Abstract
The increased global mortality caused by the rise in chronic diseases can be reduced by the consumption of antioxidant-rich foods. Leafy green kale (Brassica oleracea var. sabellica) has high nutritional value due to its high antioxidant content and its consumption is highly correlated with a reduced risk of developing some chronic diseases. The paper focuses on examining the effects of two different mineral nutrients – neodymium and potassium humate – on the accumulation of flavonoids, vitamin C, phenolic compounds, carotenoids and malondialdehyde (MDA) content in field-grown leafy green kale. Leaves from treated plants were collected at three stages of maturity –14 weeks, 18 weeks, and 22 weeks and subjected to spectrophotometric analysis. The results showed that the stimulatory effect of both mineral nutrients on the phytochemicals varied at the different growth stages - the highest significant effect of neodymium has been mostly observed at week 18 with high flavonoid, vitamin C, and carotenoid levels. Phenolic compounds for this variant are the same as in the control samples, while the level of malondialdehyde was reduced by 21.8%, signifying increased antioxidant activity. The rare earth element primarily maintained some phytochemical content at weeks 14 and 22. Following soil treatment with potassium humate, the levels of studied phytochemical compounds were either maintained or elevated at weeks 14, 18, and 22. Humic acid exerted the greatest decrease in malondialdehyde content in kale at week 14, indicating a reduction in the lipid peroxidation process in leaves. Accordingly, the harvest date of leafy green kale (Brassica oleracea var. sabellica) should depend on the type of mineral nutrient applied. The obtained results provide information that may be relevant to the production of functional varieties and enhance the nutritional and possibly the economic value of kale.
Highlights
The worldwide outbreak of chronic diseases is an increasing problem that threatens the world’s population today
Flavonoid content in plants treated with humate increased by 13.0%, while no change occurred in plants with neodymium treatment
24.3% at week 14, at week 18 neodymium increased vitamin C levels in kale by 36.0%, approximately three-fold the effect induced by humate (13.4%)
Summary
The worldwide outbreak of chronic diseases is an increasing problem that threatens the world’s population today. Increasing evidence suggests that these diseases are associated with lifestyle, stress, and under-consumption of antioxidant-rich fruits and vegetables (Gakidou et al, 2017; Campbel et al, 2020). This popular understanding of how diet affects diseases has created a market for functional foods, that is, foods that satisfy hunger and provide necessary nutrients for humans and aid in the prevention of or treatment of diseases (Chiu et al, 2018; Santini et al, 2018). Vitamin C and carotenoids are major antioxidants in Brassica vegetables and contribute more than 80% to their total antioxidant capacity. Carotenoids are essential biological antioxidants that are associated with the prevention of cancers, cardiovascular diseases and some degenerative diseases such as macular degeneration (Lee et al, 2020)
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