Premium
Inactivation of Escherichia coli by citral
Author(s) -
Somolinos M.,
García D.,
Condón S.,
Mackey B.,
Pagán R.
Publication year - 2010
Publication title -
journal of applied microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.889
H-Index - 156
eISSN - 1365-2672
pISSN - 1364-5072
DOI - 10.1111/j.1365-2672.2009.04597.x
Subject(s) - citral , rpos , escherichia coli , microbiology and biotechnology , chemistry , food science , biology , biochemistry , essential oil , gene expression , gene , promoter
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 log 10 cycles of cells starting at an inoculum size of 10 6 or 10 7 CFU ml −1 , whereas increasing the cell concentration to 10 9 CFU ml −1 caused <1 log 10 cycle of inactivation. Escherichia coli showed higher resistance to citral at pH 4·0 than pH 7·0. The rpo S null mutant strain E. coli BJ4L1 was less resistant to citral than the wild‐type strain. Occurrence of sublethal injury to both the cytoplasmic and outer membranes was demonstrated by adding sodium chloride or bile salts to the recovery media. The majority of sublethally injured cells by citral required energy and lipid synthesis for repair. A strongly synergistic lethal effect was shown by mild heat treatment combined with citral but the presence of citral during the application of a PEF treatment did not show any advantage. Conclusions: This work confirms that cell envelope damage is an important event in citral inactivation of bacteria, and it describes the key factors on the inactivation of E. coli cells by citral. Significance and Impact of the Study: Knowledge about the mechanism of microbial inactivation by citral helps establish successful combined preservation treatments.