Allicin Bioavailability from Alliinase-Inhibited Garlic

Allyl thiosulfinates (75% allicin) are responsible for most of the known health benefits of crushed raw garlic. Absent in garlic cloves, they are rapidly produced from alliin when endogenous alliinase is activated by crushing the cloves. The alliinase-dependent production of allyl thiosulfinates (hereafter called allicin) is known to be completely inhibited by heat and acid (pH ≤ 3.5) in vitro, bringing into question any allicin-related health benefits of cooked garlic or garlic powder supplements not protected from gastric acid. Indeed, most supplement brands have been shown to produce little allicin under USP/NF-defined simulated gastrointestinal conditions. To determine if allicin production in the human body might be different from in vitro predictions, a method for measuring allicin bioavailability was developed (breath AUC of its main metabolite, allyl methyl sulfide) and applied to heat-inactivated and acid-inactivated garlic. Allicin bioavailability from the alliin of boiled garlic was found to be 18% (14–25%), much higher than expected, with a similar result for garlic powder suspended in 1 N HCl (pH 0.6). When garlic powder was consumed in capsules with a low protein meal (expected gastric pH < 3), 34% of the alliin was converted to allicin, indicating that the local pH is increased by the dissolving capsule. When pure alliin was consumed, only 4% of it was converted to allicin, probably by intestinal bacteria. The substantial difference in allicin bioavailability between heat- or acid-inactivated garlic (18%) and pure alliin (4%) indicates that the body has the ability to partially reactivate inactive alliinase. This work has important implications: (1) the health benefits of raw garlic can be obtained with cooked garlic, if consumed in larger amounts, as is often the case, and (2) allicin bioavailability from garlic powder supplements may be considerably higher than predicted in vitro, depending on how they are made and consumed.