Abstract
Objectives
This study aimed to systematically investigate a comprehensive list of bioactive components in a commonly consumed Asian leafy vegetable, Brassica rapa. They included polyphenols, fat soluble micronutrients such as carotenoids, tocopherols and phylloquinone, and various glucosinolates (GLs), in addition to the total antioxidant capacity, at three different growth stages.
Methods
Phenolic compounds were measured using C-18 HPLC/MS. Carotenoids, vitamin E and phylloquinone (vitamin K1) were detected using RP-30-HPLC/MS. Glucosinolates were determined using HILIC-HPLC/MS. Different AOX capacities were assessed either using UV-Visible or Fluorescent Spectrophotometer.
Results
Phenolic compounds, such as total flavonoid and hydroxycinnamic acids, were highest at 3-leaf stage and significantly lower in mature plant. The main carotenoids, lutein and β-carotene, remained the same throughout the different growth stages. However, violaxanthin, neoxanthin and β-cryptoxanthin were higher also at 3-leaf stage, and decrease gradually with growth. In contrast, tocopherol concentration continued to increase and was highest at mature stage. There was little change for phylloquinone (vitamin K1) throughout the three studied stages. For the unique components in Brassicaeae, both dominating aliphatic and indolic-GLs concentrations were significantly higher at 1-leaf stage than at mature stage ( > 30x), whereas the aromatic GLs, although of much lower concentrations, continued to increase throughout the growth, and with highest amount at mature stage, suggesting that there is metabolic pathway shift of these secondary metabolites during plant development. In general, antioxidant capacity measured using Scavenging of DPPH radicals, Trolox Equivalent Antioxidant Capacity and Oxygen Radical Absorbance Capacity suggested that there was an insignificant increase of total antioxidant content from seedling to mature vegetable.
Conclusions
The overall findings suggest that most of the nutritional active bio-components were higher at younger stages, either at 1-leaf or 3-leaf stage, except α-tocopherol, with continual accumulation during plant development. These comprehensive profiles of various nutrients should be valuable to the nutritional community.
Funding Sources
National Research Foundation, Prime Minister's Office, Singapore.
Profile of phenolic compounds in Trifolium pratense L. extracts at different growth stages and their biological activities
