A new green extraction/clean up method based on Natural Deep Eutectic Solvents (NADESs) for bisphenols and alkylphenols in foodstuffs

Food manufacturing comprises several production phases from the cultivation in field to the packaging. In every single step of the production the food may be unintentionally contaminated by chemical substances that are called contaminants (Cs) [1]. The Cs that have appeared only recently or that are gaining concern because of their negative effects on humans are called “Emerging Contaminants (ECs)” [2]. Bisphenols (BPs), alkylphenols (APs), some pesticides, and other substances, such as perfluoroalkyl substances (PFAS), have been classified as ECs [2]. BPs are plasticisers added to food packaging to increase its flexibility, workability, and extensibility. Bisphenol A (BPA) had been the most used BPs in packaging production until its endocrine disruptor effects was declared [3]. The European Commission, taken into account the hazard of ECs on human health, has set specific migration limits (SMLs) and maximum residue limits (MRLs) for these substances in foodstuffs. For instance, SMLs of 0.05 mg·kg-1 and 9 mg·kg-1 have been established for BPA [4] and bisphenol A diglycidyl ether (BPADGE) [5], respectively. At the moment, no limitation is reported for bisphenol AF (BPAF), bisphenol B (BPB), bisphenol E (BPE), bisphenol F (BPF) and 4-nonylphenol (4-NP) in materials and articles intended to come into contact with food. Extraction/clean-up approaches for BPs [6-9] and APs [10] in foodstuffs are typically based on conventional solid-phase extraction (SPE) or QuEChERS coupled with SPE purification steps. However, these methods require a large use of organic solvents and extensive time-consuming operations. An interesting alternative is represented by the extraction/clean-up based on deep eutectic solvents that were typically used for natural compounds (e.g. polyphenols) and Cs (e.g. PAHs) [11]. Therefore, the aim of these work was to develop a new natural deep eutectic solvent (NADES) based extraction approach for the analysis of BPs and APs (i.e. BPA, BPAF, BPB, BPE, BPF, 4-NP, BPADGE) in foodstuffs. Real samples, namely raw ham, tuna in glass jar, dried tomatoes, dried apples and dried blueberries, have been collected from the local markets. The NADESs used as extractants (polar and apolar) have been synthesized by mixing glucose with choline chloride (polar NADES), and menthol with camphor (apolar NADES) in proper ratios. The extraction/clean-up method consisted of a simple mixing of specific amounts of NADES with the homogenized real sample in a centrifuge tube and a successive treatment in a heated ultrasound system at 60°C for twenty minutes. Finally, the mixture was centrifuged and the supernatant (NADES phase) was collected, diluted and filtered before a direct analysis by HPLC-FLD. Some important variables affecting both the synthesis of NADESs and the extraction/clean-up method have been investigated. In NADES synthesis the amount of compounds and water used in the preparation, the manual mixing step in a mortar, and the synthesis conditions including stirring and heating have been studied. In the application of the extraction/clean-up method to real samples, the following aspects have been evaluated in terms of clean-up efficiency, recovery of BPs and alkylphenols, and external interferences: polar and apolar characteristics of NADES, handling of viscous NADES during operations, selection of proper lab equipments (e.g. centrifuge tubes), solvent and filter selection used for dilution and filtration. The preliminary results obtained by the proposed extraction/clean-up method based on NADESs have demonstrated that clean extracts and very good recoveries can be achieved for all the real matrices investigated.