Original article Polyphenols content and antioxidant activity of Ghure (unripe grape) marc extract: influence of extraction time, temperature and solvent type Saeedeh Shojaee-Aliabadi, 1 Seyede M. Hosseini, 1 * Brijesh Tiwari, 2 Maryam Hashemi, 1,3 Ghasem Fadavi 1 & Ramin Khaksar 1 * 1 Department of Food Science and Technology, Faculty of Nutrition Sciences and Food Technology, National Nutrition and Food Technology Research Institute, Shahid Beheshti University of Medical Sciences, Tehran, Iran 2 Hollings Faculty, Manchester Food Research Centre, Manchester Metropolitan University, Manchester, UK 3 Department of Microbial Biotechnology and Biosafety, Agricultural Biotechnology Research Institute of Iran, Karaj, Iran (Received 19 December 2011; Accepted in revised form 6 August 2012) Summary The objective of this study was to optimise the temperature (25–50 °C), time (1–24 h) and the solvent ratio (ethanol/water, 0–100%) for the phenolic compounds extraction of Ghure marc (unripe grape) using response surface methodology. The central composite design (CCD) generated satisfactory models for the optimisation of process variables. The results revealed that the ratio (X 3 ) was the most significant parame- ter on total phenolic content (TPC) and antioxidant activity [% 2-diphenyl-1-picrylhydrazyl (DPPH)], and there was a significant correlation between TPC and antioxidant activity. The optimal conditions for tem- perature and time were 44.93 °C and 19.34 h, respectively, and the ratio of ethanol to water was 70.08, which verified with carrying out confirmatory experiments. Under this condition, TPC and %DPPH were 388.79 mg GAE per 100 g and 91.01, respectively. The results of this study revealed that the Ghure marc can be used as a low-cost source of natural antioxidant in food. Keywords Antioxidant, extraction, Ghure (unripe grape), response surface methodology. Introduction Reactive free radicals that are generated during normal and abnormal cellular metabolism may cause cell death and tissue damages such as disruption of mem- brane fluidity, protein denaturation, lipid peroxidation and the oxidation of DNA. In addition, lipid peroxi- dation is one of the major causes of food deterioration during processing and storage. Antioxidants have been widely used as food additives to provide protection against the oxidative degradation of foods by free rad- icals. Because of toxicological effects and suspected carcinogenic potential of synthetic antioxidants, such as BHA and BHT, great interest has been recently aroused in the usage of natural antioxidants in food industries (Kouri et al., 2007; Spigno & Faveri, 2007). Plant phenolic compounds include different classes such as flavonoids and phenolic acids that have the ability to scavenge free radicals, that is, antioxidant capacity (Chirinos et al., 2007). Grape is an appraisable source of antioxidants such as phenolics, flavonoids and anthocyanins (Go¨ktu¨rk Baydar et al., 2007; Wang et al., 2010). Although the bioactive compounds and the antioxidant activities of grapes have been the subject of many investigations, Ghure (unripe grape) has been scarcely studied for these compounds (Karapinar & Sengun, 2007). It has been shown that the antioxidant activity of organic grapes was 5.70 mM Trolox per g 30 days before har- vest and reduced about 18% on the date of harvest (4.70 mM Trolox per g) (Mulero et al., 2010). Unripe grape, which is called Ghure, is used in the form of either whole fruit or juice as a popular acidify- ing and flavouring agent in many foods such as salads and soups in Iran and neighbouring countries. Ghure juice and its powder are also used to reduce blood pressure and lipids as well as body weight in tradi- tional medicine. It has been reported that Ghure juice has no hypercholesterolaemia effect and may inhibit atherosclerosis by other mechanisms rather than modifying lipid levels (Aminian et al., 2003). Another study showed that Verjuice (Ghure juice) had protective effect against some of the risk factors of *Correspondent: Fax: +98 21 22376480; e-mails: Sm_hosseini@nnftri.ac.ir; r.khaksar@sbmu.ac.ir International Journal of Food Science and Technology 2013, 48, 412–418 doi:10.1111/j.1365-2621.2012.03203.x © 2012 The Authors. International Journal of Food Science and Technology © 2012 Institute of Food Science and Technology 412