Biological an chemical stability

J. Agric. Food Chem. 2008, 56, 4229–4235

4229

Biological and Chemical Stability of Garlic-Derived Allicin
HIROYUKI FUJISAWA,§,# KAORU SUMA,† KANA ORIGUCHI,† HITOMI KUMAGAI,§,† TAIICHIRO SEKI,§,† AND TOYOHIKO ARIGA§,†,*
Nihon University Graduate School of Applied Life Sciences, 1866 Kameino, Fujisawa 252-8510, Japan; Nagaoka Perfumery Company, Ltd., 2-2-6 Kitakyuhoujimachi, Chuo-ku, Osaka,541-0057, Japan; and Department of Agricultural and Biological Chemistry, College of Bioresource Sciences, Nihon University, 1866 Kameino, Fujisawa 252-8510, Japan

This study verifies the instability of garlic (Allium sativum L.)-derived allyl 2-propenylthiosulfinate (allicin) in various aqueous and ethanolic solutions as well as in vegetable oil through chemical and biological analysesperformed simultaneously. Crushed fresh garlic cloves generated antibacterial activity and chemically detectable allicin, a major antibacterial principle, and both declined on a daily basis in aqueous and ethanolic solutions at room temperature, showing biological and chemical half-lives of about 6 and 11 days, respectively. Allicin was more stable in 20% alcohol than in water, but surprisingly unstablein vegetable oil, with an activity half-life 0.8 h, as estimated from its antibacterial activity toward Escherichia coli, and a chemical half-life of 3.1 h, based on chromatographic quantification. In alcoholic and aqueous extracts, the biological half-life of allicin tended to be longer than the chemical one, suggesting the occurrence of bioactive compounds other than allicin in the extracts.KEYWORDS: Allicin; garlic; stability; antibacterial activity; Staphylococcus aureus; Escherichia coli

INTRODUCTION

Garlic (Allium satiVum L.) has long been used as one of the representative vegetables possessing marked pharmacological potentials, such as antimicrobial activity (1, 2) and antiplatelet and antithrombotic activities (3–7) as well as anticancer activity (8–10). Studies on garlichave been reported in more than 3000 papers, which have disclosed that garlic produces many organosulfur compounds depending on the method of cooking, treatment, or preservation (11–13); these differences result in differences in its biological effects. Because crushed fresh garlic exhibits strong antimicrobial activity, people use garlic as an indispensable plant to preserve fresh meat as long aspossible (14, 15). Allicin is the most classic of the effective substances found in the garlic; hence, the potential of this plant has been assumed to be due to the allicin (16). However, through much scientific research, allicin has taken second place to its daughter components, alk(en)yl sulfides, which have been accepted as substances exhibiting most of garlic’s potential in vivo (13, 17). As oneof the decisive shortcomings of allicin, upon ingestion, allicin changes from its reactive form into stable sulfides in an intrastomach acidic solution or into breakdown products involving allyl methyl sulfides and, finally, into mercaptan, in vivo (18).
* Author to whom correspondence should be addressed [telephone (+81) 466-84-3948; fax (+81) 466-84-3949; e-mail ariga@ brs.nihon-u.ac.jp]. § NihonUniversity Graduate School. # Nagaoka Perfumery Co., Ltd. † Nihon University.

Recent studies on the anticancer effects of garlic have revealed that allicin can induce apoptosis in cancer cells through oxidative modification of cellular sulfhydryl (thiol) groups (19). Arditti et al. (20) and Miron et al. (21) reported that characteristic properties of allicin, such as high membrane permeabilityand congenital high reactivity, worked favorably in the tumor. These researchers have tried to generate allicin in situ to induce apoptosis of cancer cells in vivo. For this purpose, they delivered alliinase onto the cell surface as a conjugate with a cancer cellspecific antibody, and then alliin was injected into the bloodstream to produce allicin at the target site (20, 21). In their studies,...