AN IMPROVED ANALYTICAL METHOD FOR THE DETERMINATION OF CAROTENES AND XANTHOPHYLLS IN DRIED PLANT MATERIALS AND MIXED FEEDS

Various experiments were performed to evaluate the current Association of Official Analytical Chemists (AOAC) method used for the determination of carotenes and xanthophylls in dried plant materials and mixed feeds. Incorporation of nitrogen gas and antioxidants such as BHT during extraction and saponification increased carotene and xanthophyll contents from 2 to 4% and from 19 to 30%, respectively. Combination of extraction time and saponification time for 16 h increased xanthophyll content by approximately 23%. Cold saponification also resulted in higher xanthophyll contents than hot saponification. A 1:1 mixture of MgO and diatomaceous earth was found suitable to replace silica gel as the adsorbent to separate major carotenoids by open-column chromatography. A binary solvent system of hexane-acetone and a ternary solvent system of hexane-acetone-methanol in different ratios were used to separate carotenes, monohydroxy pigments, dihydroxy pigments and polyoxy pigments. The amounts of beta-carotene and lutein were also substantially increased by using the modified AOAC method.