Abstract
Raphanus sativus (L.) var. caudatus Alef (Thai rat-tailed radish), Brassica juncea (L.) Czern. (leaf mustard) and Brassica juncea (L.) Coss. var. sareptana Sinskaja (mustard green) are cruciferous vegetable commonly consumed in Thailand and Asian countries. The vegetables were extracted with different solvents namely methanol, hexane and water prior to total phenolic content (TPC), phenethyl isothiocyanate (PEITC) content and antioxidant activity by ferric reducing antioxidant power (FRAP) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay were determined. Effects of gastrointestinal digestion on stability of these characteristics were investigated. It was found that the order of extraction efficiency for high bioactive compounds and antioxidant activity was water> methanol> hexane. Among vegetables, mustard green showed the highest TPC, PEITC, FRAP and DPPH values being 19.78±0.01 g GAE, 9.65 ± 1.08 µmol, 8.18±0.01 µM FeSO4 and 7.75±0.31 µM TE per 100g, respectively. Decreases in DPPH (30.6-53.5%), FRAP (49.0-88.0%) and PEITC (27.2-56.7%) values were slightly higher than TPC (27.9-41.6%) after in vitro digestion. It can be said that Thai cruciferous vegetables contain substantial chemical property and this may promote their health protection but the stability through digestive system should be warranted.
Highlights
Many vegetables are categorized within the family Cruciferae.The most common cruciferous vegetables are watercress, Brussels sprouts, broccoli, cabbage, kai choi, kale, horseradish, radish and turnip
The ranges of total polyphenol in mustard green and Thai rat-tailed radish were similar to that reported in green tea and black tea which varied from 21.02 ± 1.54 to 14.32 ± 0.45 and 17.62 ± 0.42 to 8.42 ± 0.55 g Gallic acid equivalent (GAE)/100 g, respectively[19]
Dietary polyphenols has been reported for their sensitivity to alkaline condition in intestine where structural changes lead to chemical property alteration[25].There are many types of phenolic compounds and each of which has different stability in acid-base conditions
Summary
Many vegetables are categorized within the family Cruciferae.The most common cruciferous vegetables are watercress, Brussels sprouts, broccoli, cabbage, kai choi, kale, horseradish, radish and turnip. Recent scientific research has focused on health benefit effect of cruciferous vegetables due to their high content of beneficial substances, glucosinolates and their metabolites such as isothiocyanates (ITCs)[1]. Isothiocyanates are a group of secondary metabolites which are naturally formed prior to hydrolysis of glucosinolates by the plant enzyme, myrosinase. One such important ITC is phenethyl isothiocyanate (PEITC), which has been shown to be a dominant phytochemical in cruciferous vegetables[3]. Bioavailability of bioactive compounds from food following oral intake depends largely on their stability in human digestive system[10]. Study of the digestive fate of bioactive food compounds can help to improve performance and, promote health benefits. The effects of digestion system on these characteristics were evaluated employing in vitro study
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