Influence of blanching and freezing broccoli (Brassica oleracea var. italica) prior to storage and cooking on glucosinolate concentrations and myrosinase activity

Glucosinolates contribute to the chemoprotective effects of Brassica vegetables. The influence of blanching and freezing broccoli, followed by storage or cooking, on its glucosinolate concentration and myrosinase activity was investigated. Myrosinase activity was reduced by 93%, while glucosinolate concentration was unaltered after blanch-freezing broccoli. Blanch-frozen Brassica retained the glucosinolate content of its fresh counterpart after storage at T = -20 degrees C for up to 90 days. Fresh or blanch-frozen broccoli was stir-fried, boiled, boiled and kept hot for 2 h, or left uncooked. Stir-frying retained the highest glucosinolate concentration and myrosinase activity, regardless of pre-cooking. Boiling and keeping blanch-frozen broccoli hot completely denatured myrosinase and decreased glucosinolate concentration by 42%. Aromatic and indole glucosinolates were reduced to a larger extent than aliphatic glucosinolates, especially when boiled broccoli was kept hot. The final concentration of glucosinolates in Brassica is influenced by cooking, while the myrosinase activity is modified by pre-treatment and subsequent cooking.