Tocopherols, Phylloquinone, Ascorbic Acid, and Sugar Contents in Hydroponically Grown Lettuce

Growing vegetables in controlled environments (CEs), such as hydroponics, aquaponics, and vertical struc-tures, is a rapidly expanding industry in Florida and the United States, especially in nearby urban areas. Although let-tuce (Lactuca sativa) is still mostly produced in fields, growing in CEs proximal to urban areas has become increasingly popular because it may facilitate reduced transportation time and associated postharvest degradation. Lettuce is among the top-most consumed vegetables in the United States and could provide some of the nutrition missing in the US diet. This research was planned to understand the levels of some vitamins that are key for human health, including vitamin E (tocopherols), vitamin K1 (phylloquinone), and vitamin C (ascorbic acid), in lettuce grown in greenhouse hydroponics. Lettuce germplasm was grown using the hydroponic nutrient film technique system in three greenhouse experiments: at the beginning, middle, and end of the Florida, USA, growing season (from Aug 2020 to Mar 2021). Genetic variation for these vitamins were found among the germplasm tested in the four morphological types of lettuce, romaine, Boston, Latin, and leaf. In addition, a sugar analysis was conducted in this germplasm, of which fructose was the most abundant sugar. A significant genotype x environment (G x E) interaction was observed, indicating that the levels of these com-pounds, especially vitamins, was environment dependent. However, the presence of certain non-crossover G x E interac-tions indicates that selecting lettuce in a representative environment could result in new cultivars with higher vitamin content. This research marks the initial steps to improve lettuce for these vitamins, which can contribute to better health of US consumers, not for the highest amount of these compounds in lettuce but for the offset due to its high consumption.

Automated summary

Growing vegetables in controlled environments is a growing industry in Florida and the US. Lettuce is a popular vegetable in the US and growing it in controlled environments near urban areas can reduce transportation time and degradation. Genetic variation for key vitamins in lettuce was found among different lettuce types, and selecting lettuce in a representative environment could result in cultivars with higher vitamin content.