Optimization of a blanching step to maximize sulforaphane synthesis in broccoli florets

A blanching step was designed to favor sulforaphane synthesis in broccoli. Blanching was optimised through a central composite design, and the effects of temperature (50-70 °C) and immersion time in water (5-15 min) on the content of total glucosinolates, glucoraphanin, sulforaphane, and myrosinase activity were determined. Results were analysed by ANOVA and the optimal condition was determined through response surface methodology. Temperature between 50 and 60 °C significantly increased sulforaphane content (p < 0.05), whilst blanching at 70 and 74 °C diminished significantly this content, compared to fresh broccoli. The optimal blanching conditions given by the statistical model were immersion in water at 57 °C for 13 min; coinciding with the minimum glucosinolates and glucoraphanin content, and with the maximum myrosinase activity. In the optimal conditions, the predicted response of 4.0 μmol sulforaphane/g dry matter was confirmed experimentally. This value represents a 237% increase with respect to the fresh vegetable.