Microwave cooking increases sulforaphane level in broccoli

Sulforaphane (SFR), an anticarcinogenic compound, forms from the hydrolysis of glucoraphanin (GLR) in broccoli. Cooking methods have been shown to affect broccoli GLR and SFR levels, but little is known about the effect of lightly cooking processes on them. In this study, the effects of microwave and low-temperature cooking on GLR and SFR contents in broccoli were investigated. Both microwaving and mild heating increased the GLR and SFR levels in broccoli compared to the raw samples (without any treatment). In particular, SFR level was significantly low under 40°C and dramatically increased from 40 to 60°C, but nothing was detected at 70°C. Compared with conventional heating, microwave heating increased the GLR and SFR yield by about 80% at 50 and 60°C. Microwave power level also influenced the SFR contents. At the same temperatures (50 and 60°C), high-power microwave (950 W) with a short time produced over 40% more SFR than low-power microwave treatment (475 W). Hence, mild heating by microwave could increase the GLR and SFR levels in broccoli, and high-power microwave heating with temperature control at 60°C could retain higher bioavailability of these bioactive compounds in broccoli.