Antimicrobial activities of sulfur compounds derived from S-alk(en)yl-L-cysteine sulfoxides in Allium and Brassica

Allium and Brassica vegetables have long been known for their antimicrobial activity against various microorganisms, including Gram-positive and Gram- negative bacteria and fungi. Most microorganisms tested were sensitive to e xtracts of the Allium and Brassica vegetables and the degree of sensitivity varied depending on the strain under study and test conditions. Among the vegetables, garlic showed the most potent activity, followed by onion. Bras sica, including cabbage, showed the least potent activity. The principal an timicrobial compounds of Allium and Brassica have been elucidated as allici n (S-allyl-L-propenethiosulfinate) and methyl methanethiosulfinate, respect ively. Both compounds belong to the same chemical group, thiosulfinate, gen erated from S-allyl and S-methyl derivatives of L-cysteine sulfoxide, respe ctively, existing in Allium and Brassica as major non-protein sulfur-contai ning amino acids. There have been only few applications of garlic as a natu ral food preservative, in spite of numerous studies on antimicrobial activi ty of the vegetables. Relative instability of the antimicrobial compounds a nd the strong odor of their mother plants seem to limit the use of them as a practical food preservative.