Effect of ultrasonic pretreatment on tocochromanol and carotenoid biofortification in maize (Zea mays L.) seedlings

摘要

BACKGROUND Maize is a sought-after food crop because it is micronutrient-rich and affordable. It is an excellent source of carotenoids and tocochromanols. To investigate ways to enhance the micronutrients in maize, we grew maize seedlings with ultrasonic pretreatment to study the effect of ultrasound pretreatment on the biofortification of tocochromanols and carotenoids using high-performance liquid chromatography and real-time quantitative polymerase chain reaction. RESULTS Four tocopherol isomers, three tocotrienol isomers and six carotenoid components were measured in maize seedlings. Compared with the untreated maize seedlings, carotenoid content increased and reached the highest level at 8 min ultrasonic pretreatment (19.21 +/- 0.44 mu g g(-1) fresh weight (FW)), but tocotrienol content evidently decreased. Tocopherol dropped at first but began to rise after 8 min ultrasonic pretreatment (258.1 +/- 6.4 mu g g(-1) FW). In particular, zeaxanthin in maize seedlings doubled after pre-sonication, while lutein was boosted to 11.81 +/- 0.20 mu g g(-1) FW. Ultrasonic pretreatment changed the predominant component of tocochromanols in maize seedlings from gamma-tocotrienol to alpha-tocopherol, with the latter content being 1.3 times higher than in the untreated group. Up-regulation of key genes involved in the biosynthesis of tocopherols and carotenoids in maize seedlings occurred as a result of both 2 min and 6 min sonication pretreatment. In particular, ZmHPPD, (Zm)ZE, (Zm)ZDS and (Zm)MPBQ-MT could partly explain the changes in these phytochemicals. CONCLUSION Wet ultrasonic pretreatment could increase tocopherol and carotenoid accumulation in maize seedlings but decrease tocotrienol synthesis. Some up-regulating genes are related to relevant syntheses, such as ZmHPPD, (Zm)ZE, (Zm)ZDS and (Zm)MPBQ-MT, which could influence the accumulation of tocopherols and carotenoids after ultrasonic pretreatment.

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