Metabolite profiles of glucosinolates in cabbage varieties (Brassica oleracea var. capitata) by season, color, and tissue position

Abstract

Glucosinolates (GSLs) are sulfur-containing anionic secondary metabolites that are precursors of biologically active compounds, such as isothiocyanates, in Brassicaceae. The GSLs found in 10 cultivars of cabbage (Brassica oleracea var. capitata) popularly cultivated in Korea and China were identified and quantified. Three GSL classes (6 aliphatic, 1 aromatic, and 3 indolyl) were identified and quantified using high-performance liquid chromatography mass spectrometry (HPLC-MS) and HPLC. The concentration of these GSLs varied by season (spring- and fall-sown), leaf position (inside and outside), and cabbage color (green and red). The average total amounts of GSLs in the inner and outer sections of green and red cabbages ranged from 8.55–13.5 μmol∙g−1 dry weight. The spring-sown cabbages contained significantly higher GSL concentration (2.3–4.3 times higher) compared to their fall-sown counterparts. The inner sections of cabbages contained 1.1- to 1.8-fold greater GSL concentrations than the outer sections. These results indicate that an increase in temperature induces GSL accumulation in both green and red cabbages. The green cabbage cultivars contained significantly higher concentration of GSLs synthesized from homo-methionine, whereas the red cabbage cultivars had greater amounts of GSLs synthesized from dihomo-methionine, which suggests that the activities of enzymes involved in the elongation of homo-methionine are greater in red cabbages. The fall-sown red cabbages also contained 2- to 3-fold higher contents of GSLs synthesized from tryptophan compared to the spring-sown cabbages. In conclusion, the color of cabbage, tissue position of cabbage, temperature, and rainfall were all significantly correlated with the amount of GSL accumulation in cabbages.