Functional foods characterization at the nanoscale using SAXS

Functional food, is food that delivers additional health benefits beyond basic nutrient contents such as fat, proteins and carbohydrates. Simple examples include fortified breakfast cereals and probiotics. Rapid growth in the health and wellness market, combined with increasing health awareness among customers means that functional food is now one of the most active areas of nutritional science research.^1-3

Recent research focuses on preserving the integrity of functional ingredients while ensuring they are readily available to the body. The properties of naturally occurring vesicles and micelles found in nature such as found in plants or animals are very attractive to food scientists as our digestive system has evolved to release and absorb their contents. Recent developments in characterization techniques have improved the understanding of naturally occurring bio-architectures and how they self-assemble, enabling the creation of synthetic liposomes that closely resemble those found in nature.^4-7

Some of the challenges food scientists face at the moment are the design of new solutions for functional food protection, controlled release, and increased bioavailability of compounds such as vitamins, minerals, antioxidants, aroma compounds, and oils. ^5,9-13 Recent research has focused on designing a large variety of self-assembled nanocarriers for food delivery including lipid and protein-based microemulsions, liquid crystalline phases, and nanostructured dispersions.

The ability of nanocarriers to stabilize functional food compounds during processing and release their contents when desired is heavily dependent on their composition and structure. Characterizing self-assembled nanostructures and understanding how nutrient loading and assembly conditions affect their final structure and properties is an essential part of designing systems for functional food delivery. One analysis technique that is particularly suited to characterizing nanocarriers and dispersions in functional foods is small-angle X-ray scattering (SAXS).¹⁴

SAXS is an analytical technique that allows characterization of nanocarrier dispersions in their intended environment. It requires no sample preparation such as drying, freezing and staining steps usually encountered in other analytical techniques, thus ensuring sample is under the same conditions as in food products.

During SAXS analysis, X-ray photons scatter from electrons in the sample to determine nanoscale differences in density, providing nanoscale structural information about mesophases, nanostructures, and dispersions. SAXS enables the scientist to observe the impact of factors such as nutrient loading and external conditions such as dilution and pH changes on the final structure and properties of the nanocarriers.^14-16

As an example, SAXS can be used to characterize the liquid crystalline phases of nanostructured lipid miniemulsions (submicron particles) for formulation of mixture including food-grade ingredients. The figures below are an extract of a SAXS characterization study conducted on miniemulsions of food flavor compounds by scientists from University of Orleans. An important conclusion of this study is that despite very similar chemical composition, the emulsions show a different structural (so called phase) behavior when changing the flavor amount, which could impact their release characteristics. More over, it is shown that up to 20% or 25% of flavor compound (relative to lipid mass), depending on its type, can be added before a major structural change of the self-assembled miniemulsions  is observed. Above such flavor content a drastic loss of order is observed, this indicates less stable structures with increased likelihood of flavor compounds leaking out.¹³

Use of SAXS to characterize nanostructured liposomes