Evolution of anticarcinogenic substance in dietary fibre powder from cabbage outer leaves during drying

White cabbage (Brassica oleracea L. var. capitata) is an important source of dietary fibre (DF) and various bioactive compounds, which are claimed to possess antioxidant and anticarcinogenic activities. Sulforaphane, one of the most potent food-derived anticarcinogens, is a hydrolysis product of glucosinolates, which are abundant in Brassica vegetables. As the formation of sulforaphane is via enzymatic reactions and since the compound is heat sensitive, processing temperature is of importance. In this study the effect of hot air drying temperature (40–70 °C) on the evolution of sulforaphane in cabbage during drying was investigated; outer leaves of cabbage, which are discarded and normally considered as waste, were used. The retention of sulforaphane in the finally dried DF powder was also determined. The results showed that the formation of sulforaphane occurred when the cabbage temperature during drying was in the range of 25–53.5 °C and thermal degradation took place once the cabbage temperature exceeded this range. A semi-empirical heat transfer and kinetic model was proposed to predict the evolution of sulforaphane during drying. Drying at 60 °C was suggested as an optimum condition to obtain the highest retention of sulforaphane in cabbage DF powder.