Research Article Antioxidative and synergistic effects of bene kernel and hull oils during oxidation of virgin olive oil Reza Farhoosh, Mohammad Hossein Haddad Khodaparast, Ali Sharif, Seyedeh-Zohreh Hoseini-Yazdi and Atefeh Zamani-Ghalehshahi Ferdowsi University of Mashhad, Faculty of Agriculture, Department of Food Science and Technology, Mashhad, Iran Total amounts of conjugated diene hydroperoxides and carbonyl compounds of a virgin olive oil (VOO) and its purified form as affected by 0.1–6% w/w bene kernel (BKO) and hull (BHO) oils were monitored during 16 h heating at 1808C. The VOO was more prone to the production of off-flavour carbonyl compounds than to the formation of conjugated diene hydroperoxides. The VOOs oxidative stability decreased significantly due to the removal of the indigenous antioxidative compounds. Oxidative stability, especially regarding the secondary oxidation, significantly improved with increasing concentrations of the BKO than with those of the BHO. Keywords: Bene / Carbonyl value / Conjugated diene value / Synergism / Virgin olive oil Received: April 4, 2012 / Revised: June 13, 2012 / Accepted: July 11, 2012 DOI: 10.1002/ejlt.201200135 1 Introduction Olive oil is a highly appreciated edible oil for potential health benefits that have been attributed to the fatty acid compo- sition, mainly due to the high content of oleic acid and also to the balanced ratio of saturated (SFA) and unsaturated fatty acids. In addition, olive oil presents considerable amounts of natural antioxidant constituents that are considered to be important in the prevention of many diseases [1]. The fatty acid composition and significant amounts of stability- and health-promoting components, especially phenolic antioxi- dants, have made olive oil a very oxidatively stable amongst heating oils and fats [2]. Lipid oxidation leads to the formation of a series of primary oxidation products named hydroperoxides. Hydroperoxides, which have been described as supporting conjugated diene structures, are generally unstable and decompose into a variety of secondary oxidation products, including carbonyl compounds as the most important ones. It is well known that hydroperoxides do not contribute to fla- vour, whereas carbonyl compounds are mainly responsible for the typical rancid off-flavours [3]. Our previous study indicated that olive oils are more prone to the production of off-flavour carbonyl compounds than to the formation of conjugated diene hydroperoxides [4]. The addition of antioxidants is one of the most well- known strategies applied to delay lipid oxidation reactions. Antioxidants per se are able to considerably increase the oxidative stability of lipid systems, but in many cases, the observed improvement in the resistance of vegetable oils to the oxidation process can be attributed to the synergism between the added antioxidative compounds and those indigenous of the lipid systems. The oils from the kernel and hull of bene (Pistacia atlantica subsp. mutica), which is one of the most widely distributed wild species of pistachio, have been considered amongst very oxidatively stable and powerful natural antioxidative oils [5–9]. Hence, the aim of this study was to determine the inhibition effect of bene kernel (BKO) and hull (BHO) oils on the production of conjugated diene hydroperoxides and off-flavour carbonyl compounds during oxidation of olive oil, and to evaluate the synergism between the BKO/BHO and the indigenous antioxidatve fraction of olive oil. Correspondence: Dr. Reza Farhoosh, Ferdowsi University of Mashhad, Faculty of Agriculture,Department of Food Science and Technology, P.O. Box 91775-1163, Mashhad, Iran E-mail: rfarhoosh@um.ac.ir Fax: þ98-511-8787430 Abbreviations: BKO, bene kernel oil; BHO, bene hull oil; CDV, conjugated diene value; CV, carbonyl value; DNPH, 2,4-dinitrophenylhydrazine; IAC, indigenous antioxidative compound; MUFA, monounsaturated fatty acid; OS, oxidative stability; PUFA, polyunsaturated fatty acid; PV, peroxide value; PVOO, purified virgin olive oil; SFA, saturated fatty acid; TP, total phenolics; TT, total tocopherols; VOO, virgin olive oil Eur. J. Lipid Sci. Technol. 2012, 000, 0000–0000 1 ß 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.ejlst.com