Naturally occurring nanoparticles in food Michael Armin Rogers Food nanotechnology is extremely complex and with hesitant consumers this may be sufficient to impede this technology from being implemented and benefits realized. Nano-sized particles are not new to our food supply and there are numerous naturally occurring nano-sized elements present in the foods we consume, including foods as wholesome as milk. Furthermore, nanoparticles arise as a result of processing, such as homogenization and milling and in complex foods, there also exists the possibility that certain combinations of ingredient spontaneously self-assemble into nano-fibers and micelles. During digestion, nanofabrication is used to aid in transport of lipids due to the micellization of fatty acids and monoglycerides with bile salts, phospholipids, and cholesterol. It is imperative to advance the science of nanomaterials with the technology, and to be intimately aware that our biology is not experiencing for the first time nanomaterials. Address Department of Food Science, University of Guelph, Guelph, Ontario N1G2W1, Canada Corresponding author: Rogers, Michael Armin (mroger09@uoguelph.ca) Current Opinion in Food Science 2015, 7:14–19 This review comes from a themed issue on Food Chemistry & Biochemistry Edited by Alejandro G Marangoni http://dx.doi.org/10.1016/j.cofs.2015.08.005 2214-7993/Published by Elsevier Ltd. Introduction Food nanotechnology, throughout the past decade, has become a remarkably active space for research encoun- tering exponential growth in publications per year, rising 10-fold between 2004 and 2014. Throughout this period, in excess of 3800 peer-reviewed manuscripts have been published and indexed via Web of Science (Figure 1). This has, in part, resulted in media outlets sensationaliz- ing the potential adverse health effects, and as a result increased negative consumer perception of food nano- technology and the food industry on a whole. Albeit, there may be associated risks with some nanomaterials in our food supply [1  ], by no means are these risks universal, as naturally occurring nanomaterials have been consumed since Neolithic times [2  ]. As well, since the industrial revolution, coinciding with the advent of modern food preservation, incidentally added nanomaterials, a by- product of these techniques, has led to the creation of a subset of colloids falling within the nanoscale [3  ]. Intriguingly, consumer perception shows that the impor- tance of ‘naturalness’ in food products is significant factor influencing the perceived risk and the perceived benefit of nanotechnology foods [4]. Other prohibitive factor includes uncertainties in the level of awareness and attitudes toward the use of nanotechnology by the indus- try and the existence scientific gaps in knowledge [5]. Two approaches to nanotechnology are commonly used in the food industry and include a ‘bottom-up’ or ‘top- down’ approach. The ‘top-down’ approach is accom- plished via a reduction in particle size during physical processing, such as homogenization or milling. Converse- ly, the ‘bottom-up’ approach utilizes the ability of mole- cules to self-assemble. Self-assembly occurs on the nanometer scale and can be achieved via a balance of contrasting non-covalent interactions [6  ]. Examples in- clude, the organization of the casein micelle and folding of globular proteins [7]. These nano-foods, albeit still in their infancy, have tre- mendous potential to increase the safety of foods, create healthier more nutritious foods, enhance flavor or mask undesirable flavors [8]. Current application of nanotech- nology in foods may allow the detection of foodborne pathogens, via nanosensors [9] or enhanced delivery of nutraceuticals with low bioaccessibility and bioavailabili- ty [10]. Most nanoparticles used are classified as colloids (i.e., emulsions, micelles, mono-layer and bi-layer) [11]. When materials are modified and the colloids be- come submicron, the nanoparticles have vastly modified chemical and physical properties and may interact differ- ently with the living systems thereby causing unexpected toxicity [12]. Naturally occurring nanomaterials in milk — emulsions, micelles, fibers, and foams Nature has a remarkable ability to generate nanoscale elements on the basis of the principles of self-assembly. As such, many natural organic foods contain nanomater- ials that have been consumed safely for generations [13]. To illustrate, milk has one of the most functional nanomaterials — the casein micelle. The size of the casein micelle (Figure 2) is typically between 100 and 200 nm, and may be considered, using the coat-core model, as a hard sphere, comprised of proteins stabilized by the presence of calcium phosphate, coated in a hairy layer containing k-casein [14,15]. The nano-assemblies of Available online at www.sciencedirect.com ScienceDirect Current Opinion in Food Science 2016, 7:14–19 www.sciencedirect.com