Introduction: The term antioxidant is said to be compounds that are delaying or preventing oxidization of a substance at their own presence, which leads to reach a stabilized food quality (Collins, 2005). Natural antioxidants are often phenolic compounds that exist in all parts of a plant. These compounds are secondary metabolites that can inhibit active oxygen species by giving hydrogen atoms and converting them into more stable non-radical compounds due to oxidation and reduction properties. They also have the ability to chelate the metals (Wijngaard et al., 2009 and Erasto et al., 2007). Regarding the positive effects of natural antioxidants, many studies have been conducted to extract, identify and apply them from various herbal sources. Edible fruit jujube is a member of the Ramanaceae family, known in Iran as the jujube. The plants of the family are jujube flowers, which are all diploid and have 24 chromosomes. The jujube tree has been cultivated in China for thousands of years ago and is used as a medicine, food and food flavoring, also distributed in tropical and subtropical regions of Europe, Australia and South Asia. (Su et. al., 2005, Yan et. al., 2002, Preeti et al. 2014). Phenolic compounds have a high potential for antioxidants and a natural source of antioxidants. The antioxidant capacity of the Jujube is due to its antioxidant compounds such as flavonoids, total phenolic, anthocyanins and ascorbic acid. Zhao et al., 2014) and Zhang et al., 2010). Shell, pulp and fruit jujube seeds have a wide range of phenolic compounds and have long been used as a drug and flavor agent (Zhang et. al., 2010, Mahajan et al., 2009). Many studies have investigated the effects of Jujube fruit and its juice on the prevention and treatment of diseases such as digestive disorders, weakness, obesity, liver problems, diabetes, skin infections, Infections, Anemia, and Allergies have been reported (Gao et al., 2015 and 2013, Kim et al., 2011, Verma, 2016, Li et al., 2012). In a study by Wang et al. on Jujube fruit, 22 compounds were identified in ethanol jujube extracts (Wang et al., 2014). Zhang et al. The study that they carried out showed that the antioxidant activity of the jujube is due to its antioxidant compounds, such as flavonoids, total phenolic, anthocyanidins and ascorbic acid (Zhang et al., 2010). Italian scientists influence the phenolic compounds of jujube fruit extract on breast cancer cells (Plastina et al., 2012). During a study conducted in Egypt, the effect of jujube fruit on obesity, lipid profile and liver function were examined. (Mostafa et al., 2013). In another study on juvenile fruit phenolic compounds, the effect of jujube on seizure treatment was evaluated and the results showed that jujube has protective properties against seizure, oxidative stress and other disorders. Pahuja et al., 2011).
In this research, extraction of phenolic compounds of Ziziphus Jujuba extracts has been performed using the supercritical carbon dioxide fluid method and optimization of the extracted compounds and the measurement of the antioxidant activity of Jujube fruit.
Materials and methods: Jujube fruit was prepared from Birjand in late August. Chemical materials such as pure ethanol, reagent Folin-Cictalto, sodium carbonate and free radical molecules from German-German corporations and Sigma Aldrich, and laboratory glassware and instruments such as volumetric balloons, refrigerators and freezers, spatula, vertex, buret, pipettes, calibrated cylinders, Filter paper, Falcon, Human Dimension, Mesh 30, Funnel and Arlene were provided. The freshly purchased fruits were separated from the tree before drying. After separating the jujube grain, the fruit was dried at 40°C in a digital-powered oven (volume 5 liters made by Binder Company in Germany), and dried with the aid of a home-made mill. For particles of uniform size, the resulting powder was sown using a mesh 30 and kept in a refrigerator at -20°C until it was extracted.
Results & discussion: Generally, according to the results of both solvent extraction and supercritical fluid extraction (SFE) methods, the total amount of phenolic extraction at the optimal point in terms of mg Gallic acid to gram of dry extract in the solvent extraction and in the supercritical method were 26.21 and 2.24, respectively. Comparison of the obtained values at the optimal point of both methods indicated that the solvent method shows higher values of the total phenol content and it has been more successful. However, due to the insignificant differences in total extraction phenol content between the two methods, the supercritical method can be described as a better way to extract phenolic compounds, since the supercritical method was less effective than antioxidant power despite the presence of phenol, because in the supercritical method, the selectivity can be increased and the target compounds can be isolated by adjusting the temperature and pressure which increases the purity and increase the antioxidant property, and the purpose of the extraction of phenolic compounds. On the other hand, due to the low amount of organic solvent used in this method and the reduction of health and environmental risks, the supercritical method can be introduced as an effective method for extraction of phenolic compounds from Ziziphus Jujube fruit, which reduces the consumption of organic solvent and causes in an efficiency equal with solvent method approximately. In general, according to the amount of total phenolic extraction in both methods, it can be said that Jujube has higher phenol content than other herbs and it can be introduced as a natural antioxidant at the commercial level.