The objective of this study was to develop a model for assessing the bioavailability of carotenoids from meals using an in vitro digestion procedure. A meal was prepared using baby food carrots, spinach, and a meat, plus tomato paste. The aqueous fraction was isolated from digesta to determine the quantity of carotenoids transferred from the food to micelles. The micellarization of lutein (25-40%) exceeded (p < 0.01) that of alpha- and beta-carotene (12-18%) and lycopene (<0.5%). Micellarization of carotenoids was not affected by elimination of the gastric phase of the digestive process. The absence of bile extract prevented the transfer of carotenoids from foods to micelles, whereas omission of pancreatin only reduced the micellarization of the carotenes. Differentiated cultures of Caco-2 human intestinal cells accumulated 28-46% of micellarized carotenoids from the medium after 6 h. These results support the usefulness of the in vitro digestion process as a rapid and cost-effective model for screening the bioavailability of carotenoids from meals.

Lutein and zeaxanthin are selectively accumulated in the lens and macular region of the retina. It was suggested that these xanthophylls protect ocular tissues from free-radical damage that can cause cataracts and age-related macular degeneration. Insights regarding the absorption of dietary xanthophylls for delivery to ocular tissues are limited. Our primary objective was to examine factors affecting the transfer of lutein from foods to absorptive intestinal epithelial cells during digestion. Lutein and other carotenoids present in spinach purée and lutein from a commercial supplement were relatively stable during in vitro digestion. Micellarization of lutein and zeaxanthin during the small intestinal phase of digestion exceeded that of beta-carotene and was greater for xanthophylls in oil-based supplements than in spinach. Apical uptake of lutein from micelles by Caco-2 human intestinal cells was linear for at least 8 h, and accumulation from synthetic micelles exceeded that from micelles generated during simulated digestion. Stimulation of chylomicron synthesis resulted in the secretion of 7.6 +/- 0.1% of cellular lutein into the triglyceride-rich fraction in the basolateral chamber. These data support the use of simulated digestion and the Caco-2 cell model as effective tools for identifying factors affecting absorption of dietary carotenoids.

A carotenoid-rich salad meal with varying amounts and types of triglycerides (TG) was digested using simulated gastric and small intestinal conditions. Xanthophylls (lutein and zeaxanthin) and carotenes (alpha-carotene, beta-carotene, and lycopene) in chyme and micelle fraction were quantified to determine digestive stability and efficiency of micellarization (bioaccessibility). Micellarization of lutein (+zeaxanthin) exceeded that of alpha- and beta-carotenes, which was greater than that of lycopene for all test conditions. Micellarization of carotenes, but not lutein (+zeaxanthin), was enhanced (P < 0.05) by addition of TG (2.5% v/w) to the meal and was dependent on fatty acyl chain length in structured TG (c18:1 > c8:0 > c4:0). The degree of unsaturation of c18 fatty acyl chains in TG added to the salad purée did not significantly alter the efficiency of micellarization of carotenoids. Relatively low amounts of triolein and canola oil (0.5-1%) were required for maximum micellarization of carotenes, but more oil (approximately 2.5%) was required when TG with medium chain saturated fatty acyl groups (e.g., trioctanoin and coconut oil) was added to the salad. Uptake of lutein and beta-carotene by Caco-2 cells also was examined by exposing cells to micelles generated during the simulated digestion of salad purée with either triolein or trioctanoin. Cell accumulation of beta-carotene was independent of fatty acyl composition of micelles, whereas lutein uptake was slightly, but significantly, increased from samples with digested triolein compared to trioctanoin. The results show that the in vitro transfer of alpha-carotene, beta-carotene, and lycopene from chyme to mixed micelles during digestion requires minimal (0.5-1%) lipid content in the meal and is affected by the length of fatty acyl chains but not the degree of unsaturation in TG. In contrast, fatty acyl chain length has limited if any impact on carotenoid uptake by small intestinal epithelial cells. These data suggest that the amount of TG in a typical meal does not limit the bioaccessibility of carotenoids.

Although numerous studies have demonstrated the health benefits of chlorophyll derivatives, information regarding the digestion, absorption, and metabolism of these phytochemicals is quite limited. To better understand the digestion of these pigments, green vegetables including fresh spinach puree (FSP), heat- and acid-treated spinach puree (HASP), and ZnCl(2)-treated spinach puree (ZnSP) were subjected to an in vitro digestion method which simulates both the gastric and small intestinal phases of the process. Native chlorophylls were converted to Mg-free pheophytin derivatives during digestion. Conversely, Zn-pheophytins were completely stable during the digestive process. Transfer of lipophilic chlorophyll derivatives, as well as the carotenoids lutein and beta-carotene, into the aqueous micellar fraction from the food matrix was quantified. Micellarization of total chlorophyll derivatives differed significantly (p < 0.05) for FSP (37.6%), HASP (17.2%), and ZnSP (8.7%). Micellarization of chlorophyll a derivatives was determined to be significantly more efficient than chlorophyll b derivatives in FSP and HASP (p < 0.01), but not in ZnSP (p > 0.05). Intestinal cell uptake of micellarized pigments was investigated using HTB-37 (parent) and clonal TC7 lines of human Caco-2 cells. Medium containing the pigment-enriched fraction generated during digestion was added to the apical surface of fully differentiated monolayers for 4 h. Pigments were then extracted from cells and analyzed by C18 HPLC with photodiode array detection. Both Caco-2 HTB-37 and TC7 clone cells accumulated 20-40% and 5-10% of micellarized carotenoid and chlorophyll derivatives, respectively. These results are the first to demonstrate uptake of chlorophyll derivatives by human intestinal cells and to support the potential importance of chlorophylls as health-promoting phytochemicals.

Cassava, a staple food in sub-Saharan Africa, does not provide adequate amounts of pro-vitamin A (VA) carotenoids and has been targeted for biofortification (i.e. selectively breeding cultivars of increased nutrient density with agroeconomically acceptable characteristics). However, the accessibility of pro-VA carotenoids for absorption in different cultivars of cassava remains unknown. Here, we used the coupled in vitro digestion/Caco-2 cell uptake model to screen the relative accessibility of beta-carotene (betaC) in 10 cultivars of cassava with varying concentrations of betaC. After cooking (boiled for 30 min), the betaC concentration in tubers from different cultivars ranged from less than detectable to 6.9 microg betaC/g cassava. Samples were subjected to simulated oral, gastric, and small intestinal digestion to determine stability and micellarization of betaC. All-trans betaC, 9-cis betaC, and 13-cis betaC were the most abundant carotenoids in cooked cassava and recoveries after digestion exceeded 70%. Efficiency of micellarization of total betaC was 30 +/- 2% for various cultivars with no significant difference in isomers and linearly proportional to concentration in cooked cassava (r = 0.87; P < 0.001). Accumulation of all-trans betaC by Caco-2 cells incubated with the diluted micelle fraction for 4 h was proportional (R(2) = 0.99; P < 0.001) to the quantity present in micelles. These results suggest that all-trans betaC content appears to provide the key selection marker for breeding cassava to improve VA status and that the more complicated screening procedure using in vitro digestion coupled to cell uptake does not provide additional information on potential bioavailability.