC (%). Moreover, maximum TPC (183.70 mg GA/g dw) and DPPH (377.21 mg Trolox/g dw) values were achieved for T. diffusa. The HPLC analysis of T. terrestris, P. ginseng and G. biloba extracts showed that G. biloba contained its characteristic bioactive compound in the highest concentration (13.512 mg gingkolide/g herb). 1. Introduction An increasing interest has been observed towards the use of com- plementary and alternative herbal medicine by the general public worldwide. Plant-based drugs or supplements are already used for the treatment of skin diseases, mental disorders and many other infectious diseases (Zhang et al., 2015). According to the World Health Organi- zation (WHO), the majority of the population in developing countries relies almost totally on herbal medicine for their primary health care needs. In particular, the herbal market such as the trade in medicinal plants, herbal raw materials, and herbal drugs presents a decent annual growth rate of 15% (Ahmad Khan and Ahmad, 2019; Chandrasekara and Shahidi, 2018). The increasing popularity and acceptability of herbal medicines are based on the belief that all-natural products are safe, cheap, and commonly available. However, there are also some concerns associated with herbal medicines regarding their standardi- zation compared to conventional drugs. Recently, the research eforts have been intensifed in both developed and developing countries to scientifcally evaluate and validate the herbal drugs based on clinical trials (Kamohara et al., 2014). Food or beverage products, enriched with herbal extracts and con- sumed as part of a balanced diet, may enhance the intake of antioxidant and the overall health status of humans. This rapidly growing segment of herbal products is based on the assumption that their natural bioactive compounds render a number of diversifed biological efects, such as antioxidant, antibacterial, antiviral, anti-infammatory and antiallergic activity, as well as weight loss, aphrodisiac efects against erectile dysfunction and a number of other cosmetic purposes (Zhao et al., 2018). Thus, the use of herbs as an essential ingredient of bev- erage or food products represents an area of vast interest, since they are an important source of functional compounds with unique mechanisms of action against diseases and other human body dysfunctions. Plant species, such as Tribulus terrestris, Panax ginseng, Gingko biloba, Lepidium meyenii (Maca), Turnera diffusa leaf (Damiana) and Withania somnifera (Ashwagandha) have been tested for the potential develop- ment of natural formulations against diferent disorders or https://doi.org/10.1016/j.indcrop.2019.111875 Received 5 June 2019; Received in revised form 18 September 2019; Accepted 16 October 2019 ⁎ Corresponding author. E-mail address: tzia@chemeng.ntua.gr (C. Tzia). Industrial Crops & Products 142 (2019) 111875 0926-6690/ © 2019 Elsevier B.V. All rights reserved. T