Evaluation of Olive Oil Produced From Some Varieties Growing under Siwa Oasis Condition

The purpose of this study was to evaluate the quality indices and sensory evaluation of olive oil samples extracted from three varieties olive (Olea europaea L.), Frangivento (FOOS), Maraqi (MOOS) and Coratina (COOS) growing in Siwa Oasis, and two varieties olive Maraqi (MOOD) and Coratina (COOD) growing in Desert Rood to identify and classify the oil. The samples which were studied collected from Siwa Oasis and Desert Rood region were examined for physical and chemical properties (acidity, peroxide value, ultraviolet spectrophotometric analysis K232 and K270, fatty acids composition and total phenol content. Olive oil was analyzed for fatty acids commonly present in olive oils which are Palmitic, Palmitoleic, Stearic, Oleic, Linoleic, Linolenic, and Arachidic. Oleic acid was found in high percentage ranged from (71.63% in FOOS cultivar up to 76.00% in MOOD), followed by Palmitic, Linoleic, Stearic, Palmitoleic, and Linolenic. Arachidic acid was detected in all olive oil samples but in low percentage. Oxidative stability by Rancimat method and phenolic compositions by HPLC, were analyzed for each oil samples. Small differences were detected depending on the growing area. In general the main phenolic compound (Oleuropein, Hydroxytyrosol, p-Coumaric and Tyrosol), were present in higher levels in the oil obtained from olive oils under this studied. Big difference was observed for total polyphenols content within the cultivars, total polyphenols of MOOD cultivar olive oil was the highest (211.05 mg/ kg oil) while the lowest (139.31 mg/kg oil) was in the COOS cultivar. Resistance to oxidation was assessed by Rancimat method and showed a good correlation with the amount of total phenols. Also, results of the quality indices (free acidity, peroxide value, k 232 , k 270 and sensory analysis) revealed that, all the analyzed oils were classified into extra virgin category according to IOC 2011 (Trade standard for olive oil). Also, results showed that small differences of quality indices between olive oil samples extracted from five varieties under investigation. showed higher perception of bitterness and fruity than the oils growing in Siwa Oasis. These obtained results demonstrated that there was a good correlation between total polyphenol content and sensory properties of the olive oil. This is confirmed by observations of (Kiritsakis et al., 1998).