Composition Analysis between Kohlrabi (Brassica oleracea var. gongylodes) and Radish (Raphanus sativus)
The major deterring factor of radish consumption is bitter and pungent tastes caused by glucosinolates. Recently kohlrabi is introduced in Korea and mainly cultivated in Jeju Island during winter. Since the texture and taste of kohlrabi are similar to radish, the kohlrabi is expected to substitute radish. This study was done to compare compositional quality between kohlrabi and radish. The kohlrabi contained less reducing sugars, cellulose and pectin than the radish. The kohlrabi has harder texture than the radish. The total amino acid content in the kohlrabi was 2.7-fold higher than that in the radish. Especially hydrophilic amino acids including aspartate, glutamate and arginine, were about 3-fold higher in the kohlrabi, suggesting that the kohlrabi was more palatable than the radish. The total contents of glucosinolates in the radish in inner and outer section were higher than those in the kohlrabi by 12.4- and 28.5-fold, respectively. In a sensory test, the kohlrabi was evaluated less bitter and pungent than the radish. The kohlrabi contained more glucoraphanin, an anticancer compound, than the radish. Furthermore, the sweetness of the kohlrabi was evaluated higher than that of the radish, though kohlrabi contained less reducing sugars, probably due to high contents of hydrophilic amino acids. In conclusion, the kohlrabi was evaluated more favorable in taste and contained more functional compounds than the radish, and thus it can be a good replacement vegetable for radish.
Effect of Color, Season, Tissue Position on Contents of Glucosinolates in Cabbage (Brassica oleracea)
The glucosinolates in 10 cabbage cultivars popularly consumed in Korea and China were identified and quantified. Nine glucosinolates synthesized from homo-methionine (glucoiberin, glucoiberverin, and sinigrin), dihomo-methionine (progoitrin, glucoraphanin, and gluconapin), phenylalanine (gluconasturtiin), and tryptophan (glucobrassicin, 4-methoxy glucobrassicin, and neoglucobrassicin) were detected. The contents of glucosinolates were affected by the season (spring- and fall-sown), the leaf position (inside and outside), and the cabbage color (green and red). The spring-sown cabbages contained significantly higher glucosinolates compared to the counterparts by 2.3~4.3 times. The inner section of cabbages contained more glucosinolates than the outer one by 1.1~1.8 times. These results suggested that the increase temperature induced glucosinolate production. The green cabbages contained significantly higher glucosinolates synthesized from homo-methionine whereas the red ones synthesized from dihomo-methionine, suggesting that the red ones had the activated enzyme producing dihomo-methionine from homo-methionine. The fall-sown red cabbages also contained significantly higher glucosinolates synthesized from tryptophan by two to three fold compared to the counterparts.