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Aims: The aim was to evaluate (i) the resistance of Escherichia coli BJ4 to citral in a buffer system as a function of citral concentration, treatment medium pH, storage time and initial inoculum size, (ii) the role of the sigma factor RpoS on citral resistance of E. coli, (iii) the role of the cell envelope damage in the mechanism of microbial inactivation by citral and (iiii) possible synergistic effects of mild heat treatment and pulsed electric fields (PEF) treatment combined with citral.

Methods and Results: The initial inoculum size greatly affected the efficacy of citral against E. coli cells. Exposure to 200 μl l⁻¹ of citral at pH 4·0 for 24 h at 20°C caused the inactivation of more than 5 log₁₀ cycles of cells starting at an inoculum size of 10⁶ or 10⁷ CFU ml⁻¹, whereas increasing the cell concentration to 10⁹ CFU ml⁻¹ caused <1 log₁₀ cycle of inactivation. Escherichia coli showed higher resistance to citral at pH …