Contents lists available at ScienceDirect Industrial Crops & Products journal homepage: www.elsevier.com/locate/indcrop Optimization of ultrasonic-assisted extraction (UAE) of phenolics and antioxidant compounds from rhizomes of Rheum moorcroftianum using response surface methodology (RSM) Aseesh Pandey a,b , Tarun Belwal a , K. Chandra Sekar a , Indra D. Bhatt a, ⁎ , Ranbeer S. Rawal a a G. B. Pant National Institute of Himalayan Environment and Sustainable Development, Kosi-Katarmal 263643, Almora, Uttarakhand, India b G. B. Pant National Institute of Himalayan Environment and Sustainable Development, Sikkim Unit, Pangthang, Gangtok 737101, Sikkim, India ARTICLE INFO Keywords: Antioxidants Extraction optimization Himalaya Polyphenols Rheum UAE ABSTRACT This study for the first time designed to optimize the extraction of polyphenolic compounds from rhizomes of Rheum moorcroftianum using response surface methodology (RSM). Solvent was selected based on the pre- liminary experiments, and a four-factors-three-level, Box–Behnken Design (BBD) including 29 experimental runs. The polyphenolic content and antioxidant activity was significantly (p < 0.05) affected by vessel diameter – 6 cm (X 1 ), sample to solvent ratio – 1:28.42 g/mL (X 2 ) and extraction temperature – 37.11 °C (X 3 ) under ultrasonic assisted extraction (UAE). The measured parameters were found in accordance with the predicted values. High Performance Liquid Chromatography (HPLC) analysis in optimized condition revealed the presence of 12 phenolic antioxidant compounds with the highest concentration of chlorogenic acid (26.68 mg/g). The results indicate that optimization of extraction conditions in R. moorcroftianum is critical for precise quantifi- cation of antioxidant phenolics and its further utilization in industry. 1. Introduction The genus Rheum consists of approximately sixty species (Rokaya et al., 2012); cultivated for culinary, ornamental and medicinal pur- poses across the world (Arvindekar and Laddha, 2016), and used in the preparation of jams, jellies and wine (Clementi and Misiti, 2010). In Indian Himalayan Region (IHR), the genus Rheum is represented by 10 species and distributed between 2800–4700 m asl (Uniyal et al., 2002; Tabin et al., 2016). Rheum moorcroftianum Royle (Family – Poly- gonaceae), is a Himalayan endemic species commonly known as rhu- barb, grows in rocky, bouldery slopes and river banks between an elevation range of 3200–4700 m asl (Uniyal et al., 2002; Rana and Samant, 2010). The genus Rheum has been used in the traditional Chinese medicine, Medieval Arabic and Ayurvedic system of medicine (Xiao et al., 1984; Arvindekar and Laddha, 2016). Traditionally, the roots and rhizomes of the Rheum are used as an astringent, purgative, tonic and in the healing of ulcers (Anonymous, 2005). Rhubarb con- tains a variety of bioactive compounds like flavonoids, anthraquinone glycosides, tannins, volatile oils and saponins (Ye et al., 2007; Aslam et al., 2012) and contribute to various pharmacological activities like antifungal, antioxidant, hepatoprotective, nephroprotective and im- mune modulatory activities (Zargar et al., 2011). Further, anti-can- cerous properties of the Rheum rhizome in human breast carcinoma (MDAMB-435S) and liver carcinoma (Hep 3 B) cell lines is reported (Rajkumar et al., 2011a,b). The medicinal properties of medicinal plants are attributed to the presence of secondary metabolites, which are unique resources for pharmaceuticals, nutraceuticals, food additives, and fine chemicals (Zhao et al., 2005). These compounds exist in plants and enclosed by insoluble structures such as the vacuoles of plant cells and lipoprotein’s bilayers which complicate their extraction process (Corrales et al., 2008). The nature of bioactive compounds and the presence of other biomolecules along with several factors such as extraction methods, type of solvent, pH, temperature, sample-solvent ratio and extraction time are reported to affect yield (Cacace and Mazza, 2003; Chirinos et al., 2007; Ng et al., 2012; Belwal et al., 2017b). However, there is no universally standardized set of optimum conditions for the extraction of bioactive compounds from different plants (Chirinos et al., 2007; Chen https://doi.org/10.1016/j.indcrop.2018.04.019 Received 4 December 2017; Received in revised form 3 April 2018; Accepted 8 April 2018 ⁎ Corresponding author. E-mail address: idbhatt@gbpihed.nic.in (I.D. Bhatt). Abbreviations: ABTS, 2, 2-Azinobis (3-ethylbenzothiazoline-6-sulphonic acid); AAE, Ascorbic acid equivalent; BBD, Box–Behnken Design; CV, Coefficient of variation; DPPH, 2, 2- Diphenyl-1-picryhydrazyl; FRAP, Ferric reducing antioxidant power; GA, Gallic acid; GAE, Gallic acid equivalent; HPLC, High performance liquid chromatography; Q, Quercetin; QE, Quercetin equivalent; RSM, Response surface methodology; TAE, Tannic acid equivalent; TFC, Total flavonoid content; TPC, Total phenolic content; TPTZ, 2, 4, 6-Tripyridyl-s-triazine; TTC, Total tannin content; UAE, Ultrasonic assisted extraction Industrial Crops & Products 119 (2018) 218–225 0926-6690/ © 2018 Elsevier B.V. All rights reserved. T