**4. Conclusions**

84 Olive Oil – Constituents, Quality, Health Properties and Bioconversions

An interesting study on thermal oxidation of extra virgin olive oils has been published recently (Navarra et al., 2011). Among different experimental techniques (including FTIR and rheology) time-resolved luminescence was used to investigate early steps of the thermally induced oxidative process. The oxidation process was followed at three different heating temperatures (30, 60 and 90C) as a function of time for up to 35 days. The chlorophyll fluorescence lifetime increased from 6.0 ± 0.1 ns, measured before, to 6.3 ± 0.1 ns, measured after 35 days of experiment. These changes were in agreement with the observed viscosity rise, resulting from formation of polar molecules with propensity to form hydrogen bonds. The viscosity increase reduced the frequency of collisions between the chromophore and its environment,

Fluorescence spectroscopy was applied to monitoring changes in virgin olive oil during storage (Sikorska et al. 2008b). The extra virgin olive oil samples were stored for the period of 12 month in different conditions: in clear and green glass bottles exposed to light, and in darkness. Changes occurring in olive oil during storage were assessed by total fluorescence and synchronous scanning fluorescence spectroscopy techniques. In the total fluorescence spectra the intensity of emissions ascribed to tocopherols and chlorophyll pigments decreased during storage, depending on the storage conditions. Additional bands appeared in oils exposed to light in the intermediate range of excitation and emission wavelengths. Bands attributed to tocopherols, chlorophylls and those tentatively ascribed to phenolic compounds were observed in the synchronous scanning fluorescence spectra, allowing monitoring of the storage effects on these constituents. PCA of the synchronous fluorescence spectra revealed systematic changes in the overall emission characteristics dependent on the

Fig. 8. (a) Scores plot for the two most significant principal components, PC1 vs. PC2, of a PCA

of the synchronous scanning fluorescence (SSF) spectra (λ = 10 nm) of virgin olive oil samples. A nonstored sample (Start), and samples stored in different conditions: in darkness (D), in green glass bottles (DG) and in clear glass bottles (CG). The samples are numbered according to the months of storage. The values in brackets describe the fraction of the total variation explained by each of the PC. Each point represents an average of the spectra obtained from three replicates . (b) One-vector loading plots for the PC1 and PC2 principal components. Reprinted with permission from Sikorska et al., 2008b. Copyright 2008, John Wiley and Sons.

consequently lowering the non-radiative contribution to the luminescence decay.

**3.6 Assessing quality changes of olive oil during storage** 

storage conditions, such as exposure to light, and packaging, Fig. 8.

Fluorescence spectra of olive oils contain information about fluorophores (tocopherols, phenolic compounds, and chlorophylls) that are important for oil quality. The spectra may be used to monitor either selected constituents or to determine overall sample characteristics, which may serve as the spectral fingerprint. The analytic potential of fluorescence is enhanced by application of multivariate data analysis methods for the analysis of spectra.

The review of literature data demonstrates that fluorescence measurements conducted directly on olive oil samples with subsequent multivariate data analysis can be efficiently used for qualitative and quantitative analysis as a valid alternative to conventional, chemical methods of quality assessment. These methods can be used for oil discrimination and for quantitative determination of fluorescent components after an appropriate calibration. Further studies are needed to resolve various issues that are important for practical application of the fluorescence techniques, among which are the method verification for specific kinds of oil and identification and quantification of other fluorescent oil constituents.

### **5. Acknowledgment**

Grant NN312428239, 2010-2013, from the Polish Ministry of Science and Higher Education is gratefully acknowledged.

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**5** 

*Balkesir University* 

*Turkey* 

**Metal Determinations in Olive Oil** 

Sema Bağdat Yaşar, Eda Köse Baran and Mahir Alkan

It is widely known that trace metals have negative effects on the oxidative stability of olive oil. Natural composition of olive fruit, natural contamination from soil, fertilizers, industrial applications or highways near the plantations are the main sources of metals in olive oils. The olive oil may also be contamined with the metals during the production process and contact with storage materials. The level of trace metals in olive oil is one of the quality parameters and also effective on oil oxidation and human health. Oxidation leading to the development of unfavorable odours and taste is one of the major reasons of deterioration of olive oils**.** The factors that most affect the rate of oxidation are the degree of unsaturation, the amount of oxygen, temperature, light and the presence of metals (mainly transition metals such as Fe and Cu) (Meira et al., 2011; Sikwese & Duodu, 2007). The trace metals enhance the rate of oxidation of edible oils by increasing the generation of free radicals from fatty acids or hydroperoxides. Benedet & Shibamoto observed that trace amounts of Fe, Cr, Pb and Cd contribute oxidative effects to lipid peroxidation (Benedet & Shibamoto, 2008). The determination of metals has been a difficult analytical problem because of the hard organic content of the oil matrix. The analytical techniques used for metal determinations in oils are both emission and absorption spectrophotometry. ICP-OES (Allen et al., 1998; Angioni et al., 2006 ; Anthedimis et al., 2005; Costa et al., 2001; De Souza et al., 2005; Murillo et al., 1999; Zeiner et al., 2005), FAAS (Bat & Cesur, 2002; Carbonell et al., 1991; Köse Baran & Bağdat Yaşar, 2010; Nunes et al., 2011), ETA-AAS (Karadjova et al., 1998; Kowalewska et al., 1999 ; Zeiner et al., 2005), GFAAS (Allen et al.,1998 ; Ansari et al., 2009; Calapaj et al., 1988; Chen et al., 1999; Cindric et al., 2007; De Leonardis et al., 2000; Hendrikse et al., 1988, 1991; Lacoste et al., 1999; Martin-Polvillo et al., 1994 ; Matos Reyes & Campos, 2006; Mendil et al., 2009; Nash et al., 1983; Van Dalen, 1996), and ICP-MS (Benincasa et al., 2007 ; Bettinelli et al., 1995; Llorent-Martinez et al., 2011a, 2011b; Pereira et al., 2010; Wondimu et al., 2000) are the most commonly used techniques for the determination of metal contents in oils

In this chapter, recent determination techniques and sample pretreatment methods have been described and compared with each other. Additionally, a novel metal extraction procedure has been introduced in detail. In recent years, scientists have been interested in defining the bioavailable amount of metals more than total metal concentration. Taking into account this, fractionation and speciation analysis of metals in oil samples have also been

**1. Introduction** 

(Duyck et al., 2007).

discussed in the chapter.

