158 Handbook of herbs and spices
gallocatechin gallate in green tea catechins inhibited extracellular release of
verocytotoxin from E. coli O157:H7 (Sugita-Konishi et al., 1999). Moreover Ahn et
al. (1991), testing the polyphenols of Thea sinensis against Cl. perfringens and Cl.
difficile, found that the gallate moiety of polyphenols seems to be required for growth
inhibiting activity.
Phenolic extracts of berries containing ellagitannins, anthocyanins, hydroxycinnamic
acids and flavonols, lignans were inhibitory to intestinal Gram (–) pathogens Salmonella,
E. coli, Staphylococcus aureus (Puupponen-Pimia et al., 2001, 2005). Ellagitannins
(esters of hexahydroxydiphenic acid, which is a dimeric derivative of gallic acid and
a polyol, glucose or quinic acid) were shown to be strong inhibitory compounds on
St. aureus. Phenolic compounds were only partially responsible for the growth inhibition
of Salmonella and most of the antimicrobial effects probably originate from other
compounds such as organic acids, citric, malic, benzoic acid (Puupponen-Pimia et
al., 2005). Wen et al., (2003) reported that phenolic acids such as hydroxycinnamic
acids, exhibited antibacterial activity against several strains of L. monocytogenes.
Tannins have been reported in general to be bacteriostatic and/or bactericidal for
many disease-associated bacteria (Toda et al., 1989; Scalbert, 1991; Hussein et al.,
1997; Chung et al., 1993; Cowan, 1999; Djipa et al., 2000). Chung et al., (1993)
demonstrated also that inhibitory effects against a variety of foodborne bacteria, such
as St. aureus, S. enteritidis, S. paratyphi and E. coli were associated with the ester
linkage between gallic acid and polyols. Punica granatum also possesses high amount
of tannins.
The seco-tanapartholides A and B, active constituents of the Artemisia princeps
var. orientalis, produced a clear inhibitory effect on human intestinal bacteria C.
perfringens, Bacteroides fragilis and Staph. aureus without any adverse effects on
lactic-acid producing bacteria (Cho et al., 2003).
The antibacterial activities of catechins were predominantly related to the gallic
acid moiety and the number of hydroxyl groups. It has also been reported that catechins
damage the membrane lipid layer (Ikigai et al., 1993). Catechins probably damage
the membrane of H. pylori and epigallocatechin gallate inhibits the urease activity
and motility of H. pylori which may contribute to its antibacterial activity in vivo
(Mabe et al., 1999). Catechins act bactericidally at high pH while essential oils may
show antibacterial activity in the stomach because they are more effective at lower
pH (Ohno et al., 2003).
Different mechanisms of action proposed to explain tannin antimicrobial activity
including inhibition of extracellular microbial enzymes, deprivation of the substrates
required for microbial growth or direct action on microbial metabolism through
inhibition of oxidative phosphorylation. Complexation of metal ions by tannins could
also be a possible mechanism (Scalbert, 1991).
The antibacterial properties of cranberry may be associated with inhibition of E.
coli adherence to mucosal surfaces by cranberry juice (Schmidt and Sobota, 1988).
It has been suggested that proanthocyanidins (condensed tannins) are responsible for
this anti-adhesion property (Howell, 2002; Howell et al., 1998). Studies with mice
fed with cranberry proanthocyanidins showed that properties of the urine may be
altered by the proanthocyanidins in such a way that adhesion is inhibited (Howell et
al., 2001). Another hypothesis is that metabolites of proanthocyanidins could act on
the colonic bacterial receptors making them incapable of binding to the uroepithelium
and proliferate (Harmand and Blanquet, 1978). Burger et al. (2002) reported that a
high molecular weight constituent of cranberry juice inhibited adhesion of Helicobacter