Changes in compositions of galactolipids, triacylglycerols, and tocopherols of lettuce varieties (Lactuca sativa L.) with type, age, and light source

Abstract

The compositions of molecular species of structural lipids and storage lipids of two types of lettuce leaves, romaine (green leaf) and Lolla Rossa (red leaf), are reported. Lettuce was harvested at two ages, three weeks (microgreens) and eight weeks (mature), and analyzed by liquid chromatography-mass spectrometry. Samples grown under natural light in a greenhouse were compared to those grown under grow lights. Compositions of molecular species of galactolipids (GALs), which are structural lipids, and triacylglycerols (TAGs) and diacylglycerols (DAGs), which are storage lipids, were examined relative to type (cultivar), age, and light source. GALs were most abundant, and the predominant molecular species were dilinolenoyl-monogalactosyldiacylglycerol (LnLn-MGDG) and dilinolenoyl-digalactosyldiacylglycerol (LnLn-DGDG), averaging 53.6 ± 1.4 % and 33.7 ± 2.3 % of galactolipids, respectively. TAGs containing linolenic acid (Ln) increased from three to eight weeks, especially LnLnL, LLLn, PLLn (P is palmitic acid and L is linoleic acid), and LnLnLn, with corresponding decreases in TAGs containing mostly linoleic acid, especially LLL, LLP, and LLO (O is oleic acid). α-Tocopherol started at similar levels in both varieties of greenhouse-grown lettuce, and it approximately tripled in Lolla Rossa, from 3.4 ± 0.3 μg/g to 9.9 ± 0.7 μg/g, by two LED lighting treatments.