Enhancement of antimicrobial activity of white tea against Escherichia coli O157:H7 with a combination of lactic acid and copper

The objective of this study was to determine the efficacy of copper alone or in combination with lactic acid to enhance the antimicrobial activity of white tea extract against E. coli O157:H7 in a laboratory medium.  Batches of fresh Brain Heart Infusion Broth (BHI) were prepared and divided into two groups:   one batch to which we added 50mg/ml water extract white tea   and one batch treated without extract.   Each group was then divided into 10- 25 ml batches of the following treatments:  0, 5, 10, 20, and 40 ppm copper (Cu) alone or in combination with 0.1 and 0.2% lactic acid (La). The prepared samples were then sterilized at 121/15 min and allowed to cool to room temperature before being separately inoculated with 4 strains of E. coli O157:H7 at approximately 3 log CFU/ml.  Samples were incubated at 37°C for 8 hrs. Bacterial growth was determined by optical density (610 nm) at 2 hrs intervals after which the final bacterial count was determined.  Our results showed that white tea extract was able to reduce E. coli O157:H7 by 1 log CFU/ml.   The addition of 40 ppm copper and 0.2% lactic acid reduced the population by 3 log CFU. The combination of white tea extract with 20 ppm copper and 0.1% lactic acid reduced E. coli O157:H7 by 5 log CFU.  These results suggest that the use of low concentrations of lactic acid and copper can enhance the antimicrobial activity of white tea extract and reduce the risk of foodborne pathogens.