Location: Vegetable ResearchTitle: Impact of thermal processing on sulforaphane yield from broccoli (Brassica oleracea L. var. italica)) Author
Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2012
Publication Date: 7/1/2012
Citation: Wang, G., Farnham, M.W., Jeffery, E. 2012. Impact of thermal processing on sulforaphane yield from broccoli (Brassica oleracea L. var. italica). Journal of Agricultural and Food Chemistry. 60:6743-6748. Interpretive Summary: Broccoli florets contain a chemical constituent called glucoraphanin that breaks down to a product called sulforaphane when the vegetable is cooked or eaten. Sulforaphane has been found to confer a health benefit when consumed by people, possibly protecting them from certain kinds of cancer. Depending on how the vegetable is cooked, it may contain more or less sulforaphane because some is destroyed during cooking. It this study an ARS scientist at the U.S. Vegetable Laboratory in Charleston, SC, cooperated with scientists at the University of Illinois at Champaign to determine what the effects of different cooking methods including boiling, steaming and microwaving had on the final content of sulforaphane in broccoli following cooking. Broccoli heads harvested from different field-grown hybrid varieties were also tested to determine the effect of variety on sulforaphane content. The amount of sulforaphane after cooking varied depending on the variety tested. In addition, steam cooking resulted in the highest concentration of sulforaphane compared to all other cooking treatments. This information is important for making cooking recommendations to food technologists and consumers so that preparation of cooked broccoli for eating will result in a vegetable with the highest health promoting potential possible.
Technical Abstract: In broccoli, sulforaphane forms when the glucosinolate glucoraphanin is hydrolyzed by the endogenous plant thiohydrolase myrosinase. A myrosinase cofactor directs hydrolysis away from formation of bioactive sulforaphane and toward an inactive product, sulforaphane nitrile. The cofactor is more heat sensitive than myrosinase, presenting an opportunity to preferentially direct hydrolysis toward sulforaphane formation, through regulation of thermal processing. Four broccoli cultivars were microwave heated, boiled, or steamed for varying lengths of time. Production of nitrile during hydrolysis of unheated broccoli varied among cultivars from 91 to 52% of hydrolysis products (Pinnacle > Marathon > Patriot > Brigadier). Boiling and microwave heating caused an initial loss of nitrile, with a concomitant increase in sulforaphane, followed by loss of sulforaphane, all within one minute. In contrast, steaming enhanced sulforaphane yield between 1.0 and 3.0 min in all but Brigadier. We conclude that steaming for 1.0 – 3.0 min provides optimal sulforaphane yield from a broccoli meal.