Effect of post-harvest treatments on the level of glucosinolates in broccoli

Broccoli is a very perishable vegetable with a high water content (around 88%) which leads to rapid dehydration and probably to an alteration in composition if conditions after harvest are not controlled. This study evaluates the glucosinolate pattern and glucosinolate levels in the principal and secondary inflorescences of fresh broccoli cv 'Tokyodome', and after being submitted to some situations which are likely to occur during or after harvest: room temperature (+/-20 degrees C) for 5 days, kept in the fridge at 4 degrees C for 5 days, and frozen after blanching. Another set of material was harvested 5 days later, simulating a post-maturation stage, and analysed. The highest total glucosinolate content was found at commercial maturation with 20 888 and 20 355 mu moles kg(-1) DW in the principal and secondary inflorescences, respectively. Keeping the inflorescences at room temperature caused the most significant (P < 0.05) reductions in total and individual glucosinolates, except for 4-hydroxyindol-3-ylmethyl-, 2-hydroxy-2-phenylethyl- and 2-phenylethyl-, when compared to the other situations. The highest levels (10 925 mu moles kg(-1) DW) of 4-methylsulphinylbutyl-, the precursor of the anti-cancer isothiocyanate sulphoraphane, were found in the inflorescences freshly harvested at commercial stage. Refrigeration at 4 degrees C and freezing were shown to be the best preservation processes for maintaining high levels of these and other glucosinolates in contrast with the other situations. (C) 1999 Society of Chemical Industry.