Available free online at www.medjchem.com Mediterranean Journal of Chemistry 2019, 7(4), 423-432 *Corresponding author: Hamid Mellouk Received June 5, 2018 Email address: hmellouk17@gmail.com Accepted July 2 , 2018 DOI: http://dx.doi.org/10.13171/mjc76198121610hm Published December 16, 2018 Extraction of phenolic from Moroccan grape pomace: Optimization of decoction extraction of phenolic compounds using response surface methodology Safae El Alami El Hassani, Anas Driouich, Hamid Mellouk, Bouchra Bejjany, Adil Dani and Khalid Digua Laboratory of Process Engineering and Environment, Faculty of Science and Technology Mohammedia, Hassan II University, BP 140 Mohammedia, Morocco Abstract: The present study focuses on the optimization of the parameters to extract phenolic products by decoction and the quantification of these compounds from grape pomace, using a central experimental design. The antioxidant activity of methanolic extracts from grape skin grown in Morocco was evaluated. The grapes variety is “Michael Paleiri”, it is a black variety with pips, and they are from the region of Benslimane. The total phenolic compounds contents were determined by the Folin-Ciocalteu method. The optimization suggested that extraction with methanol for 29 min, at 60 °C were the best solutions for this combination of variables. The largest amount obtained was 1042.06 mg EGA/g DW. The antioxidant activity is carried out by the radical scavenging method 1,1-diphenyl-2-picryl hydrazyl (DPPH°) and the ferric iron reduction capacity (FRAP). The DDPH inhibition capacity reached 20.78%, compared with 15.22% of a BHT solution at 0.001 g/L. A significant relationship between antioxidant capacity and total phenolic content is evident (R 2 =0.994). These results demonstrate that methanol extracts from the waste from grapes grown in Morocco could be used as potential sources of natural extracts rich in phenolic compounds and endowed with significant antioxidant activity. Keywords: Grape pomace, Phenolic compounds, Antioxidant activity, Response surface methodology. Introduction There is growing interest in the use of residues generated by the wine and grape industries. In recent years, grape pomace is used as soil conditioner and fertilizer, as an adsorbent for heavy metals. Moreover, it is used in the food industry and the production of pullulan 1 . The skins of grapes are the only industrial source for tartaric acid production which is used as an additive in medicines and cosmetics, as acidulant and compound in soft drinks 2 . In particular, waste from vineyards could be an alternative source for obtaining natural antioxidants without any negative effects in comparison to synthetic antioxidants. Grape pomace represents a rich source in bioactive molecules with the high added value that can be applied in many industries 3 . Moreover, it is characterized by high levels of a total phenolic compound and total flavoinds 4,5 . For this reason, large quantities of phenolic compounds remain in the by-products of wine and grape juice, and there is a great interest in exploiting this type of grape by-products to obtain potentially bioactive phenolic compounds 5,8 . Antioxidants are potent free radical scavengers and serve as inhibitors of neoplastic processes 9 and allow the body to fight against aggressions of oxygen which are at the origin of a large number of diseases, which is attracting more and more interest in the prevention and treatment of cancer 10 . Furthermore, antioxidants have anti-inflammatory activity 11,12 , cardiovascular 13,15 , neurodegenerative-protective activities 16 antineoplastic and antihepatotoxic 17 . Various antioxidants are provided to cells through diet; vitamin E wich is present in grape seeds can prevent lipid peroxidation of plasma membrane 18 . Several methods are used for the extraction of polyphenolic compounds (TPC). According to Soural et al. (2015) 19 , extraction of TPC from grape can give different stilbene yields according to the process employed using several organic solvents. The best yields are obtained by decoction with methanol; other innovative processes have been carried out, such as fluidized bed extraction or reflux extraction, which give similar yields of the decoction, but new techniques such as accelerated solvent extraction or assisted extraction by microwave give higher yields of phenolic compounds. However, there is no single solvent or method optimal to extract all TPC from grape pomace, TPC