Antimicrobial properties of chesnut shell extract as an ecofriendly approach for food preservation

The chestnut industry generates large quantities of by-products, including the chestnut shell, which is a source of phenolic compounds. In this study, MIC (minimum inhibitory concentration) of chestnut shell extract was determined by the disk diffusion method. The chestnut shell was freeze-dried and milled. The extract was obtained by ultrasound assisted technique using water 70% : etanol 30% and subsequently lyophilized. Muller-Hinton plates were inoculated with ~10⁵ CFU/mL of Escherichia coli O157:H7 9001, Yersinia enterocolitica ATCC 9018, Staphylococcus aureus ATCC, Salmonella ATCC, Salmonella Typhimurium 14028, Enterococcus faecalis 19433, Enterococcus faecium 20477, wild Listeria monocytogenes ATCC 7973, Listeria ATCC 7644, Pseudomonas JI-Me-LM03 and Escherichia coli ATCC 1175. Sterile paper discs (6 mm) were placed on the inoculated culture medium and impregnated with 10 µL of each extract. Seven concentrations of extract between 0.3% and 2.1% were tested. The plates were incubated for 24h at 37ºC. The antibacterial efficacy of the extracts was indicated by a halo formed around the paper disk. The work was carried out in triplicate. Halos were found at 1.5%, 1.8% and 2.1% on Listeria ATCC 7973 (8.32±0.06 mm for 2.1%), Enterococcus faecalis 19433 (8.94 ±0.41 mm for 2.1%), and Staphylococcus aureus ATCC (10.26±0.19 mm at 2.1%). For the remaining microorganisms no halos were observed. The tested extract shows antimicrobial activity, showing promise for the control of pathogens in the food industry.