Differential scanning calorimetry: A potential tool for discrimination of olive oil commercial categories
Introduction
Commercial categories of olive and olive-pomace oils have been initially classified in 1966 and were reclassified in 2001, by the European Community (EC) Council of Regulation in an attempt to avoid misleading of consumers and operators and to preserve the image of high-quality products as extra virgin and virgin olive oils [1].
Extra virgin olive oil (EvOo) (free acidity <0.8 g 100 g−1) is the highest quality product among olive oils as it is obtained from olive fruits using only mechanical processing steps or other physical means under conditions that do not lead to oil alteration [1]. Refining treatment can be applied to virgin olive oil of low quality to obtain products classified as refined virgin olive oil (ROo) (free acidity <0.3 g 100 g−1). Some mixtures of oils of different commercial categories are also legally permitted and are commonly performed by producers, who assess several chemical parameters (i.e. free acidity, peroxide value, fatty acid and sterols composition, etc.) of the oils to get a product that meets compositional Legal Limits set by the EU [2]. In particular, olive oil (Oo) (free acidity <1.0 g 100 g−1) can be produced by blending virgin olive oil with ROo.
Among olive-pomace oils, refined crude olive-pomace oil (RPo) (free acidity <0.3 g 100 g−1) is produced by refining crude olive-pomace oil previously obtained from pomace by means of solvent extraction, and olive-pomace oil (Po) (free acidity <1.0 g 100 g−1) is made by blending RPo and virgin olive oil.
The EC Council of Regulation has recently redefined the physico-chemical characteristics of olive and olive-pomace oils in an attempt to harmonize them with the international standards set by the International Olive Oil Council and the Codex Alimentarius [2], [3]. Major differences between EvOo, Oo and Po compositions are linked to minor compound content: for example only EvOo contains a significant presence of phenolic compounds. On the other hand, Po has higher amount of waxes (≤250 mg kg−1 for EvOo, ≤350 mg kg−1 for Oo and >350 mg kg−1 for Po from EC Reg. no. 702/2007) and total aliphatic alcohols (erythrodiol and uvaol) (≤4.5% for EvOo and Oo, >4.5% for Po from EC Reg. no. 702/2007) that were more efficiently extracted from fruit husk by organic solvents.
The olive oil classification is generally carried out with physico-chemical and sensory methods, but wrong classifications can still occur. Chemical methods are most commonly applied for this scope, but they are known to be expensive, time-consuming, and to have high environmental impact. Sensory evaluation is a powerful tool, but it is necessary a continuous training of the panel to achieve reliable oil assessments; furthermore, the correlations between sensory attributes and chemical composition have not been fully clarified yet [4]. Availability of new/additional analytical techniques as supporting tools for currently used methods may be helpful to improve olive oil classification and market management.
Differential scanning calorimetry (DSC) is an analytical technique that has been applied in oil and fat research for the characterization of oils from different vegetables sources, providing a reproducible method for their identification [5], [6] as thermal properties were found to be related to the chemical composition in extra virgin olive oils [7]. Jiménez Márquez and Beltrán Maza [8] were able to differentiate monovarietal virgin olive oils based on temperature (onset and transition range) of crystallization and melting profiles, which were well correlated with oleic and linoleic acid contents. More recently, a good relation was reported between thermal properties and major (triacylglycerols and fatty acids) and minor components (free fatty acids, diacylglycerols, and primary and secondary oxidation products) of monovarietal extra virgin olive oils for both cooling and heating profiles that were deconvoluted into the constituent peaks and related to specific triacylglycerol (TAG) species [9], [10]. DSC application upon cooling and heating also appeared very promising in discriminating among oil samples from olives of different cultivars and/or harvesting periods [9], [10].
Little information is reported in literature about DSC characterization of olive oils of different commercial categories. Jiménez Márquez associated the melting thermograms of virgin, refined, and lampante olive oils to TAG composition [11]; melting enthalpy and/or transition temperature were found to be related to the different content of TAG fractions in these oils. Angiuli et al. reported that calorimetric techniques (DSC in particular) may be used to efficiently discriminate between commercial and guaranteed origin extra virgin olive oils [12], as well as for the recognition of the physical and/or mechanical treatments (refining, deodorization, filtration, etc.) in virgin olive oil [13]. However, chemical composition of the oils was not considered in these studies [12], [13].
The aim of this preliminary work was to verify the potential DSC application to discriminate among olive oils of different commercial categories, evaluating the relationship between thermal properties (obtained upon cooling and heating) and chemical composition (major and minor components). Deconvolution analysis was applied to better characterize the complex nature of the transitions.
Section snippets
Sampling
All commercial olive oil samples were supplied by Coppini Arte Olearia (Parma, Italy) and stored in dark bottles without headspace at room temperature before analysis. The olives used for oil production were hand-picked in 2006 and belonged to two cultivars (Nocellara del Belice and Ogliarola Messinese) from Trapani (Sicily, Italy). Olives were processed by a continuous industrial plant with a working capacity of 1 ton h−1 equipped with a hammer crusher, a horizontal malaxator (at a temperature
Chemical composition
Chemical composition and oxidation parameters of EvOo, Oo, ROo, Po and RPo, obtained as described in Section 2, are reported in Table 1. Sixteen TAG were identified in all samples; eight of them were separately quantified and the others were quantified as pairs (LLL + LLPo, OLL + OLPo, LLP + OLnO and OLP + OOPo).
OLL + OLPo, OLO, OLP + OOPo, OOO and SLO accounted for more than 85% of the total TAG in all commercial categories, whereas SOP was present in the lowest percentage (Table 1). Comparing olive and
Conclusions
The results of this preliminary investigation confirmed that both cooling and heating thermograms may be a useful tool to discriminate among olive oil categories, as the oils developed different crystallization and melting profiles. Application of deconvolution analysis to DSC thermograms can provide additional information for olive oil classification and for a better understanding of the relationship among chemical composition (major and minor components) and thermal properties.
The evaluation
Acknowledgments
The authors would like to thank Stefano Savioli and Mara Mandrioli (University of Bologna) for their technical support and assistance during sample analysis.
References (32)
- et al.
Termochim. Acta
(2007) - et al.
Food Chem.
(2008) - et al.
J. Chromatogr. A
(2005) - et al.
Food Chem.
(2007) - et al.
J. Food Prot.
(2006) - European Community, Commission Regulation 1513/2001 of 23 July 2001 amending Regulations No. 136/66/EEC and (EC) No....
- European Community, Commission Regulation 1989/2003 of 6 November 2003 amending Regulation No. 2568/91/EEC, Off. J....
- European Community, Commission Regulation 702/2007 of 21 June 2007 amending Commission Regulation No. 2568/91/EEC, Off....
- et al.
J. Am. Oil Chem. Soc.
(1996) - et al.
Phytochem. Anal.
(2002)
Phytochem. Anal.
J. Am. Oil Chem. Soc.
Grasas Aceites
J. Agric. Food Chem.
J. Agric. Food Chem.
Ciencia y Tecnologia Alimentaria
Cited by (62)
DSC of Low Molecular Mass Organic Materials and Pharmaceuticals
2023, Handbook of Differential Scanning Calorimetry: Techniques, Instrumentation, Inorganic, Organic and Pharmaceutical SubstancesAnalytical Chemistry and Foodomics: Determination of Authenticity and Adulteration of Extra Virgin Oil as Case Study
2020, Comprehensive FoodomicsCalorimetric analysis points out the physical-chemistry of organic olive oils and reveals the geographical origin
2017, Physica A: Statistical Mechanics and its ApplicationsHigh sensitive and efficient detection of edible oils adulterated with used frying oil by electron spin resonance
2017, Food ControlCitation Excerpt :Many detection methods have been applied to assess the adulteration of qualified vegetable oils based on the physical properties or chemical components of qualified vegetable oils. There are lots of methods, including dielectric spectroscopy (Cataldo, Piuzzi, Cannazza, Benedetto, & Tarricone, 2010; Hu, Toyoda, & Ihara, 2010), nuclear magnet resonance (Agiomyrgianaki, Petrakis, & Dais, 2010; Zhang, Saleh, & Shen, 2013), high performance liquid chromatography (Cunha & Oliveira, 2006), gas chromatography (Hajimahmoodi et al., 2005), mass spectrometry (Lerma-García, Herrero-Martínez, Ramis-Ramos, & Simó-Alfonso, 2008), near infrared spectroscopy (Downey, Mcintyre, & Davies, 2002; Zhang, Cheng, Sun, Hu, Shen, & Wu, 2012), differential scanning calorimetry (Chiavaro et al., 2008), etc. However, all these methods are labor intensive, time-consuming sample preparation and some high toxic chemical reagent for laboratory stuff.