Identification and quantification of glucosinolates in local Brassica speciesvarieties and study of the effect of cooking methods on in vitro accessibility of glucosinolates products

Abstract

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Glucosinolates are a large group of plant secondary metabolites. They are common in all economically important species of Brassicca vegetables. Reduced risk of certain cancers is found to associate with consumption of Brassicaceae family vegetables which contain glucosinolates. In the present study, four major glucosinolates (sinigrin, glucoraphanin, glucotropaeolin and gluconasturtiin) were identified in the tested samples and quantified using High Performance Liquid Chromatography (HPLC) combined with photodiode-array detection (PDA). Accordingly, five most locally popular Brassica species namely, broccoli (Brassica oleracea var. italica), white cabbage (Brassica oleracea var. cap itata) , red cabbage (Brassica oleracea var. cap itata) , radish (Raphanus sativus) and cauliflower (Brassicaoleracea var. botrytis) were analysed for their glucosinolates profile in raw, cooked and in vitro digested samples. The stability of glucosinolates was evaluated in selected vegetables under different cooking methods and in vitro gastrointestinal digestion methods. It was observed that frying is the best method to preserve glucosinoItes in vegetables, compared with soups or vegetables cooked with coconut milk. It was found that the in vitro gastric digestion of vegetable varieties causes high losses In individual glucosinoltes (~70%). After the pancreatin-bile salts mediated digestion, an additional decrease in individual glucosinoltes was observed (~20%). When the Brassicca vegetables were subjected to complete in vitro gastro intestinal digestion, the amount of glucosinolates retained were approximately 10%. This high percentage of loss during the digestion process could be due to the degradation of glucosinolates either to nitriles or to secondary reaction products depending on the gastro intestinal pH conditions.