Location: Food Quality LaboratoryTitle: Summer (sub-arctic) versus winter (sub-tropical) production affects on spinach leaf bio-nutrients: Vitamins (C, E, Folate, K1, provitamin A), lutein, phenolics, and antioxidants) Author
Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/8/2013
Publication Date: 7/8/2013
Citation: Lester, G.E., Makus, D.J., Hodges, D.M., Jifon, J. 2013. Summer (sub-arctic) versus winter (sub-tropical) production affects on spinach leaf bio-nutrients: Vitamins (C, E, Folate, K1, provitamin A), lutein, phenolics, and antioxidants. Journal of Agricultural and Food Chemistry. 61:7019-7027. Interpretive Summary: It is an accepted line of thought: that as cool-season crop production is moved to higher latitudes (sub-tropics to the sub-arctic), due to global climate change pressures, exposure to longer light duration will provide higher nutritional concentrations. Which is plausible as photosynthesis is bio-nutrient (vitamin C, B9, E, K and carotenoids) dependent for its functioning and is triggered by light, but no studies exist. Using spinach plants grown in both the sub-tropics and the sub-arctic we found that vitamin C was higher in the sub-tropics, whereas folate (B9) was higher in the sub-arctic, and phylloquinone (vitamin K) had a contrasting cultivar response to latitude and day-length. Lutein and total carotenoids were unaffected by latitude; whereas alpha-tocopherol (the bio-active form of vitamin E) was absent in sub-arctic spinach but was present in subtropical grown spinach. This study is important for other plant physiologists, food scientists, climate researchers, spinach breeders, and growers for an understanding of plant bio-nutrient responses to changing environmental conditions.
Technical Abstract: Comparison of spinach (Spinacia oleracea L.) cultivars Lazio and Samish grown during the summer solstice in the sub-arctic versus the winter solstice in the sub-tropics provided insight into interactions between plant environment (day length, light intensity, ambient temperatures), cultivar and leaf age/maturity/position affecting bio-nutrient concentrations of vitamins (C, E, folate , K, provitamin A), lutein, phenolics, and antioxidants. Growing spinach during the winter solstice in the sub-tropics resulted in higher leaf dry matter, oxidized ascorbic acid (AsA), alpha- and gamma-tocopherol and total phenols, but lower reduced AsA, alpha-carotene, folate and total anti-oxidants compared to summer solstice-grown spinach in the sub-arctic. With the exception of higher oxidized AsA, and lower alpha- and gamma-tocopherol in ‘Samish’ compared to ‘Lazio’, cultivars were similar in other bio-nutrients. An increasing bio-nutrient concentration gradient from bottom to top canopy leaves occurred in most responses measured and was almost always linear and in some cases both linear and quadratic. In some cases where the polynomial fit was not statistically significant, the same trend was apparent. Total phenols and anti-oxidants were the only bio-nutrient responses which decreased with leaf position (top< middle < bottom leaves). These results suggest that the summer sub-arctic versus winter sub-tropic growing conditions can play a major role in affecting the bio-nutrient status of spinach, in addition to leaf position (age) and cultivar. Further the longitudinal growing environment, as we experience global climate change, should also be reported along with experimental variables commonly found in bio-nutrient content studies.