Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem Establishment of ultrasound-assisted extraction of phenolic compounds from industrial potato by-products using response surface methodology Ylenia Riciputi a , Elixabet Diaz-de-Cerio b , Hazal Akyol c , Esra Capanoglu c , Lorenzo Cerretani d , Maria Fiorenza Caboni a,e , Vito Verardo f,g, ⁎ a Inter-departmental Centre for Agri-Food Industrial Research (CIRI Agroalimentare), Alma Mater Studiorum-University of Bologna, via Quinto Bucci 336, 47521 Cesena, FC, Italy b Department of Analytical Chemistry, University of Granada, C/Fuentenueva s/n, 18071 Granada, Spain c Department of Food Engineering, Faculty of Chemical and Metallurgical Engineering, Istanbul Technical University, Ayazağa Campus, 34469 Maslak, Istanbul, Turkey d Pizzoli SpA, via Zenzalino Nord 1, 40054 Budrio, Bologna, Italy e Department of Agriculture and Food Sciences, Alma Mater Studiorum-University of Bologna, Piazza Goidanich 60, 47521 Cesena, FC, Italy f Department of Nutrition and Food Science, University of Granada, Campus of Cartuja, 18071 Granada, Spain g Institute of Nutrition and Food Technology ‘José Mataix’, Biomedical Research Centre, University of Granada, Avenida del Conocimiento s/n, E-18071 Granada, Spain ARTICLE INFO Keywords: Potato peel by-products Phenolic compounds Antioxidant activity Response surface methodology Box-Behnken design ABSTRACT Potato processing generates large amounts of by-products, which include potato peels and the outer layers of flesh, which contain phenolic compounds. The purpose of this study was to establish an extraction method for phenolic compounds from industrial potato by-products by using response surface methodology (RSM). Box- Behnken design (BBD) was performed to optimize the extraction conditions of phenolic compounds considering different extraction temperature, ratios of ethanol/water, time of extraction and sample/solvent ratio. The op- timum extraction conditions were obtained with ethanol/water 55/45 (v/v) by ultrasound bath during 35 min at 35 °C and 1/10 sample/solvent ratio. The best conditions were applied to determine the phenolic content in five potato by-products. The analyses by HPLC-DAD-ESI-MS showed that chlorogenic acid accounted for a 49.3–61% of the total phenolic compounds. Positive Pearson correlations between HPLC data and antioxidant activity confirmed that the phenolic compounds had significant antioxidant properties. 1. Introduction Potato is one of the most consumed foods in the world and it also has a wide place of industry. Although the potato cultivated globally belongs to just one botanical species, Solanum tuberosum L., the tubers come from thousands of varieties with great differences in size, shape, colour, texture, flavour and cooking characteristics (FAO, 2008). The global use of potatoes is moving from fresh potatoes to pro- cessed products such as fries, chips, mashed and canned potatoes (Sabeena Farvin, Grejsen, & Jacobsen, 2012; Tierno et al., 2015). After potato processing, a lot of waste is produced as peels, causing handling and storage problems (Singh & Saldaña, 2011). Potato provides noteworthy portions of phenolic compounds lo- cated in the peel and the close tissues. In many studies, it is reported that potato is a good source of phenolics with an antioxidant capacity (Albishi, John, Al-Khalifa, & Shahidi, 2013; Kanatt, Chander, Radhakrishna, & Sharma, 2005; Koduvayur Habeebullah, Nielsen, & Jacobsen, 2010; Mohdaly, Sarhan, Smetanska, & Mahmoud, 2010). Among the reported phenolic components in potato peels, caffeic acid and chlorogenic acid play the main roles in the antioxidant activity (Nara, Miyoshi, Honma, & Koga, 2006; Rodriguez de Sotillo, Hadley, & Holm, 1994; Wu et al., 2012). These components aid to constitute de- fence mechanisms against plant diseases and protect cells from ex- cessive oxidation and free-radical damage. In nutrition, they have re- ceived significant consideration as they contain potentially protective factors because of their potent antioxidant properties (Akyol, Riciputi, Capanoglu, Caboni, & Verardo, 2016; Friedman, 1997; Mäder, Rawel, & Kroh, 2009). Some epidemiological investigations showed a negative correlation between the intake of dietary antioxidant components and diseases, such as atherosclerosis, cancers, faster aging of the body, and heart attacks (Lindberg Madsen, Andersen, Jorgensen, & Skibsted, 2000; Lotito & Frei, 2004; Othman, Ismail, Abdul Ghani, & Adenan, 2007). In this two-stage study, first optimum extraction conditions were https://doi.org/10.1016/j.foodchem.2018.06.154 Received 27 March 2018; Received in revised form 26 June 2018; Accepted 30 June 2018 ⁎ Corresponding author at: Department of Nutrition and Food Science, University of Granada, Campus of Cartuja, 18071 Granada, Spain. E-mail address: vitoverardo@ugr.es (V. Verardo). Food Chemistry 269 (2018) 258–263 Available online 02 July 2018 0308-8146/ © 2018 Elsevier Ltd. All rights reserved. T