**Metal Determinations in Olive Oil**

Sema Bağdat Yaşar, Eda Köse Baran and Mahir Alkan *Balkesir University Turkey* 

#### **1. Introduction**

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

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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 (Duyck et al., 2007).

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 discussed in the chapter.

Metal Determinations in Olive Oil 91

**Microvawe digestion procedure Reagent Metals determined Reference** 

Mg, Ca, Cr, Fe, Mn, Cu, Ni, Zn, Cd, Pb

Fe, Mn, Zn, Cu, Pb, Co, Cd, Na, K, Ca, Mg

Ca, Fe, K, Mg, Na, Zn, Al, Co, Cu, Mn, Ni,

Ag, As, Ba, Be, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Sb,

HNO3–H2O2 Cd, Cu, Pb, Zn Angioni et al.,

HNO3–H2O2 Cu, Fe, Ni, Zn Nunes et al.,

Be, Mg, Ca, Sc, Cr, Mn, Fe, Co, Ni, As, Se, Sr, Y, Cd, Sb, Sm, Eu,

Cr, Pb

Ti, Tl, V

Gd

Bağdat Yaşar & Güçer, 2004

Mendil et al.,

Cindric et al.,

2009

2007

2006

2011

Benincasa et al., 2007

Llorent-Martinez et al., 2011a, 2011b

HNO3

HNO3–H2O2

HNO3–H2O2

HNO3

HNO3

extraction with special agents (Köse Baran & Bağdat Yaşar, 2010).

Table 1. The summary of microwave digestion procedures for various metals in olive oil.

Sample preparation involves acid extraction (Anwar et al., 2004; De Leonardis et al., 2000; Dugo et al., 2004; Jacob & Klevay, 1975), solid phase extraction (SPE) (Bat & Cesur, 2002) or

After the extraction of metals from oil with nitric acid, hydrochloric acid or acid mixture, the extracts are analyzed. Despite the fact that extraction method has the same advantage both in the separation and preconcentration of metals in oil samples, the recoveries are not satisfactory for many metals in most cases. Bat and Cesur described another method for the preconcentration and separation of copper in edible oils, based on using a solid Pbpiperazine-dithiocarbamate complex for extraction and a potassium cyanide solution for

Anwar et al. reported a simple acid-extraction method for the determination of trace metals in oils and fats. The method has been performed with the use of ultrasonic intensification and successfully applied for accurate determination of iron, copper, nickel and zinc in oils (Anwar et al., 2004). Many extraction procedures are available in literature, the summary of

130 oC 10 min. 140 psi, 150 oC 10 min. 200 psi, 10 min. cooling, 160 oC

2 min. for 250 W, 2 min. for 0 W, 6 min. for 250 W, 5 min. for 400 W, 8 min. for 550 W, vent.: 8 min.

250 W 2 min., 0 W 1 min., 250 W 2 min., 600 W 1 min., 400 W 5 min.,

25i-90f oC 5 min. 700 W, 90i-90f oC 3 min. 600 W, 90i-170f oC 10 min. 600 W, 170i-170f oC 7 min. 600 W

300 W (83%) for 15 min., 600 W (75%) for 10 min., 1200 W (65%) for 15 min., 300 W (83%) for 5 min.

750 W 90 oC 6 min., 750 W 90 oC 4 min., 1000 W 180 oC 8 min., 1000 W 180 oC 15 min. (35 bar), vent.: 20 min

250 W, 4 min., 0 W 4 min., 250 W 5 min., 400 W 7 min., 700 W 6 min.,

back extraction (Bat & Cesur, 2002).

these is given in Table 2.

20 min. 200 psi

vent.: 3min.

350 W 5 min.

i: initial ; f: final

**2.3 Extraction** 
