1.2. Chemistry of garlic
Garlic bioactive compounds are placed into categories as: sulfurcontaining
and non-sulfur compounds. Sulphur is chiefly found as
alkylcysteine sulphoxides and gamma-glutamyl peptides which in
combination constitute more than 70% of the total sulphur content in
garlic. The degradation of alkyl cysteine sulphoxides, alliin, methiin,
and isoalliin is brought about by alliinase enzyme and result in a release
of powerful smelling volatiles, provide particular odor and flavor to the
Allium species. Alliin is converted into allicin by crushing the garlic
clove within seconds. Garlic remains odorless unless it is mashed.
Cross-section investigation has exhibited that location of the substrate
alliin and the enzyme alliinase are separate compartments. In garlic the
flavor precursor showing dominant characteristic is alliin having less
concentrations of isoalliin, methiin and trace amounts of propiin[17]. The
therapeutic effects of garlic are mainly attributed to a sulfur-containing
compound known as allicin[18]. The garlic clove lack allicin content but
contains its precursor, the non-protein amino acid alliin. Garlic bulbs
contain alliin and alliinase at about 1.7 and 2.8% of their dry weight,
respectively. By the crushing of garlic bulbs variable amounts of allicin
is produced ranging from 1.6-13.0% of their dry mass[19]