Enhanced water dispersibility and permeability through a Caco-2 cell monolayer of ß-cryptoxanthin extracted from kumquats by complexation with casein.

ß-Cryptoxanthin (BCX) possesses potential therapeutic and health benefits. However, BCX absorption is low because of its poor aqueous solubility. In this study, a complex between BCX and casein (Cas) was prepared to improve the water dispersibility and bioavailability of BCX. BCX was recovered quantitatively from freeze-dried kumquat powder through solid-liquid extraction and saponification. The complexation significantly improved the apparent solubility of BCX under acidic and neutral conditions. A cell membrane permeation test using a Caco-2 cell monolayer was performed to evaluate the bioavailability of the BCX-Cas complex. This complex and a blank sample were digested in vitro and added to the apical side of the Caco-2 cell membrane. The quantity of BCX that permeated using the BCX-Cas complex after 24 h was 22.7 times greater than that of the blank. Thus, complexation of BCX with Cas improved dramatically the bioavailability of BCX from a kumquat extract.

Immunostimulatory effect of kumquat (Fortunella crassifolia) and its constituents, ß-cryptoxanthin and R-limonene.

Natural killer (NK) cells play an important role in the innate immune system by eliminating cancer cells and virally infected cells. Aging and stress attenuate the activity of NK cells, thereby increasing the risk of various diseases. In this study, we demonstrated that the consumption of a small number of kumquats in an in vivo model could suppress elevated plasma corticosterone levels and reverse the decline in splenocyte cytotoxicity caused by restraint stress. Our results identified ß-cryptoxanthin (BCX) as an active kumquat component with a NK cell-activating effect, and R-limonene as an active component that mediates not only the anti-stress effect but also NK cell activation by oral administration. In addition, BCX, R-limonene, and R-limonene metabolites were found to enhance IFN-γ production in KHYG-1 cells, a human NK cell line. Collectively, our findings suggest that the ingestion of a few kumquats on a daily basis can help to combat stress and enhance NK cell activity.