Herbs, spices and gut health 157
∑ The paper disc agar diffusion method with measurement of the radius or diameter
of the zone of inhibition of bacterial growth around paper discs impregnated with
(or wells containing) an antimicrobial compound on agar media.∑ Broth or Agar dilution assays with measurement of the inhibition of bacterial
growth in broth or agar medium.
∑ Agar or broth microdilution method and agar dilution method for MIC and
MBC.
∑ Measurement of changes in optical density or impedance in a liquid growth
medium containing the antimicrobial compound.
In vivo studies using animal models were conducted for the assessment of the inhibitory
activity of plant essential oils against H. pylori.
10.3.2 Mechanisms of action – active compounds
The antimicrobial activity of herbs and spices is attributed mainly to their phenolic
constituents and/or essential oil fraction (Table 10.3). Phenolics and polyphenols
could be simple phenolic acids, quinones, flavones, tannins and coumarins (Cowan,
1999). The phenolic compounds carvacrol and thymol present in the essential oil
from oregano and thyme exhibit considerable antimicrobial and antifungicidal activity
(Basilico and Basilico, 1999). Carvacrol, occuring in the volatile oils of black pepper,
clove, geranium, nutmeg, oregano and thyme has been found to be the component
with the widest spectrum of activity (Dorman and Deans, 2000). Phenols such as
thymol and carvacrol and their methyl ethers are also the main components of the
essential oil of Satureja montana (Skocibusic and Bezic, 2003).
Mainly responsible for the bactericidal action of the Japanese herb wasabi is the
component allyl isothiocyanate. This has been shown to inhibit Vibrio parahaemolyticus
(Hasegawa et al., 1999; Shin et al., 2004). Katsuhiro et al. (1999), reported catechins
as active compounds in teas with the epigallocatechin gallate of green tea being the
catechin with the strongest activity against H. pylori. Epigallocatechin gallate and
Table 10.3 Herbs, plants and spices and their active constituents
Herb/spice Active compound Herb/spice Active compound
Allspice eugenol, methyl eugenol Olive oleuropein
Berries ellagitannins, anthocyanins, Oregano thymol, carvacrol
hydroxycinnamic acids,
flavonols, lignans
Caraway carvone Pepper monoterpenes
Cinnamon cinnamaldehyde, eugenol Thyme thymol, carvacrol, menthol,
menthone
Clove eugenol, eugenol acetate Wasabi allyl isothiocyanate
Garlic diallyl disulphate, diallyl Artemisia seco-tanapartholides A and B
trisulphide, allyl propyl princeps var.
disulphide orientalis
Green tea epigallocatechin gallate, Punica granatum tannins
gallocatechin gallate
Mint a,b-pinene, limonene, Satureja montana thymol, carvacrol
1,8-cineole
Data from: Cho et al., (2003); Hasegawa et al., (1999); Nychas et al., (2003); Puupponen-Pimia et al., (2001,
2005); Shin et al., (2004); Skocibusic and Bezic, (2003); Sugita-Konishi et al., (1999).