Nanoemulsions: An emerging platform for increasing the efficacy of nutraceuticals in foods.

Both whole and processed foods contain numerous bioactive substances that improve human health and performance, including macronutrients, micronutrients, and nutraceuticals. Many of these substances are strongly hydrophobic and chemically labile, which can diminish their beneficial health effects, since only a small fraction of the ingested amount is actually absorbed and utilized by the body. In the gastrointestinal tract, the overall bioavailability of a hydrophobic substance is determined by its bioaccessibility, transformation, and absorption. The design of functional foods with enhanced biological activity depends on identifying the relative importance of these three different processes for specific bioactive substances, and then using this knowledge to optimize the nature of food matrices to boost bioavailability. In this review, we focus on the utilization of oil-in-water nanoemulsions for this purpose because their compositions, structures, and properties can be easily manipulated. Nanoemulsions can be used as delivery systems where the hydrophobic bioactive substances are loaded into the oil phase either before or after homogenization. Alternatively, they can be utilized as excipient systems. In this case, the bioactive substances are located within an existing food product (such as a fruit or vegetable), which is then consumed with a specially-designed excipient nanoemulsion (such as a sauce, dressing, or cream). Research has shown that for both delivery and excipient systems, the oral bioavailability of hydrophobic bioactives can be enhanced considerably in the presence of a nanoemulsion, provided its properties have been carefully designed. This review article outlines the principles of the design of nanoemulsion-based delivery and excipient systems for boosting the bioavailability of hydrophobic bioactive substances.