Oxidative stability of Purified Common Kilka (Clupeonella cultiventris caspia) triacylglycerols as affected by the Bene kernel and hull oils and their Unsaponifiable matters

Abstract

Introduction: Common Kilka (Clupeonella cultriventris caspia) is one of the most abundant and industrial fish in the Caspian Sea located in the north of Iran, and also the best source of long-chain polyunsaturated fatty acids, especially EPA and DHA [Fazli et al., 2009, Connor, 2000]. Due to high level of the ω3 : ω6 ratio and polyene index, the common Kilka oil is expected to be highly susceptible to oxidation [Pirestani et al., 2010]. The interesting antioxidative characteristics of the oils and unsaponifiable matter (USM) extracted from the kernel and hull of bene fruit (Pistacia atlantica subsp. Mutica) attracted our attention to use them as natural alternatives for stabilizing the common Kilka oil and compare with BHT and α-tocopherol [Farhoosh et al., 2012]. Materials and method: The ripe bene fruits were collected from the fields of Islamabad in the Ilam province. After drying and also grounding to powder, the oils from the kernel (BKO) and the hull (BUO) of bene were extracted with n-hexane (1:4 w/v). Moreover, the USM content of the kernel (UKO) and hull (BHO) oils of bene were determined by the method described by Lozano et al, 1993. Chemical compositions of the bene oils’ unsaponifiable matter were determined by a thin-layer chromatography [Lercker and Rodriguez-Estrada, 2000]. Crude Kilka oil was purified by a multilayer column chromatography to eliminate the majority of pro-oxidant and antioxidant compounds normally present in it. The purified Kilka oil (PKO) was blended separately with 1 and 2% (w/w) of the antioxidative oils (BKO and BHO), 1 and 1.5% (w/w) of the oils’ unsaponifiable matter (UKO and UHO), and 100 mg/kg α-tocopherol and BHT and then exposed to the following stability test. Fatty acid composition of the oil samples was determined by gas-liquid chromatography [Sharina and Jumat, 2006]. The iodine value (IV) was measured according to the AOAC Official Method 920.158 [AOAC, 2005]. A colorimetric method was used to determine total tocopherols (TT) content [Wong et al., 1988]. Total phenolics (TP) content was spectrophotometrically determined using Folin–Ciocalteau’s reagent [Capannesi et al., 2000]. A Metrohm Rancimat model 743 (Herisau, Switzerland) was used for the oil/oxidative stability index (OSI) measurement in airflow rate of 20 L/h. The temperatures in measuring of the OSI were 60 °C for the PKO, OSI60, and 120 °C for the BHO and BKO, OSI120 [Farhoosh et al., 2008a; Mendez et al., 1996]. The analysis of variance (ANOVA) was carried out according to MStatC and SlideWrite software. Significant differences between means were determined by Duncan’s multiple range tests; p values less than 0.05 were considered statistically significant. Results and Discussion: The initial quality parameters of the PKO, BHO and BKO are shown in Table 1. The PKO was mainly constituted of MUFA, followed by the SFA and PUFA, and there was no measurable contents of TP, TT and USM fractions in it. The PKO showed a PUFA/SFA ratio higher than the minimum value recommended by the UK Department of Health (0.73 vs. 0.45) [HMSO. UK., 1994]. The ω3/ω6 ratio of the PKO was relatively similar to that of Indian mackerel (Rastrelliger kanagurta) (1.60 and 1.67, respectively) (Table 1) [Osman, Suriah, & Law, 2001]. The IV, as an indicator of the oil unsaturation and resistance to oxidation, for the PKO (114.99) was much lower than sardine (156.2) and salmon (165.8) oils [Frankel, 1998; Endo, Tagiri-Endo, & Kimura, 2005]. As can be seen in Table 1, the BKO had higher contents of the USM, tocopherols and phenolic compounds than the BHO. The valuable effects of minor components especially polyphenols and tocopherols of the BHO and BKO on the oxidative stability of vegetable oils have been shown in the previous studies [Farhoosh et al., 2012]. The differences in the fatty acid composition and the amounts of minor components led to the greater OSI120 of the BKO than the BHO (9.46 vs. 7.91 h). The major constituents of the UHO and UKO were tocopherols and tocotrienols (Table 2). These compounds, which are particularly important functional constituents of the USM of vegetable oils, have nutritional importance for human health and render antioxidative properties [Lercker and Rodriguez-Estrada, 2000]. The OSI60 values of the PKO as affected by the antioxidative compounds are presented in Fig 1. As shown in Fig. 1, the OSI60 of the PKO (1.66 h) significantly increased in presence of the antioxidants added. Moreover, the highest significant stabilizing effect belonged to the UKO 1.5%, so that it was able to increase significantly the OSI60 up to 8.12 fold (OSI60, 13.48 h) (p < 0.05). Previous findings have demonstrated antioxidant activities of the constituents of the UKO and UHO in vegetable oils. In addition, it has been reported that the fraction of tocopherols and tocotrienols, and terpenoid compounds, particularly triterpenic dialcohols and 4,4'-dimethylsterols, possess antioxidative effects, in overall, better than those of other fractions examined [Farhoosh et al., 2008; Sharif et al., 2009]. Due to the higher amounts of these active fractions (Table 2), the UKO showed higher antioxidative effect on the PKO stability.