There is compelling epidemiological evidence that fruit and vegetable consumption plays an important role on inhibiting development of chronic disorders such as cancer and cardiovascular diseases (Doll, 1990; Hertog et al., 1996). The chemopreventive role of fruits is associated with their phytonutrient contents bearing antioxidative properties (Davidson & Touger-Decker, 2009). Of the antioxidant compounds, phenolics drew significant attention in recent years for their ability to scavenge free radicals generated within cell (Middleton et al., 2000; Yang et al., 2001). Phenolic compounds protect human body by neutralising destructive effect of free radicals on plasma membrane, organelle membranes and DNA (Issa et al., 2006; Villano et al., 2007). Presence of hydroxylated aromatic ring(s) is a common feature of phenolic compounds that are widely distributed in plants (Boudet, 2007). Hydroxyl groups linked to aromatic rings are associated with the formation of electron-rich environment that scavenges the reactive oxygen species (ROS) excluding them from reacting nucleophilic centres in plasma membrane, cellular proteins and DNA (Issa et al., 2006). Phenolic compounds produced by plants are divided into two major groups: phenolic acids and flavonoids. Cinnamic acids and benzoic acids are the two main groups of phenolic acids. Anthocyanidins, flavons, flavonols, flavonons, catechins and proanthocyanidins are the subgroups of flavonoids (Cemeroğlu, 2009). The general phenylpropanoid pathway is responsible for biosynthesis of a substrate common to many of the phenylpropanoid compounds such as flavonoids, monolignols, hydroxycinnamic acids, sinapoyl esters, coumarins and stilbenes (Vermerris & Nicholson, 2006). Therefore, phenylpropanoid pathway serves as a rich source of natural compounds including flavonoids, coumarins and lignans (Fraser & Chapple, 2011).
Many reports in the literature concentrated on the determination of the natural sources of phenolics and their possible health benefits on the living organisms (Knekt et al., 1996; Gil et al., 2002; Liu et al., 2002). Fruits, especially red ones, were determined as to be the dietary sources containing high amount of bioactive phenolic compounds. Thus, pomegranates have received considerable interest in recent years because of their abundant bioactive natural compound contents such as vitamin C, flavonoids, gallotannins, cyanidin, pelargonidin, delphinidin glycosides (Gil et al., 2000; Seeram et al., 2006; Tzulker et al., 2007; Mousavijenad et al., 2009), and regular consumption of pomegranate is associated with cancer chemotherapeutic effect (Malik et al., 2005) and prevention of chronic inflammation (Newman & Ephraim, 2007). Pomegranate fruits are rich source of bioactive compounds and thus have higher antioxidant activity compared with red wine and green tea (Gil et al., 2000). The most influential factors that could affect the content and composition of bioactive molecules in pomegranate are genetic heterogeneities, varietal factors, climate conditions, soil structure, agricultural practices, water–heat stress, harvesting time and storage conditions. Pomegranate fruit (Punica granatum L.) is native to the area surrounded by Persia, Babylon, Anatolia and has been grown in Iran, Southeastern Europe, Mesopotamia and India since ancient times. Turkey is one of the prominent pomegranate producers, and the total pomegranate production of Turkey reached 217 572 tons in 2011 (Anon, 2012) that corresponds to one of the largest pomegranate economies in the world. Turkish pomegranate fruit is being used for the industrial manufacturing of wide range of food products such as fruit juice, concentrate, jam, candies, toppings and canned arils besides its fresh consumption.
As Turkey is one of the world's biggest pomegranate producers and exporters, it is imperative to characterise the antioxidant properties of Turkish pomegranate varieties and determine their inhibitory activity on the development of cancer cell lines. Although there are some reports in the literature describing antioxidant capacities of Turkish pomegranates (Ozgen et al., 2008; Gözlekçi et al., 2011; Caliskan & Bayazit, 2012.), there is no study assessing antiproliferative activities of pomegranates growing in the region. The objective of this study was to identify relationship between colour, phytochemical content and antioxidant activity of four Turkish pomegranate varieties and evaluate antiproliferative–antioxidant activities of their extracts.