Supercritical fluid (SF) extracts of homogenized garlic (Allium sativum L.), ramp (A. tricoccum Ait.), and onion (A. cepa) were characterized with liquid chromatography (LC) and atmospheric pressure chemical ionization mass spectrometric identification. The major thiosulfinates from garlic and ramp were readily characterized by this technique. Small quantities of ajoene, a potent antithrombotic agent, were also found in SF extracts of garlic homogenates. The profiles of onion juice extracts revealed the usual thiosulfinates, zwiebelanes, and bissulfine reported in prior studies, as well as cepaenes previously identified in extracts of onion juice through extensive isolation steps and spectroscopic methods. The presence of trace quantities of allyl compounds in onion juice and propyl compounds in garlic and ramp homogenates has been verified by LC−mass spectrometry (MS). The presence of these compounds was not readily evident in previous analyses using gas chromatography−MS with cold-on-column injection and reversed-phase or normal phase LC with UV detection. Keywords: Supercritical fluid extraction; liquid chromatography; mass spectrometry; LC−MS; onion, Allium cepa; garlic, Allium sativum L.; ramp, Allium tricoccum Ait.; thiosulfinates

Supercritical fluid (SF) extracts of fresh garlic (Allium sativum) and fresh onion (Allium cepa) were analyzed by liquid chromatography, gas chromatography (GC), and mass spectrometry (MS). Allicin (2-propene-l-sulfinothioic acid S-2-propenyl ester), the major thiosulfinate found in fresh garlic, was readily extracted by using supercritical CO2 (SC-CO2). Under SF extraction conditions using a solvent trap, the yield of allicin from a water homogenate of fresh garlic was 98.2 %; however, when a solid-phase trap (i.e., condensation on glass beads) was used, the yield of allicin was 124.6% relative to yields obtained with methylene chloride extraction. An increase in the quantity of thermal decomposition products with respect to allicin was evident when the garlic was extracted at temperatures greater than 36 °C. The identity of allicin in the garlic SF extracts was confirmed by thermospray MS. The SF extraction of yellow onion was ca. 69% as efficient as the extraction with diethyl ether, as determined by GC-MS.

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Although a growing number of epidemiological studies indicate that dietary beta-carotene has anticarcinogenic activity, the mechanism(s) of beta-carotene protection remains to be definitively established. In this context, in vitro studies of beta-carotene have been, and continue to be, valuable. We examined the following critical features in designing an in vitro system for studying the protection action of beta-carotene: 1) form of beta-carotene used for cellular uptake, 2) cellular metabolism of beta-carotene, and 3) subcellular distribution of beta-carotene. It was determined that beta-carotene added to medium in a water-dispersible formulation is readily taken up by BALB/c 3T3 cells and is located predominantly in cellular membranes. Cellular uptake of beta-carotene added to medium in an organic solvent is greatly reduced. It was also found that intracellular retinol increased significantly after a three-day exposure of BALB/c 3T3 cells to media containing beta-carotene. This result suggests that the ability to metabolize beta-carotene to retinoids is not limited to cells of intestinal origin. The results and methodology described here will be useful in the rational design of in vitro assays for elucidating the mechanism(s) of beta-carotene protective effects at the cellular level.