Antibacterial activity of heated garlic extract
The antibacterial activity of heated garlic against S. aureus
was tested in TSB containing different concentrations of garlic
extract heated (Extract 1) at 121 °C for different periods of
time (0 to 120 min) at 15 min intervals (Figure 2).
TSB with 15% blanched but not heated garlic extract was
not antibacterial at all against S. aureus and supported a
good growth of the bacterium (Log CFU/mL = 9.18; Figure 2)
as TSB itself and TSB with water replacing blanched garlic
extract supported growth to 9.23 and 9.15 Log CFU/mL, respectively.
The antibacterial activity of heated garlic progressively
increased towards 45 min of heating. Garlic extract at a
concentration of 15% heated for 45 min was completely bacteriostatic
for S. aureus for 24 h. However, the activity progressively
decreased as heating time was increased further.
Since the extract of blanched garlic (0 min heating) showed
no inhibition (Figure 2), the compounds with antibacterial
activity must have been newly formed from garlic
constituent(s) by heating and accumulated up until 45 min of
heating. From then on, the generation of the antibacterial
compound(s) was outpaced by their destruction. The extract
heated for 120 min retained some antibacterial activity and
the final cell number was smaller than that obtained in the
presence of the extract of blanched garlic. Alliin is reported
not to be antimicrobial unless reacted by the enzyme alliinase
(Brown and others 1954; Stoll and Seebeck 1951). The
boiled garlic extract of Cellini and others (1996) was antimicrobial
because they boiled the garlic extract after the garlic
was crushed, so that the alliinase enzyme had an opportunity
to react with its substrate. Therefore, the antimicrobial activity
of boiled garlic extract must be the residual antimicrobial
activity after boiling destroys most of the activity.
The antimicrobial activity of the extract (Extract 1) of
heated whole garlic was compared with that of garlic extracts
(Extract 2) heated after they were maintained at 37 °C
overnight to exhaust alliin (Table 1). This whole extract
showed some antibacterial activity, inhibiting bacterial
growth completely at 45%. This activity is similar to that