Various components of garlic and aged garlic extract, including allicin, S-allylcysteine (SAC) and volatile metabolites of allicin were determined in breath, plasma and simulated gastric fluids by HPLC, gas chromatography (GC) or HPLC- and GC-mass spectrometry (MS). Data indicate that allicin decomposes in stomach acid to release allyl sulfides, disulfides and other volatiles that are postulated to be metabolized by glutathione and/or S-adenosylmethionine to form allyl methyl sulfide. SAC can be absorbed by the body and can be determined in plasma by HPLC or HPLC-MS using atmospheric pressure chemical ionization (APCI)-MS.
Gas Chromatography-Mass Spectrometry (GC-MS) was the major technique used to determine various metabolites after consumption of dehydrated granular garlic and an enteric-coated garlic preparation, in breath, plasma, and simulated gastric fluids. A special short-path thermal desorption device was used as an introduction technique for the gas chromatograph for the determination of volatiles. These garlic preparations release allicin, which decomposes in stomach acid or with time in the intestine to release allyl sulfides, disulfides and other volatiles, some of which are postulated to be metabolized by glutathione and/or S-adenosylmethionine to form allyl methyl sulfide, the main sulfur containing volatile metabolite. S-Allylcysteine, a non-volatile bioactive component of aged garlic preparations, was determined in human plasma and urine by HPLC-MS using the negative ion atmospheric pressure chemical ionization mode (APcI)- MS. The technique of selected ion monitoring was used for quantitation. A synthetic internal standard of deuterated S-allylcysteine was added to the plasma or urine to ensure recovery and to obtain reliable quantitative data.
Garlic-bome volatile compounds were monitored by breath analysis of human subjects in a time course study following the ingestion of various garlic samples. After specific time intervals, 1 to 1.2 liters of breath were purged and trapped through porous polymer resins and analyzed via short path thermal desorption GC-MS methodology. In addition, quantification was achieved by GC with flame ionization detection using an internal standard. Allyl methyl sulfide, diallyl sulfide, diallyl disulfide, p-cymene and D-limonene were found consistently in all subjects. Allyl thiol was detected occasionally. The individual appearance and elimination curves for these phytochemicals were found to differ, suggesting that experimental observations related to the pharmacokinetic behavior of the individual compounds. Hydrogen sulfide, a potential breath odor compound, was not efficiently trapped due to its low breakthrough volume in the adsorbent resins. Therefore, this compound was analyzed by direct injection of breath samples using sulfur sensitive flame photometric GC methodology. Preliminary evidence suggests that stomach acid caused increased evolution of this compound during digestion. The procedure described proved to be a useful noninvasive technique for measuring low levels of volatile food-borne phytochemicals on the breath of human subjects.
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