Effect of PEF on microbial inactivation and physical–chemical properties of green tea extracts

The effects of pulsed electric fields (PEF) on (1) the inactivation of Escherichia coli and Staphylococus aureus in green tea beverage, and (2) the color, green tea polyphenols (GTP) content, and total free amino acids in green tea extracts were investigated. Green tea extract samples inoculated with E. coli and S. aureus were treated using a bench-scale PEF system at electric field strengths of 18.1, 27.4, and 38.4 kV/cm and total treatment times of 40, 80, 120, 160 and 200 μs. The inactivation of E. coli and S. aureus by PEF treatment at 38.4 kV/cm for 160 and 200 μs reached 5.6 and 4.9 log reductions, respectively. PEF processing caused no considerable changes in color, GTP and total free amino acids. The storage tests at 4 °C showed that synergistic effect of low temperature storage and the antimicrobial functionality of GTP resulted in a considerable reduction in the microoganisms of the PEF-treated tea beverage, extending its shelf-life to over 6 months at 4 °C.