To test how different preparation and cooking methods affected thiosulfinates, plant geneticist Philipp Simon, Ph.D., of the University of Wisconsin, Madison, and a group of researchers at Cuyo University in Argentina gathered four pounds of garlic and crushed half with a garlic press. They let all the garlic sit at room temperature for 10 minutes and then cooked batches of each sample in a 400-degree oven, in a microwave, or in boiling water for up to 20 minutes. Next, they tested whether each batch of garlic could alter how well blood platelets clumped. Garlic cooked whole had no anti-clumping ability, but crushed, lightly cooked garlic had a significant effect in reducing platelet clumping.
The reason: Thiosulfinates don’t form until the clove is crushed or cut.