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Fourier transform mid-infrared spectroscopy evaluation of early stages of virgin olive oil autoxidation

Authors

  • Nikolaos Nenadis,

    1. Laboratory of Food Chemistry and Technology, School of Chemistry, Aristotle University of Thessaloniki, Thessaloniki, Greece
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  • Ioannis Tsikouras,

    1. Laboratory of Food Chemistry and Technology, School of Chemistry, Aristotle University of Thessaloniki, Thessaloniki, Greece
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  • Polidoros Xenikakis,

    1. Laboratory of Food Chemistry and Technology, School of Chemistry, Aristotle University of Thessaloniki, Thessaloniki, Greece
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  • Professor Maria Z. Tsimidou

    Corresponding author
    • Laboratory of Food Chemistry and Technology, School of Chemistry, Aristotle University of Thessaloniki, Thessaloniki, Greece
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Correspondence: Professor Maria Z. Tsimidou, Laboratory of Food Chemistry and Technology, School of Chemistry, Aristotle University of Thessaloniki, 541 24, Thessaloniki, Greece

E-mail: tsimidou@chem.auth.gr

Fax: +30 2310 997779

Abstract

The applicability of FT-MIR/ATR spectroscopy (4000–400 cm−1) for the evaluation of early stages of autoxidation was examined for extra virgin olive oil samples (EVOO), which even after 12-month storage (dark, 23 ± 3°C) satisfied official limits for acidity, peroxide, K232 and K270 values. Changes in intensity values at 3470 cm−1 (hydroperoxide formation) and in values of various intensity ratios, namely A3006/2924, A3006/2853, A3006/1746, A3006/1465, A3006/1163, A1118/1097, A2853/1746, A2853/1417, A2853/1163, A2853/1118, A2853/1097, and A2853/723 (relevant to the degree of oil unsaturation) did not offer more information than the physicochemical criteria when examined one by one. Principal component – discriminant analysis of intensity values at 2924, 2853, 1746, 1465, 1163, 1118, 1097, and 723 cm−1 led to a 100, 91, and 54.5% correct classification for the 12, 6, and 0 months stored ones, respectively. Improvement in correct classification of the latter (73–91%) was obtained when the second derivatives of various spectral ranges were treated by the same statistical approach. Frequencies assigned to stretching and/or bending of [BOND]C[BOND]O and [BOND]CH2[BOND] groups (1020–1260 cm−1) produced the best discrimination among samples. Findings are discussed with reference to literature reports about FT-MIR applicability under various oxidation conditions of virgin olive oil (VOO). A systematic inter-laboratory study is suggested in order FT-MIR/ATR to be used as a robust tool in VOO quality control.

Practical applications: There is an increasing awareness among consumers and olive oil producers and distributors about virgin olive oil freshness and discussions are on the way for updating of the relevant EU regulations on its quality characteristics. Modernization of methods of analysis and introduction of additional criteria can be achieved by the employment of powerful techniques that can provide solid, multiple type of information with little sample manipulation. FT-MIR/ATR requires no sample preparation, the spectra are related to all chemical components of the lipid matrix and are recorded over a broad region (4000–400 cm−1) in few minutes. Chemometric analysis of the numerous peaks extracts all of the valuable information that can enhance claims or disputes about the oxidative status of a virgin olive oil (e.g., freshness or loss of freshness). Moreover, FT-MIR apparatus has multiple uses in the oil industry (authenticity, origin) so that an investment on such a green technique is advisable.

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