Characterization of the Formation of Allicin and Other Thiosulfinates from Garlic

 

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Abstract

The effects of pH, neutralization after acidification, time, and temperature on the yield of dialkyl thiosulfinates released from garlic powder and garlic cloves were determined. All dipropenyl thiosulfinates (allicin, 1-propenyl allyl, and allyl 1-propenyl) were formed at an optimum pH of 4.5-5.0. The methyl propenyl thiosulfinates (allyl methyl + methyl allyl and 1-propenyl methyl + methyl 1-propenyl) and dimethyl thiosulfinate were optimally formed at pH 6.5-7.0 and pH 5.5, respectively. Below pH 3.6 no thiosulfinates were formed. Neutralization of the pH failed to restore thiosulfinate generation from garlic previously incubated at pH 3 or below. Thus, alliinase is completely and irreversibly inhibited by the acidic conditions found in the stomach. The dipropenyl thiosulfinates were completely formed in 0.3 min at 37°C, while the methyl thiosulfinates were not completely formed until 3.5 min. Allyl 1-propenyl thiosulfinate was the most rapidly formed, and the most unstable, thiosulfinate. The stability of the dipropenyl thiosulfinates was improved at pH 4.5 or lower. Drying garlic at 60°C had no effect on alliin or the rate of formation of the dipropenyl thiosulfinates, but decreased trans-1-propenylcysteine sulfoxide (isoalliin) and the rate of formation of the methyl thiosulfinates. The results demonstrate that there are two alliinase activities in garlic, that a stomach acid-resistant coating on garlic powder tablets is necessary for thiosulfinate release, and that carefully prepared garlic powder can release similar amounts of total thiosulfinates to whole garlic cloves.