30A-26 |
Phenolic compounds of Lianolia virgin olive oil and their alteration during storage |
O. I. OKOGERI, Dept of Chemistry, University of Ioannina, Ioannina, 45110, Greece and M. Tasioula-Margari. The level of phenolic compounds is a very important parameter in the evaluation of virgin olive oil quality since they are related to the oil’s resistance to oxidation. These substances have also been reported as having beneficial biological activity. The objective of this work was to monitor the alteration as well as the antioxidant effectiveness of phenolic compounds during long term storage of virgin olive oil in diffused light and in the dark. Virgin olive oil samples of Lianolia variety were used. Samples were stored at room temperature, under diffused light for six months, and in the dark for twelve months. The phenolic fraction was periodically extracted from stored oil samples and analyzed by reversed-phase HPLC using UV detection. Antioxidant effectiveness of phenolic compounds was monitored by measuring peroxide values (PV). Simple phenols (Fraction I): hydroxytyrosol, tyrosol, vanilic acid, syringic acid, p-coumaric acid and o-coumaric acid as well as complex phenols: hydroxytyrosol derivative (Fraction II) and tyrosol derivative (Fraction II) were the main phenolic compounds identified. A remarkable change was observed in all three fractions after six months storage under diffused light. During this period an average decrease of 76%, 62%, and 42% were recorded for fractions I, II and III respectively. PV ranged from 18.57-29.65 meq/kg. The rate of alteration was generally slower in the dark. Fraction I consisting of simple phenols decreased by an average of 67% in twelve months while fractions II and III consisting of hydroxytyrosol and tyrosol derivatives decreased by 46% and 26% respectively. PV ranged between 17.93 and 30.43 meq/kg. Remarkable amounts of phenolic compounds were present even when PV exceeded the upper limit of 20 meq/kg. This suggests that the biological value of virgin olive oil is significantly maintained during storage.
Session 30A, Food Chemistry: Lipids
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