Nothing to be salty about: Nutrient and salinity stress improves carotenoid bioaccessibility from spinach

Authors: Dzakovich, Michael

Submitted to: American Society for Nutrition
Publication Type: Abstract Only
Publication Acceptance Date: 3/22/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Micronutrient shortages are a persistent issue for astronauts on long space missions, especially for minerals and fat-soluble vitamins like vitamin A and its precursor carotenoids such as B-carotene. While various factors have been studied to see how they affect carotenoid levels, their impact on bioaccessibility – how much is made available for absorption by the body – is still unclear. We hypothesized that controlled stress from nitrogen and salinity might actually increase how much carotenoids from spinach the body can absorb. To test this, we grew four types of spinach in a controlled environment and then exposed them to different levels of stress: either 50% or 75% less nitrogen in their nutrient solution, or a mild dose of salt. After three weeks, we harvested the plants, analyzed their carotenoid levels, and tested how easily these nutrients could be absorbed by the body through a lab simulation of digestion. Surprisingly, both nitrogen stress levels reduced the yield of the spinach plants and how easily the body could absorb carotenoids compared to the normal conditions. However, the mild salt treatment actually increased carotenoid bioaccessibility without changing the overall amount of carotenoids in the leaves or the total yield of spinach. Our findings suggest that mild salt stress might be a way to produce plant foods with higher levels of these important nutrients that the body can absorb more efficiently. These results are crucial for investigating the environmental contributions towards plant nutritional quality.

Technical Abstract: Micronutrient deficiencies, including minerals and fat-soluble vitamins, remain a problem for children in developing nations. Among the fat-soluble nutrients include vitamin A and precursor carotenoids such as B-carotene. Although a variety of stressors have been explored to influence the concentration of carotenoids, the impact of stress on bioaccessibility, or the amount made available for absorption by the body, remains poorly defined. We hypothesized that controlled nitrogen and salinity stress would improve carotenoid bioaccessibility from spinach. Four varieties of spinach were grown under controlled environment conditions (22/18 C day/night; 150 umoles/m2/s photosynthetically active radiation,12-hour photoperiod) and one week after transplant subject to 50% or 75% nitrogen(modified Hoagland’s solution), or a mild salinity treatment (20/10 uM CaCl2/NaCl). After three weeks of treatment, plants were harvested, analyzed for carotenoids, and subject to a three-stage in vitro digestion to determine bioaccessibility. Both nitrogen treatments decreased fresh/dry mass and carotenoid bioaccessibility relative to controls. However,the mild salinity treatment increased carotenoid bioaccessibility without affecting total carotenoid concentration in leaf tissues or total yield. Our data suggest that mild salinity stress can be leveraged to generate plant foods with greater delivery potential of fat-soluble phytochemicals. These results are crucial for investigating the environmental contributions towards plant nutritional quality.