Activité antimicrobienne des extraits phénoliques de caroube Ceratonia siliqua (L.)

Abstract

The goal of the present study is to explore the antimicrobial activity of phenolic carob pods extract (Ceratonia siliqua L.) against eight pathogenic strains (Bacillus cereus ATCC 11778, Bacillus cereus ATCC 14579, Staphylococcus aureus ATCC 25923, Staphylococcus aureus ATCC 33862, Escherichia coli ATCC 25922, Escherichia coli ATCC 8739, Shigella sonnei ATCC p4001, Pseudomonas aeruginosa ATCC 27853) and also its effect on survival of two beneficial strains (Lactobacillus rhamnosus LbRE-LSAS and Bifidobacterium animalis subsp lactis Bb12). Carob fruits were collected in Mostaganem area. Disk diffusion method was used for the determination of inhibition zone diameter and cell count was monitored during the whole exposure of the strains to the extract. Total polyphenols (Folin-Ciocalteu method) and total flavonoids (method of aluminum trichloride) were determined in the two carob extracts: ethanol-water extract (7v/3v) (EWPC) (23.79 mg/g) and aqueous extract (EAPC) (32.2 mg/g). Escherichia coli ATTC 25922 strain was the most sensitive strain toward the phenolic extract of carob pods followed by Escherichia coli ATCC 8739, Bacillus cereus ATCC 14579, Staphylococcus aureus ATCC 25923, Staphylococcus aureus ATCC 33862, Shigella sonnei ATCC p4001, and Bacillus cereus ATCC 11778, with an inhibition zone diameter ranging from 10 to 17 mm in the presence of 50 mg/mL carob aqueous phenolic extract. Beneficial strains (LbRE - LSAS and Bb12) growth was slightly improved compared to the control in the presence of the lowest phenolic extract concentration used (10 mg/mL), reaching 27% of maximal biomass improvement. In contrast, the higher phenolic extract concentrations (20 and 50 mg/mL) delay the growth of Lactobacillus rhamnosus strain LbRE-LSAS which is the more resistant strain to the inhibitory effect of polyphenols comparatively to Bb12 strain. These results may suggest that phenolic extract of carob could be used as a food preservative agent against a number of pathogens without any significant inhibition of beneficial or probiotic strains of digestive interest.