Murdoch, Travis Michael (2020) Investigation of Quality Parameters in Australian Olive Oils for Authentication. PhD thesis, Victoria University.

Abstract

The authentication of extra virgin olive oils (EVOOs) is of importance due to the potential economic impacts on the global market when olive oils are diluted with other edible oils. The International Olive Council stipulates a wide range of methods to authenticate EVOOs, however, these methods are subject to limitations. This research addresses certain weaknesses associated with these methods such as the analysis time, consistency and reliability of the official methods. A series of techniques and EVOO chemical parameters that could be used to supplement current authentication techniques was investigated. In particular, the "quality" parameters comprising total phenolic content, antioxidant capacity and tocopherol composition of Australian EVOOs diluted with canola, sunflower and rice bran oil were investigated along with the study of the UV and fluorescent spectra of these mixtures. A framework was developed which combines the strengths of the tests methods to propose a scheme to identify an adulterated EVOO. The total phenolic content measured by the Folin-Ciocalteu assay provides a positive test for the presence of a diluent at concentrations of >5% w/w but is unable to identify the diluent and is non-linear with concentration. The total phenolic content as determined by high-performance liquid chromatography using a diode-array detector that has a similar detection limit to the Folin-Ciocalteu assay and is unable to identify the diluent but provides better linearity at diluent concentrations of >10% w/w. The antioxidant capacity of diluted EVOOs using the radical 2,2 diphenyl-1-picrylhydrazyl (DPPH) is only suitable for rice bran or canola oil diluents at 10% w/w and 20% w/w, respectively but in certain cases can identify the diluent oil in the mixture. A novel technique in which the UV and fluorescent profiles of the EVOOs mixtures were determined and provided a rapid, non-destructive analysis of the EVOOs. Concurrent scans of both the excitation and emission spectra between 250 and 800 nm enabled the unique identification of EVOOs, canola, sunflower and rice bran oils Furthermore, selected excitation wavelengths of 328 nm and 536 nm were used to identify EVOO that was diluted with 5% w/w sunflower oil. The total tocopherol concentration can be used to identify 10% w/w mixtures of sunflower and canola oil in EVOO however this parameter is not suitable to identify the presence of rice bran oil. Nonetheless, a strong correlation was found between the compositional changes to α- and γ-tocopherol upon dilution which enabled the detection of diluted EVOOs, and these tocopherol concentrations were found to offer a unique profile for all three diluent oils. For example, a γ-tocopherol concentration exceeding 10 mg kg-1 suggests the EVOO is diluted with canola or rice bran oil at a concentration of 5% w/w or 10% w/w, respectively. An α-tocopherol concentration exceeding 178 mg kg-1 suggests the EVOO is diluted with sunflower oil at a concentration between 5-10% w/w depending on the EVOO. Overall, the α- and γ-tocopherol profiles were used to develop a decision tree framework to identify and quantitate the diluent oil. In combination, the above traditional methods used with the novel techniques and the assessment framework developed in this work enable a more robust assessment to be made of the authenticity of EVOOs in the future.

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