Olive Oil Traceability Studies Using Inorganic and Isotopic Signatures: A Review

Overview

This review summarizes developments in inorganic and isotopic analysis for geographical authentication of olive oil. It compiles reported trace element concentrations from the literature (Figure 3; Table 1), discusses sample preparation techniques (microwave-assisted digestion, acid extraction, emulsification, chelation, dilution with organic solvent, solubilization with alkaline reagent), detection techniques (ICP-MS, ICP-OES, GFAAS, FAAS), method validation challenges (absence of a certified reference material for olive oil), factors that modify the elemental profile (agro-climatic conditions, extraction process, storage), and isotopic approaches (stable isotopes of C, H, O; strontium isotope ratios).

This is a review; it reports no new analytical data. Values cited in this review should be traced to the underlying primary studies.

Key numbers

Compiled concentration ranges (Figure 3, p. 6; Section 2.1, pp. 6-7; µg/kg):

Elements classified into three concentration categories:

1. Low (well below 1 µg/kg median): Rb, lead (Pb).
2. Medium (medians between 10 and 100 µg/kg): arsenic (As), Ba, Mn, nickel (Ni), Sr.
3. High (100 to 10,000 µg/kg): Ca, chromium (Cr), Fe.

“They can be classified into three categories, with (1) Rb and Pb well below 1 µg/kg; (2) elements such as As, B, Mn, Ni, and Sr ranging on average between 10 and 100 µg/kg; and (3) elements including Cr, Fe, and Ca ranging between 100 to 10,000 µg/kg” (p. 1 abstract).

Literature ranges cited for specific elements (Section 2.1, pp. 6-7):

Co: 1.0 to 5450 µg/kg [ref 48]. Mg: 56 to 1030 µg/kg [ref 36]. Mn: 3.5 to 150 µg/kg [ref 51]. Cr: 12 to 1830 µg/kg [ref 52].

Analytical methods compilation (Table 1, pp. 10-11):

ICP-MS used in approximately 68% of published studies (Figure 5, p. 14). Sample sizes in compiled studies range from 5 to 539. Recoveries reported where available: 66% to 120% across studies. Several studies report no LOD or CRM.

Factors affecting olive oil elemental composition (Section 2.3, pp. 16-17):

Agro-climatic conditions (Section 2.3.1, p. 16): “It has been demonstrated that several parameters such as the olive cultivar [63], irrigation of olive trees [30], use of fertilisers [77], or fluctuations in annual climatic parameters [78] may modify the elemental profile of olive oil.”

Extraction process (Section 2.3.2, p. 16-17): “During the oil extraction process, olives are in direct contact with metallic surfaces that can generate contamination in the final product.” Addition of water during extraction increased Sc, Cr, Fe, Co, and Ni concentrations. Use of water in industrial-scale refining decreased Ca. Filtration (removal of pomace residues and leftover water) “can significantly alter the trace element content of both olive oil and pomace residues” [ref 81]. Non-centrifuged-to-centrifuged ratios showed “discrepancies of up to three orders of magnitude” for some elements [ref 18]. Storage and transport conditions, including container type (polypropylene suggested for Cu and Fe), can also affect composition.

CRM limitations (Section 2.2.3, p. 15):

“Thus far, there is still no certified reference material (CRM) for trace elements in olive oil despite of its growing worldwide consumption.” NIST SRM 2387 (peanut butter) is the closest natural edible lipid matrix CRM. Engine oil CRMs (S23-100Y from SPEX CertiPrep, EnviroMAT HU-1) have been used but are not matrix-matched.

Evidence Fitness

EF-4 (context only). This is a review that compiles literature data and discusses methodology, factors affecting composition, and analytical challenges. It provides no new measurements. Values cited should be attributed to the underlying primary studies. It supports contextual understanding of what modifies trace element levels in olive oil (cultivar, irrigation, fertilizers, extraction equipment, centrifugation, filtration, storage containers) and the state of analytical methodology.

Methods

Not applicable (review article). The review surveys studies published through early 2022 on inorganic and isotopic analysis of olive oil for geographical authentication.

LOD/LOQ: Not applicable (review).

CRM/Recovery: Not applicable (review).

Limitations: Compilation study; no original data. The review notes that some compiled studies report LODs that “seem atypically high” and may reflect contamination during sample preparation (p. 15). One-third of studies reviewed did not report LOD information (p. 14-15).

Implications

Certification: Provides a comprehensive overview of the factors known to alter trace element concentrations in olive oil, including those relevant to HMT&C: extraction equipment (stainless steel contact increases Fe, Cr), centrifugation and filtration (can alter concentrations by orders of magnitude), water addition during processing, and container type. These are actionable supply-chain considerations.

Courses: Section 2.3 on factors affecting composition (cultivar, irrigation, fertilizers, extraction surfaces, centrifugation, filtration, storage) and Figure 4 summarizing analytical approaches provide a structured overview for teaching olive oil trace element variability.

Provenance notes

Open access (CC BY 4.0). MDPI journal (Molecules), DOAJ listed. Two authors (Nasr and Donard) overlap with Nasr et al. 2021. Deposit: HMI-MIT-olive-oil. No conflicts of interest declared. Funded by European Project TunTwin (Horizon 2020, Grant No. 952306).

Related evidence

• Olive Oil (Section 1: processing; Section 2: mitigation and inputs)

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