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United States Department of Agriculture

Agricultural Research Service

Title: RELATIONSHIP BETWEEN THE NUTRITIONAL VALUE AND THE HEAD STRUCTURE OF LETTUCE

Authors
item MOU, BEIQUAN
item Ryder, Edward

Submitted to: Acta Horticulture Proceedings
Publication Type: Proceedings
Publication Acceptance Date: November 7, 2003
Publication Date: June 8, 2004
Citation: Mou, B., Ryder, E.J. Relationship between the nutritional value & the head structure of lettuce. Acta Horticulturae. 2004. v. 637. p. 361-367.

Interpretive Summary: It is known that iceberg lettuce has much lower vitamin A, vitamin C, Calcium, and iron contents than leaf or romaine lettuce. This experiment was conducted to determine whether the low nutritional value is associated with the head structure. Nutritional content was generally higher in the outer leaves than in the inner leaves of a lettuce head. When we artificially kept the iceberg lettuce head open, its vitamin A, vitamin C, calcium, and iron contents were elevated to a level comparable to leaf or romaine lettuce. Conversely, when leaves of romaine lettuce were closed by tying with wire, its nutrient content was largely reduced. These results suggest that to a large extent the syntheses of these nutrients are light-dependent, the lower nutritional value of iceberg lettuce is due to the enclosure of its leaves in the head structure.

Technical Abstract: Crisphead lettuce has much lower vitamin A, vitamin C, calcium, and iron contents than leaf or romaine lettuce. This experiment was conducted to determine whether the low nutritional value is associated with the head structure. Heads of a crisphead lettuce cultivar 'Salinas' grown in the field were kept open by hand, while leaves of a romaine lettuce cultivar 'Lobjoits' were closed by typing with wire. These plants as well as the normal controls were analyzed for their nutritional contents. The content of vitamin A, Ca, and Fe was higher in the outer leaves than in the inner leaves of a normal lettuce head, while there was little difference in vitamin C content between the two classes of leaves. Artificially opening the lettuce head greatly increased its nutrient content to a level comparable to leaf or romaine lettuce. After the romaine lettuce leaves were closed, the levels of vitamin A and vitamin C dropped to a minimum and the contents of Ca and Fe were also largely reduced. These results suggest that the lower nutritional value of crisphead lettuce is due to the enclosure of its leaves in the head structure. The physiological basis of these findings and their implications for genetic improvement of the nutritional value of lettuce are discussed.

Last Modified: 8/27/2014
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