The Effect of Boiling and in Vitro Digestion on the Carotenoid Content of Colored-grain Wheat

The boiling of colored-grain wheat kernels resulted in a more pronounced loss of total carotenoids compared to in vitro digestion (27.3% vs. 12.1%). After both boiling and digestion, the highest carotenoid content was preserved in Citrus and Bona Vita wheats with yellow endosperm (2.34 and 1.88 mu g/g), which is more than six times the content retained in the digested material of red and blue varieties. Esterified carotenoids exhibited subaverage heat-resistance, as their content dropped to 58.0% after boiling, while decreasing only slightly due to digestion (to 53.4%). The stability of free zeaxanthin, lutein, and beta-carotene differed significantly throughout boiling (92.3% > 72.3% > 27.1%) and subsequent digestion (68.3% > 60.1% > beta-carotene was reduced completely). Exposure to high temperatures and other factors in play during digestion (i.e. acidic environment) resulted in lutein E/Z isomerization, mainly reflected by an increase in 9-and 9'-Z-lutein content to 111% and 225%.