Phenolic compounds antimicrobial activity

Food Phenolic Compounds Antimicrobial Activity and Microbial Responses... 

Some phenolic acids such as ellagic acid can be used as floral markers of heather honey (Cherchi et al., 1994 Ferreres et al., 1996a,b), and the hydroxyciimamates (caffeic, p-coumaric, and ferulic acids) as floral markers of chestnut honey (Cherchi et al., 1994). Pinocembrin, pinobanksin, and chrysin are the characteristic flavonoids of propolis, and these flavo-noid compounds have been found in most European honey samples (Tomas-Barberan et al., 2001). However, for lavender and acacia honeys, no specific phenolic compoimds could be used as suitable floral markers (Tomas-Barberan et al., 2001). Other potential phytochemical markers like abscisic acid may become floral markers in heather honey (Cherchi et al., 1994). Abscisic acid was also detected in rapeseed, lime, and acacia honey samples (Tomas-Barberan et al., 2001). Snow and Manley-Harris (2004) studied antimicrobial activity of phenolics. 

Pereira JA, Pereira APG, Ferreira ICFR, Valentao P, Andrade PB, Seabra R, Estevinho L and Bento A. 2006. Table olives from Portugal phenolic compounds, antioxidant potential, and antimicrobial activity. J Agric Food Chem 54(22) 8425-8431. 

Due to the antimicrobial activity of many of the phenolic compounds against different bacterial and fungal strains, several reports about the antibacterial effects of C-glycosylfla-vones have appeared. 

Randhir R, Lin Y-T, Shetty K. 2004. Stimulation of phenolic compounds, antioxidant and antimicrobial activities in dark germinated mung bean sprouts in response to peptide and phytochemical elicitors. Process Biochem 39 637-646. 

Aromatic and phenolic compounds can mediate UV-protecting activities, which might be favorable for plants living in UV-rich environments, such as high altitudes [1[. Alkaloids (such as isoquinoline, quinoline, and indole alkaloids) that derive from aromatic amino acids, such as phenylalanine, tyrosine, and tryptophan, may have UV-absorbing properties, besides antiherbivoral and antimicrobial activities. 

Secondary compounds known for their antimicrobial activity include many phenolics (e.g., flavonoids, isoflavones, and simple phenolics), glu-cosinolates, nonproteinogenic amino acids, cyanogenic glycosides, acids, aldehydes, saponins, triterpenes, mono- and disesquiterpenes, and last but not least, alkaloids (4,17,42,149,312). 

Vivas et al. 1997). Recently, the evaluation of the dual antioxidant and antibacterial activity of 21 phenolic compounds mainly present in Vitis Vinifera L. belonging to different groups was examined (Garcfa-Ruiz et al. 2008b). Structure-activity relationships were probed for both antimicrobial and antioxidant properties of wine phenolics, confirming the potential of these compounds as an alternative to sulphites in winemaking. 

Antioxidant preservative by terminating free radicals formed during autoxidation of unsaturated lipids. It also possesses antimicrobial activity as a phenolic compound. 

The degree of ionization of acidic and basic antimicrobial agents depends on pH. Some compounds are active only in the unionized state (e.g., phenolics) whereas others are preferentially active as either the anion or cation. It therefore follows that the activity of a particular concentration of an agent will be enhanced at a pH that favors the formation of the active species. Thus, cationic antibacterials such as acridines and quaternary ammonium compounds are more active under alkaline conditions. Conversely, phenols and benzoic acid are more active in an acid medium. Chlorbutol is less active above pH 5 and unstable above pH 6. Phenylmercuric nitrate is only active at above pH 6 whereas thiomersal is more active under acid conditions. The sporicidal activity of glutaraldehyde is considerably enhanced under alkaline conditions whereas hypochlorites are virtually ineffective at above pH 8. 

Other antimicrobial phenolic compounds from the Anthemideae tribe are coumarins, which are derivatives of benzo-a-pyrone. Feresin et al. [199] isolated eight / -coumaric acid derivatives from the Argentinian medicinal plant Baccharis grisebachii. Two of them, 3-prenyl-/ -coumaric acid, Fig. (38) and 3,5-diprenyl-p-coumaric acid were active towards Epidermophyton floccosum and Trichophyton rubrum, with MIC values of 50 and 100-125 ig/ml, respectively. 

The occurrence in the olive pomace of unique oleuropein oligomers (14) with a degree of polymerization of up to five oleuropein monomers was reported by Cardoso et al. [27]. Their bioactivities have, however, not yet been studied. In fact, besides the evidence that olive phenolic compounds can have antioxidant, cardioprotective, antimicrobial, antihypertensive, anti-inflammatory, and chemo-preventive properties [26], the majority of the studies have focused on hydroxytyrosol (15). This compound has revealed remarkable pharmacological and antioxidant activities and thus has been further studied for its bioavaUability and metabolism in humans in order to establish its health-beneficial effects [29-31]. 

Among the compounds previously described, some of them showed antimicrobial activity. All the active compounds belong to the quinone methide-type. A phenolic compound isolated by Ankli and coworkers and not previously discussed (100), Fig. (56), was also tested, but it showed very low activity. 

In vitro, there has been observed the possible antimicrobial activity of oleuropein against human pathogenic bacteria. Moreover, the phenolic compound also confirmed its action on gram-positive and gram-negative bacterial strains such as Salmonella spp., Vibrio spp. and Staphylococcus aureus [91]. Experimental data indicated that M. pneumoniae, M hominis, M fermentans and M pirum are vulnerable to oleuropein [92]. 

From the cinnamic acids or phenyl propanoids described above, / -oxidation and truncation of side chains yields a variety of benzoic or simple phenolic acids [28], Rao et al., [22] identified gallic acid (18), gentisic acid (19), protocatechuic acid (20), />-hydroxybenzoic acid (21), oc-resorcyclic acid (22), vanillic acid (23) and salicylic acid (24) in C. arietinum and showed that overall, leaf content of all phenolic compounds was much greater than in roots and stem. They postulated that the production of these compounds may enhance the activity of indole acetic acid oxidase or may express antimicrobial properties when leached into the soil. However, Singh et al. [24] showed that the production of both 18 and 24 by C. arietinum was induced when treated by the culture filtrate of Sclerotium rolfsii along with the phenyl propanoids 14, 15 and 17 mentioned above. 

In order to explain and confirm the biological activities claimed by the traditional medicine, and to search for new biologically active compounds we studied the antimicrobial, antioxidative, immunomodulatory, antiinflammatory, skin-regenerating and antiviral properties of Fraxinus ornus bark extract and its components. In a parallel detailed phytochemical investigation of the extract we isolated and determined the structures of many hydroxycoumarins, secoiridoid glucosides, caffeoyl esters of phenylethanoid glycosides, lignans and other phenolic compounds. 

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