Changes in Compositions of Galactolipids, Triacylglycerols, and Tocopherols of Lettuce Varieties (Lactuca sativa L.) with Type, Age, and Light Source

Authors: Byrdwell, W Craig; KUBZDELA, NICOLA - Stanford University; Goldschmidt, Robert

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/21/2020
Publication Date: 12/11/2020
Citation: Byrdwell, W.C., Kubzdela, ., Goldschmidt, R.J. 2020. Changes in Compositions of Galactolipids, Triacylglycerols, and Tocopherols of Lettuce Varieties (Lactuca sativa L.) with Type, Age, and Light Source. Journal of Agricultural and Food Chemistry. 4:242-248. https://doi.org/10.1016/j.jfca.2020.103631.
DOI: https://doi.org/10.1016/j.jfca.2020.103631

Interpretive Summary: The effects of light source, age of harvest, and cultivar on the contents of vitamin E and lipids (fatty molecules that make up cell walls and other components) in green and red leaf lettuce were studied. Samples of romaine and lolla rossa were grown under natural light in a greenhouse and four models of grow lights, and were harvested and analyzed at 3 weeks (microgreens) and 8 weeks. Analysis indicated that vitamin E started at the same levels in both varieties of greenhouse-grown lettuce, and did not change in romaine, whereas it approximately tripled in lolla rossa, and approximately tripled in lolla rossa by two LED lighting treatments. There were no universal trends in vitamin E across all samples and varieties. On the other hand, distinct trends were seen in the compositions of lettuce oil. There were was a shift in lettuce oil components toward more polyunsaturated oil components.

Technical Abstract: The effects of light source, age of harvest, and cultivar on the contents of galactolipids (GALs), triacylglycerols (TAGs), diacylglycerols (DAGs), and tocopherols in green and red leaf lettuce varieties (Lactuca sativa L.) were studied using high performance liquid chromatography with triple parallel mass spectrometry (LC1MS3). Samples of romaine and lolla rossa were grown under natural light in a greenhouse and four models of grow lights, and were harvested and analyzed at 3 weeks (microgreens) and 8 weeks. Selected reaction monitoring (SRM) by atmospheric pressure chemical ionization (APCI) MS indicated that a-tocopherol started at the same levels in both varieties of greenhouse-grown lettuce, and did not change in romaine, whereas it approximately tripled in lolla rossa, from 3.4 ± 0.3 ug/mL to 9.9 ± 0.7 ug/mL, and approximately tripled in lolla rossa by two LED lighting treatments. There were no universal trends in a- or g-tocopherols across all samples and varieties. Conversely, distinct trends were seen in the compositions of TAGs quantified using atmospheric pressure photoionization (APPI) MS. There were substantial increases in TAGs containing linolenic acid (Ln) with corresponding decreases in TAGs containing mostly linoleic acid (L). GALs ranged from 2.67 ± 0.06 times the sum of DAGs plus TAGs for a 3 week green lettuce to 32.71 ± 0.75 times that sum for an 8 week red lettuce, in general being higher in red than green lettuce. The major GALs were dilinolenoyl-monogalactosyldiacylglycerol (LnLn-MGDG) and dilinolenoyl-digalactosyldiacylglycerol (LnLn-DGDG), representing averages of 53.6 ± 1.4% and 33.7 ± 2.3% of galactolipids, respectively.