Myrosinase in leafy brassica

Abstract

The cruciferous vegetables, which include broccoli, cabbage, cauliflower, and kale, are one of the healthiest and most nutritious vegetable groups. These vegetables contribute almost exclusively to our intake of glucosinolates, which produce metabolic breakdown products that appear to protect against cancer. Over the years, much attention has been given to the study of glucosinolates but few to myrosinase (EC 3.2.3.1), the -thioglucosidase enzyme responsible for the hydrolysis of the intact glucosinolates. The potential of some intrinsic and extrinsic factors for controlling/altering activity of myrosinase from cruciferous vegetables was investigated in this project. The changes in chlorophyll concentration, chlorophyll fluorescence parameters, and total anti-oxidant capacity of these vegetables under different environment and/or treatment were also determined. Using sinigrin as the substrate, the optimum condition for myrosinase assay in Chinese flowering cabbage and Chinese kale was achieved at 35~40A?C and pH 6~6.5. The following parameters, chlorophyll concentration and chlorophyll fluorescence parameters, total anti-oxidant capacity, myrosinase activity and total soluble protein concentration, were totally different in six commonly edible Brassica vegetables consumed by Asian people. Post harvest storage at cooler temperatures could efficiently delay the symptoms of senescence (in terms of chlorophyll concentration, total anti-oxidant capacity and myrosinase activity) in both Chinese flowering cabbage and Chinese kale. Nitrogen concentration in the fertilizer did not affect the phytochemical properties (chlorophyll concentration, total anti-oxidant capacity or myrosinase activity) of Chinese flowering cabbage seedlings. However, these phytochemical properties were affected by plant organ. Phytochemical properties were highly dependent on the different organs but did not have much correlation with the developmental stage of mature Chinese flowering cabbage. Drought stress had different effects on the phytochemical properties of Brassica vegetables. Lossing chlorophylls and carotenoids was the negative consequence of drought stress; PSII was weakly affected by the imposed drought stress in the Brassica vegetables in this study; Total antioxidant capacity increased with increased severity of drought. Myrosianse activity decreased rapidly in the leaves of Chinese flowering cabbage under drought treatment. Even within the same species, total antioxidant capacity and myrosinase activity could be still quite different. Data and analysis obtained in our study provide extensive profile of myrosinase and other phytochemical properties of Asian Brassica vegetables and help consumers and researchers understand the nutritious value of Brassica vegetables better.