Abstract
Due to food complexity and the low amount at which contaminants are usually present in food, their analytical determination can be particularly challenging. Conventional sample preparation methods making use of large solvent volumes and involving intensive sample manipulation can lead to sample contamination or losses of analytes. To overcome the disadvantages of conventional sample preparation, many researchers put their efforts toward the development of rapid and environmental-friendly methods, minimizing solvent consumption. In this context, microwave-assisted-extraction (MAE) has obtained, over the last years, increasing attention from analytical chemists and it has been successfully utilized for the extraction of various contaminants from different foods. In the first part of this review, an updated overview of the microwave-based extraction technique used for rapid and efficient extraction of organic contaminants from food is given. The principle of the technique, a description of available instrumentation, optimization of parameters affecting the extraction yield, as well as integrated techniques for further purification/enrichment prior to the analytical determination, are illustrated. In the second part of the review, the latest applications concerning the use of microwave energy for the determination of hydrocarbon contaminants—namely polycyclic aromatic hydrocarbons (PAHs) and mineral oil hydrocarbons (MOH)—are reported and critically overviewed and future trends are delineated.
Highlights
The first application of microwave energy dates back to 1986, when Ganzler et al [1], investigated the applicability of microwave irradiation to the extraction of various types of compounds from soil, seeds, foods and feeds, prior to chromatographic determination
Different from traditional heating sources, which require some time to heat the core of the sample, microwaves act on the whole sample volume or on localized heating centres constituted by polar molecules contained in the product, allowing for rapid heating, maintaining the temperature gradient low
When the presence of water in the sample has a negative impact on the extraction yields and/or reproducibility, the sample needs to be dehydrated or lyophilized or the water content has to be standardized in order to obtain uniform heating
Summary
The first application of microwave energy dates back to 1986, when Ganzler et al [1], investigated the applicability of microwave irradiation to the extraction of various types of compounds from soil, seeds, foods and feeds, prior to chromatographic determination. Concerning organic contaminants, microwave-based techniques have been successfully applied to pesticides, polychlorinated biphenyls, N-nitrosamines, mycotoxins, residues of veterinary drugs and last but not least, hydrocarbon contaminants The latter comprise well known food contaminants such as polycyclic aromatic hydrocarbons (PAHs), as well as emerging contaminants such as mineral oil hydrocarbons (MOH), which have attracted great attention in the last decade. The analytical determination of both PAHs and MOH must be preceded by an extraction step, whose importance is often underestimated and which should guarantee quantitative recovery with minimal solvent consumption [2] In this context, extraction carried out with traditional methods (Soxhlet extraction, liquid-liquid or solid-liquid extraction, traditional saponification, etc.) involves large volumes of solvent and intensive sample manipulation, it is time consuming and can lead to contamination during sample preparation and poor reproducibility. With some exceptions for older significant works, scientific papers published over the last 10 years were considered for this review (Web of Science, Scopus, Pubmed, until 30 August 2019)
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