Nanoproteins in food — good, bad or irrelevant?

The debate concerning nanotechnology has echoed that of genetically engineered organisms and their introduction into the environment and the food chain. 

According to Protein nanostructures in food – Should we be worried? ( J.K. Raynes et al. 2014),  a synopsis of a number of scientific studies from both Australia and overseas, while nanotechnology in the food industry is in its infancy, it has the capability to introduce changes at all levels of food production, including nano-based food materials, active packaging, new delivery mechanisms for nutrients and agrochemicals, biosensors for food safety and many other potential applications.

The cat may well be out of the bag though, with a recent story in the Sydney Morning Herald that quoted a privately funded test commisioned by environment group Friends of the Earth that found that nanotechnology was indeed prevalent in a number of common groceries.

A range of foodstuffs – from lollies, sauces and dressings were found to contain nanotechnology that Australia’s food regulator long denied was being used in Australia’s food supply, said the story. It added that, for many years, Food Standards Australia and New Zealand (FSANZ) has claimed there is “little evidence” of nanotechnology in food because no company had applied for approval, and therefore it has not tested for nor regulated the use of nanoparticles.

However, the most commonly researched use of nanotechnology in foods is for active packaging, where the use of nanocomponents can improve barrier resistance, incorporation of active ingredients, and add bio-sensing capability. Nanoemulsions to solubilise and improve the bioavailability of nutrients are also attracting interest.

Over the past ten years, noted the report, there has been an upsurge in food nanotechnology research, including research on food proteins, with a significant increase in the number of peer- reviewed research articles published on this topic. The increase of research in food nanotechnology has raised concerns about the safety of nanotechnology not only in the food industry but also in all products for consumption and use by humans.
 

Protein nanostructures are natural in many foods
The three main components of food: proteins, carbohydrates and lipids, all exist at the nanoscale and come together to form a complex colloidal mixture with diverse physical and chemical properties. The casein micelle in milk provides a good example of this complexity. In bovine milk, the micelle is comprised of four casein proteins (aS1, aS2, b and k) arranged in a large, heterogeneous, dynamic globular complex. 

In addition to its nutritional role in providing protein for the neonate, the casein micelle also solubilises calcium and phosphate at concentrations well above the level that would normally precipitate in solution, allowing for nutrients to be passed from the mother to her offspring. Exosomes are another nanostructure found both in human and bovine milk and within other body fluids.
Other naturally occurring protein nanostructures include the triple helix of collagen in muscle tissue, from which gelatin is produced upon partial hydrolysis of collagen. This nanofibrillar structure is widely present in foods and pharmaceuticals. Likewise, polysaccharide-derived nanofibrillar structures such as xanthan and carrageenan bundles, the latter from seaweed, are added to foods and pharmaceuticals to increase viscosity, the report found.
 

Which protein nanostructures can be altered by processing?
Food processing has the potential to alter the structure of food proteins either as the result of manufacturing or as a consequence of the physicochemical environment a protein encounters during processing, said the study. 
Process variables that can alter structure include elevated temperature or pressure, shear forces applied during mixing, pumping, centrifugation or filtration, the use of sonication, or the interactions that occur between proteins and surfaces that result in adhesion and fouling.
Changes in temperature associated with the heat processing of foods can alter protein structure, potentially on the nanoscale. This often results in amorphous, non-specific, protein aggregates, like the cooking of egg white, which induces a change of the protein structure to an aggregated form that is amyloid-like.

The various studies found that many protein nanostructures are currently consumed by humans every day and are broken down rapidly in the gastrointestinal tract. 
Furthermore, foods processed at the nanoscale may be more easily digestible than their microstructured counterparts and so may provide enhanced nutrition, or act as a delivery system. While recent research has focused on the microstructure of foods, nanostructured components can also be used to add or alter food properties including stability and texture.
 

Should we deliberately introduce protein nanostructures into food?
Evidence to date suggests that there is no simple answer to this question, and that further research will be required, rather than a general solution for all proposed protein ingredients. As an example, amyloid fibrils formed by k-casein under physiological conditions are cytotoxic.

However, both fibril formation and cytotoxicity are inhibited by the presence of b-casein, its natural binding partner in the casein micelle. Thus a homogeneous preparation of k-casein, or fibrils prepared from it, may pose a risk to health, but this risk is substantially lessened in a heterogeneous mixture containing appropriate quantities of b-casein. 

The report also noted that the ability of b-casein to interact with a diversity of relatively hydrophobic proteins in a chaperone manner implies that it could be used in broader context, including as a nanovehicle to enhance the solubility of curcumin, a known natural anticancer and antioxidant polyphenol which, by its nature, is relatively hydrophobic.
 

So, what's the final conclusion?
The combined studies reviewed in the report suggest we should proceed with caution when considering the development of new nanostructures for use in food, especially amyloid fibrils. 
As the report duly noted, the extent to which novel nanostructures may afford new risks has not been adequately resolved, leading to concern within some consumer groups.
This view is totally consistent with the UK Lords Science and Technology Committee, which has also called for caution, suggesting further discussion and the establishment of a list of commercially available products containing nanomaterials maintained by food agencies along with more transparency in the industry.