[Studies on the stabilities of bioactive selenocompounds in selenium-enriched garlic and onion]

It is reported that selenium (Se) incorporation into garlic increases the bioactivities of garlic. Hence, the chemical changes of selenocompounds during processing and storage will influence the bioactive effectiveness of Se-enriched garlic. The principal selenocompounds in Se-enriched garlic are water-soluble, and several comparative experiments are thus conducted to examine the stabilities of the selenocompounds in water extracts of Se-enriched garlic and Se-enriched onion. The results show that preparing the garlic powder by freeze-drying technique can maintain the chemical properties of the selenium compounds in Se-enriched garlic. Se-methyl-selenocysteine is unstable in water extract of Se-enriched garlic when the extract is prepared and stored at room temperature. Specific alliinase inhibitor hydroxylamine (NHOH.HCl) effectively prevents the loss of Se-methyl-selenocysteine, which suggests that the decomposition of Se-methyl-selenocysteine may be catalyzed by alliinase. Se-methyl-selenocysteine is one of the main bioactive selenocompounds in Se-enriched garlic. The procedures of processing and storage should be carefully chosen to prevent the loss of selenocompounds and the decrease of the bioactivity of Se-enriched garlic. Se-enriched onion also contains alliinase and Se-methyl-selenocysteine, but its Se-methyl-selenocysteine is proved to be stable in the same water extract as that of Se-enriched garlic. The stability differences of Se-methyl-selenocysteine in Se-enriched garlic and onion, the mechanism of selenocompound decomposition and the bio-activities of decomposed compounds in Se-enriched garlic need to be further studied.