Total phenolic contents and antibacterial activities of grape (Vitis vinifera L.) extracts

Powdered grape seeds and bagasse were extracted with petroleum ether to remove fatty material and then re-extracted with different solvent mixtures to determine their total phenolics and antibacterial activities. In the grape seeds extracts the content of total phenolic compounds was found to be 627.98 mg gallic acid equivalent (GAE)/g with acetone:water:acetic acid (90:9.5:0.5) and 667.87 mg GAE/g with ethyl acetate:methanol:water (60:30:10). The bagasse extracts contained 45.44 mg GAE/g and 29.55 mg GAE/g with ethyl acetate:methanol:water (60:30:10) and ethanol:water (95:5), respectively. These extracts at 1%, 2%, 4% and 20% concentrations were tested for their antibacterial effects by using the paper disc diffusion method against some food spoilage and pathogenic bacteria including Aeromonas hydrophila ATCC 7965, Bacillus amyloliquefaciens ATCC 3842, Bacillus brevis FMC 3, Bacillus cereus FMC 19, Bacillus megaterium DSM 32, Bacillus subtilis IMG 22, Enterobacter aerogenes CCM 2531, Enterococcus feacalis ATCC 15753, Escherichia coli DM, Klebsiella pneumoniae FMC 5, Listeria monocytogenes Scott A, Mycobacterium smegmatis RUT, Proteus vulgaris FMC 1, Pseudomonas aeruginosa ATCC 27853 and Staphylococcus aureus COWAN 1. The grape seed extracts at 20% concentration inhibited all the bacteria except B. amyloliquefaciens. The acetone:water:acetic acid (90:9.5:0.5) extract was found to be more effective than the other one, whose extracts at 4% concentration were inactive against A. hydrophila, B. amyloliquefaciens, B. megaterium and B. subtilis, while the acetone:water:acetic acid (90:9.5:0.5) extract at 4% was effective against most of the test bacteria. The grape bagasse extracts and methanol (control) had no inhibitory effects on the fifteen bacteria tested. The grape seed extracts at 1% and 2% concentrations were also ineffective. Consequently, grape seed extracts at 4% and 20% may be useful as antibacterial agents to prevent the deterioration of food products.