Nanoparticles

Application of nanoparticles — particles with one or more dimensions at the nanoscale — in food, medicine and agricultural products is booming and many nanobased products are already on the market [40]. Inherent to their size and surface-to-volume ratio nanoparticles often show a high chemical reactivity. The quantum-size and Coulomb-charging effects of nanoparticles may yield particles with exceptionally electric conductivity or resistance, high capacity for storing or transferring heat or changed solubility properties. Within food technology nanoparticles are used in food conservation, dietary supplements, food additives, packaging materials, functional foods and intelligent food. Some typical examples of application in the food area can be found: bakeries in Western Australia have incorporated nanocapsules containing omega-3 fatty acids in bread, the capsules will open only in the acidic environment of the stomach; the company NutraLease™ utilizes micelles with a diameter of 30 nm to deliver lycopenes, beta-carotene, lutein, phytosterols, CoQ10 and omega-3 fatty acids; Unilever is developing low fat ice creams by decreasing the size of the emulsion particles and The Oilfresh Corporation marketed a new nanoceramic product that prevents the oxidation and agglomeration of fats in deep fryers. It is envisaged that within agricultural practices nanoparticles can be used for precision farming, meaning that autonomous nanosensors are applied for realtime monitoring and early warning of plant health issues, and for controlled release of pesticides and herbicides encapsulated in nanomicelles. Some of these developments already come into reality are: Syngenta is using nanoemulsions in its pesticide products and also marketing the microencapsulated product Gutbuster® that releases its content in the alkaline environment of the insect stomach; and a growth-promoting product PrimoMaxx® is used to strengthen the physical structure of turfgrass. The unique properties of nanoparticles make them attractive in the applications mentioned previously but also impose new unforeseen risks, hence making an evaluation of the appropriateness of the current risk assessment protocols and methods necessary. The appropriateness of risk assessment methodologies currently in place to deal with the new properties of the nanoparticles is being addressed by different authorities. Current methods for the identification of nanoparticle hazards are probably adequate but the methods for characterization of the hazard (i.e., establishment of toxicological dose-response relationships) and subsequent exposure assessment need to be adapted. Improvement of current assessment methodology should consider the following aspects: (i) physical parameters such as particle size, size distribution, surface charge, (ii) agglomeration and disagglomeration properties in different environments, (iii) impurities within, and adsorbed species onto the surface and (iv) biological processes involving nanoparticles, including translocation, cellular uptake and toxicological mechanisms.

The analytical challenge for the required monitoring of nanoparticles in the food chain is immense. A vast array of analytical techniques is typically used for the characterization of the physical properties of manufactured nanoparticles: the mean size and its distribution is measured by techniques like photon correlation spectroscopy (PCS), laser diffractometry (LD), light scattering (LS), differential mobility analysis, TOFMS and microscopy, while electrophoresis is typically used to determine the particle charge density [41,42]. The crystalline structure of a nanosuspension can be assessed by differential scanning calorimetry (DSC) [41], polarized optical microscopy and scanning electron microscopy [43]. Electron spectroscopy for chemical analysis (ESCA), X-ray photoelectron spectroscopy (XPS), secondary ions mass spectroscopy (SIMS) and matrix assisted laser desorption ionization MALDI TOFMS are used for surface structure and chemical composition analysis of nanoparticles [42]. It should be stressed that so far the key issue of isolation and sample preparation of nanoparticles from food or feed samples has been hardly addressed. Definitely it will be very difficult to maintain the integrity of the nanoparticle during sample preparation and the subsequent analysis. Apart from that, many of the characterization tools employed and cited previously will not be easily implemented within a routine food control environment.

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