The present study was undertaken to characterize the antibacterial activity of the aqueous extracts (AEs)obtained from the leaves of Borago officinalis L. and Brassica juncea L. The antagonistic activity wasevaluated against several bacteria (42 strains of Listeria monocytogenes, 35 strains of Staphylococcusaureus, 38 strains of Enterobacter spp. and 18 strains of Salmonella enterica) commonly associated withfoodborne diseases by paper disc diffusion method. The susceptibility to the plant extracts was strainspecific. Thirty-five strains (7 L. monocytogenes, 11 S. aureus, 1 S. Enteritidis, 1 S. Veneziana, 7 Enterobacterhormaechei, 5 Enterobacter cloacae, 1 Enterobacter sakazakii and 2 Enterobacter amnigenus) were sensitiveto both AEs. The activity of B. juncea AE towards the Gram-positive strains was generally higher than thatobserved for B. officinalis (45 and 22 strains inhibited by B. juncea and B. officinalis, respectively), while anopposite trend was registered against the Gram-negative strains (22 and 35 strains inhibited by B. junceaand B. officinalis, respectively). The highest inhibition was displayed by B. juncea AE against E. sakazakii23A. B. officinalis AE showed the same minimum inhibitory concentration (MIC) (10 mg/mL) for themajority of the most sensitive strains, while the MIC of B. juncea AE was different for each bacterialspecies and the lowest concentration was registered to inhibit enterobacteria (3.1 mg/mL). After 1-yearstorage in different thermal conditions (room temperature, 4 C and 20 C), both AEs lost theirinhibitory power. The extracts did not show cellular toxicity when tested against sheep erythrocytes.Hence, B. officinalis and B. juncea AEs were effective as natural antibacterial substances. AEs were testedin situ in three food model systems (meat, fish and vegetable) at two concentrations, but only whenadded at a concentration 10-fold higher than that showing definite efficacy in vitro (100 and 31 mg/mLfor B. officinalis and B. juncea, respectively), they inhibited the growth of the sensitive strains, eventhough the cells were still viable after 24 h. The influence of AEs on the volatile organic compounds(VOCs) composition of the food models was analysed by gas chromatography/mass spectrometry. Thedifferent levels of alcohols, aldehydes, esters, hydrocarbons, ketones and phenol registered, showed aconsistent effect of B. officinalis and B. juncea AEs on the VOCs of the food models. However, the sniffingassay found only B. juncea AE impacting consistently the final aroma of the food models.
|Numero di pagine||8|
|Stato di pubblicazione||Published - 2014|
All Science Journal Classification (ASJC) codes
- Food Science