Total glucosinolate content of local vegetables and effects of processing and storage on broccoli (Brassica oleracea L. var Italica) glucosinolates


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The chemopreventive properties of Brassica vegetables have been attributed to glucosinolates and their corresponding hydrolytic products. In this study, the total glucosinolate levels of stored and processed broccoli florets, as well as those of other locally grown vegetables were determined. Methanol extracts were prepared from fresh, frozen and processed (microwave heated, blanched, steamed, boilded, and stir-fried) broccoli (Brassica oleracea L. var italica) and their total glucosinolate contents were subsequently determined by HPLC analysis of the desulfated derivatives. Raw samples of sixteen other vegetables were similarly analyzed. The levels of the most predominant glucosinolates in broccoli were observed to decrease after frozen storage for up to 14 days. Total and individual glucosinolate concentrations were variably affected by processing. In comparison with the raw sample, glucosinolate concentrations were higher in boiled and blanched broccoli. Stir - frying and steaming however resulted in decreased quantities of total and individual glucosinolates while no significant changes were seen as a result of microwave heating. Broccoli was found to have the highest total glucosinolate content of all samples tested but significant quantities were also observed for other vegetables. Mustard leaves had the second highest total glucosinolate content among Brassica vegetables analyzed, which also included cauliflower florets and red, green and Chinese cabbage. Among the non - Brassica vegetables, the highest glucosinolate content was found for Basella rubra L. (alugbati or Malabar Night Shade) while negligible amounts were present in the popular local vegetable Ipomea aquatica (kangkong). It was evident from the results of this investigation that aside from the quantitative differences, glucosinolates also differed qualitatively among vegetables.





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Glycosides; Broccoli—Analysis; Vegetables—Effect of temperature on

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