Special extraction technique indicates irradiation levels for cashew nuts

Food irradiation is approved for use in over 60 countries for various applications and purposes in a wide variety of foodstuffs, mostly as a post-harvest phytosanitary measure.

The European Standard EN 1785:2003 allowed the detection of irradiated cashew nut at an irradiation dose of 700 Gy; however, for nutmeg neither 2-DCB nor 2-TCB could be detected at an irradiation dose of 1000 Gy. For the further improvement of the sensitivity to detect irradiation a novel method of analysis was developed, in-house validated and applied to several cashew nut and nutmeg samples. A combination of matrix solid phase dispersion, conversion to oxime derivatives, and measurement with HPLC–HRMS delivered detection limits of smaller than 10 μg/kg for 2-DCB and 2-TCB. Irradiation at doses of less than 100 Gy (cashew nuts) and 400 Gy (nutmeg) could be detected. Twenty-six cashew nut and 14 nutmeg samples obtained from retailers in 10 different EU Member States tested negative for 2-ACBs using the optimized HPLC–HRMS method. Consequently, there is no reason to believe that 2-ACBs are not unique indicators of treatment with ionizing radiation.

The irradiation of certain foods and food ingredients is regulated in the EU by Directive 1999/2/EC (European Communities, 1999a). The Community list of foodstuffs which may be treated with ionizing radiation to the exclusion of all others and the maximum radiation doses authorized are given in Directive 1999/3/EC (European Communities, 1999b). The only harmonized entry at EU level is for dried aromatic herbs, spices and vegetable seasonings at a maximum overall average absorbed radiation dose of 10 kGy. However, authorisations at the level of EU Member States exist for a wider variety of foods (European Union, 2009).

Proper labeling of irradiated food products and ingredients is required at EU level as well as by the FAO/WHO Codex Alimentarius (Codex Alimentarius, 2003). For checking compliance with legislation a number of analytical methods have been elaborated and standardized by the European Committee for Standardization (CEN). Among this suite of methods is EN 1785:2003 Foodstuffs – Detection of irradiated food containing fat – Gas chromatographic/mass spectrometric analysis of 2-alkylcyclobutanones (European Committee for Standardization, 2003). The standard specifies a method for the identification of irradiation treatment of food containing fat. It is based on the mass spectrometric (MS) detection of radiation-induced 2-alkylcyclobutanones (2-ACBs) after gas chromatographic (GC) separation. The method has been successfully tested in interlaboratory trials on raw chicken, pork, liquid whole egg, salmon and Camembert. Other studies demonstrate that the method is applicable to a wide range of foodstuffs, although for mangoes, a small number of false positives were reported. However, these were attributed to analytical difficulties encountered as 2-ACBs have never been detected in non-irradiated samples of this product.

A study by Variyar, Chatterjee, Sajilata, Singhal, and Sharma (2008) claimed the natural occurrence of 2-ACBs in cashew nut (Anacardium occidentale) and nutmeg (Myristica fragrans), thus disproving the hypothesis that 2-ACBs are radiolytic degradation products of fat which can serve as unique markers for irradiation treatment of fatty foods. The authors postulated that a special extraction technique, i.e. supercritical fluid extraction (SFE) using carbon dioxide, in combination with clean-up of the extract using thin-layer chromatography allowed them to identify traces of 2-ACBs in the mentioned food products. For nutmeg those findings have not been confirmed by another independent study, although a similar analytical approach (SFE with SPE clean-up) was applied (Chen et al., 2012). Meanwhile, other reports came out supporting the fact that 2-ACBs do not occur naturally (Leung et al., 2013 and Driffield et al., 2014). The latter reports did not use EN 1785 for the determination of 2-ACBs but claimed that their analytical methodology is superior or at least equivalent.

The methodology used in EN 1785:2003 has been developed and validated in the 1990s (Raffi et al., 1994). Since then enormous progress has been made in analytical technologies and instrumentation, allowing miniaturization of solvent volumes and improvements in sensitivity for the analysis of 2-ACBs (reviewed by Crews, Driffield, and Thomas (2012)). For example, proposals have been made to replace Soxhlet extraction by pressurised liquid extraction (PLE) to isolate total fat (Obana, Furuta, & Tanaka, 2005), to apply a direct extraction method using acetonitrile (Hijaz, Kumar, & Smith, 2010), to use gel-permeation chromatography instead of Florisil for clean-up and GC–MS/MS instead of GC–MS (Takahashi, Ishii, & Matsumoto, 2013), or replacing GC–MS by LC–MS/MS (Leung et al., 2013 and Driffield et al., 2014). Next to these methods of analysis using mass spectrometric detection approaches based on ELISA (Zhao, Wang, Li, & Ha, 2013) and biosensors (Zhao, Ha, Yue, & Wang, 2015) also exist.

Triggered by the report that 2-ACBs might not be unique indicators of irradiation we compared the merits of several novel approaches for the analysis of 2-ACBs in cashew nuts and nutmeg using the performance of EN 1785:2003 as benchmark. In addition, cashew nut and nutmeg samples purchased in different EU Member States were assessed to verify the assumption that 2-ACBs do not occur in non-irradiated foods.

source: ascience Direct