Distribution of carotenoids in endosperm lipid fractions of maize kernel

Part of maize kernel lipids are located in endosperm where they can occur as free lipids (FL), as lipids weakly bound to the surface of starch granules [bound lipids (BL)], and as lipids located in the structure of the starch [starch lipids (SL)]. Important compounds in the maize endosperm are carotenoids, tetraterpene pigments that exhibit numerous health-promoting effects. Since carotenoids are lipophilic compounds probably related to endosperm lipids, the aim of this study was to evaluate the distribution of carotenoids among lipid fractions. The endosperm of 20 commercial maize hybrids was separated from the kernel. Lipid fractions in the endosperm were recovered sequentially, allowing simultaneous sequential isolation of carotenoids. The FL and BL and the corresponding carotenoids were extracted at room temperature with n-hexane and water- saturated n- butanol, respectively. The SL and the carotenoids in this fraction were extracted with n-propanol-water solution at 85 °C to ensure starch gelatinization. Individual and total carotenoids were quantified by HPLC. In the endosperm of tested hybrids, FL content ranged from 0.74 to 1.17%, while BL and SL were present in much lower quantities (0.12-0.56 and 0.13- 0.75%, respectively). The highest portion of carotenoids was found in the fraction BL, averaging 73.84% of the total endosperm carotenoids, while carotenoid content in FL and SL was substantially lower (13.88 and 12.29%, respectively). The distribution of carotenoids varied greatly among the tested hybrids ; the average ranges were 5.29-37.52% for FL fraction, 48.90-90.53% for BL fraction and 2.35- 28.90% for SL fraction. The content of lutein, zeaxanthin, α- and β-cryptoxanthin and total carotenoids in the BL fraction increased with increasing BL and total endosperm lipid content (P < 0.05). On the other hand, the content of individual and total carotenoids in FL fraction decreased with their increasing content in SL and total endosperm fraction (P < 0.05). The carotenoids in the FL and BL fractions present non-starch compounds, whereas the carotenoids in SL are contained within the starch granules. Consequently, 87.72% of the carotenoids in maize are located in the lipoprotein layer outside starch granules in the endosperm matrix.