Effect of NaCl treatments on glucosinolate metabolism in broccoli sprouts


Rong-fang Guo, Gao-feng Yuan, and Qiao-mei Wang (J Zhejiang Univ Sci B)

Glucosinolate-myrosinase is a unique substrate-enzyme system, in which myrosinases are responsible for glucosinolate turnover. The sprouts of broccoli (Brassica oleracea var. italica) are rich sources of glucosinolates and their hydrolysis products. However, limited information is available about the influence of NaCl treatments on the metabolism of glucosinolates in broccoli sprouts. The aim of the present study was to evaluate the glucosinolate metabolism in broccoli sprouts under NaCl treatment by determining the glucosinolate composition and their contents. The activity of its hydrolysis enzyme, myrosinase, and the content of the main hydrolysis product, sulforaphane, in broccoli sprouts were also analyzed in the present study.To understand the regulation mechanism of NaCl on glucosinolate metabolism in broccoli sprouts, the germination rate, fresh weight, contents of glucosinolates and sulforaphane, as well as myrosinase activity of broccoli sprouts germinated under 0, 20, 40, 60, 80, and 100 mmol/L of NaCl were investigated in our experiment. The results showed that glucoerucin, glucobrassicin, and 4-hydroxy glucobrassicin in 7-d-old broccoli sprouts were significantly enhanced and the activity of myrosinase was inhibited by 100 mmol/L of NaCl. However, the total glucosinolate content in 7-d-old broccoli sprouts was markedly decreased although the fresh weight was significantly increased after treatment with NaCl at relatively low concentrations (20, 40, and 60 mmol/L). NaCl treatment at the concentration of 60 mmol/L for 5 d maintained higher biomass and comparatively higher content of glucosinolates in sprouts of broccoli with decreased myrosinase activity. A relatively high level of NaCl treatment (100 mmol/L) significantly increased the content of sulforaphane in 7-d-old broccoli sprouts compared with the control. These results indicate that broccoli sprouts grown under a suitable concentration of NaCl could be desirable for human nutrition.
NaCl treatment has a concentration-dependent effect on glucosinolate-myrosinase system in broccoli sprouts. NaCl treatments at relatively low concentrations enhanced the growth of the broccoli sprouts. NaCl treatment at the concentration of 60 mmol/L for 5 d maintained higher biomass and comparatively higher content of glucosinolates in broccoli sprouts with decreased myrosinase activity. The application of high concentration, especially 100 mmol/L of NaCl, for 3 d can endow broccoli sprouts with abundant glucosinolates and sulforaphane. The 100 mmol/L NaCl treatment significantly increased the sulforaphane content in 7-d-old broccoli sprouts as compared to the control. These results indicate that broccoli sprouts grown under a suitable concentration of NaCl could be desirable for human nutrition.