All trans-cis isomers content of sweet potatoes (Ipomoea batatas (L) Lam) as influenced by different levels of nitrogen fertilizer application were determined by high performance liquid chromatography (HPLC). The nitrogen fertilizer treatments were four nitrogen levels of 0 (control), 40, 80, 120 kg N/ha and four varieties of sweet potatoes: White fleshed TIS87/0087 and TIS8164, orange-fleshed, Ex-Igbariam and CIP Tanzania. The study area was Umudike Southeast Nigeria, located at latitude 05°29’N and longitude 07°33E, and at elevation of 122 m above sea levels. Nitrogen fertilizer significantly (P<0.05) increased trans-cis isomers of β-carotene with incremental nitrogen fertilizer application up to 80 kg N/ha. TIS87/0087 and Ex-Igbariam varieties gave the highest trans-cis isomers of β-carotene at 40 to 80 kg N/ha when compared with the control (0 kg N/ha). Nitrogen fertilizer application above 80 kg N/ha did not increase β-carotene yield significantly (P>0.05) for the varieties studied except CIP Tanzania. β-carotene (trans-cis isomers) has the potential to improve vitamin A status among the vulnerable groups in Southeast Nigeria. Sweet potato being a stable crop in Southeast Nigeria can be effectively used as a vehicle for improving the Vitamin A intake in this ecological zone through biofortification with β-carotene. With nitrogen fertilizer increasing sweet potato production in this ecological zone, the evaluation of the trans-cis isomers of β-carotene content was a major objective.
Key words: β-carotene, trans-cis isomers, sweet potato varieties, nitrogen fertilizer application.
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