depends on an understanding of the various factors that nor-
mally limit their oral bioavailability (Fig. 2).
Poor release from food matrix: Some bioactive components
have low bioavailability because they remain trapped within
the food matrix. For example, carotenoids may be trapped
within plant cell tissues that are not fully broken down within
the gastrointestinal tract, and therefore they are not released.
Low solubility in gastrointestinal fluids: Many bioactive
components have low bioavailability because they have poor
solubility in the aqueous gastrointestinal fluids, and are there-fore not available for absorption by the epithelium cells. For
example, oil-soluble vitamins and carotenoids have a low solu-bility in gastrointestinal fluids, which limits their bioavailabil-
ity (Fig. 3, page 354).
Transformation in gastrointestinal tract: Certain bioactive
components have low bioavailability because they are chemi-cally changed or metabolized within the gastrointestinal tract.
For example, curcumin undergoes rapid chemical transforma-tion around neutral pH thereby reducing its bioactivity.
Poor absorption by epithelium cells:
Some bioactive com-ponents have low bioavailability because they are not readily
absorbed by the epithelium cells. In other words, they have
low intestinal permeability.
Each type of bioactive component has its own unique
factors that limit its bioavailability, which depends on its
molecular and physical properties, as well as the nature of the
surrounding food matrix.
Designing excipient foods
to improve bioavailability
Based on knowledge of the major factors that normally limit
bioaccessibility it is possible to design food matrices that
boost the potential health benefits of bioactive components
in natural and processed foods. Some of the potential strat-egies that could be used to achieve this goal are highlighted.
Enhancing release from food matrix: An excipient food may
be designed to contain ingredients that facilitate the break-down of the food matrix, and therefore the release of the bioac-tive component. Examples include specific enzymes, chelating
agents, surfactants, acids, or bases that disrupt food structures
that normally prevent bioactive release.
Improving solubility in gastrointestinal fluids: An excipient
food may contain ingredients that improve the solubility of the
bioactive components within the gastrointestinal fluids. For
example, the solubility of highly lipophilic components can be
improved by including long chain triglycerides in an excipient
food. These triglycerides are converted into free fatty acids
and monoglycerides in the small intestine, which form mixed
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