The effect of chewing on oral glucoraphanin hydrolysis in raw and steamed broccoli

Chewing disrupts broccoli cells, and myrosinase can effectively hydrolyze the glucosinolate glucoraphanin into the biological active sulforaphane. The influence of chewing time and steaming time on glucoraphanin hydrolysis as well as sulforaphane and sulforaphane nitrile formation in broccoli was studied. To study the effect of chewing time on differently steamed broccoli, broccoli was chewed for 11 s, 22 s, 30 s and 40 s by volunteers. To determine the effect of steaming time, raw and steamed broccoli samples were chewed for 22 s. Glucoraphanin, sulforaphane and sulforaphane nitrile were analyzed in all samples. Longer chewing times of raw, 0.5-min and 1-min steamed broccoli, which contained active myrosinase, lead to a higher hydrolysis. The highest hydrolysis rate of glucoraphanin was found in 0.5-min steamed broccoli (38%) and 2-min steamed samples which contained the highest sulforaphane concentration. This could lead to a recommendation to steam broccoli for a short time before consumption.