C. cassia oil can inhibit the growth of non-O157 STECs at concentration as low as 0.025% (v/v).
Cinnamomum cassia, a spice in cuisine, was tested for its antibacterial efficacy on non-O157 STECs including O26, O45, O103, O111, O121, O145.
Non-O157 STEC interventions have included lactic acid wash and acidified sodium chlorite, peroxyacetic acid, and sodium metasilicate.
However, it is volatile and poorly water soluble, which adds to the difficulty to apply directly into food and incorporate into edible films and coatings.
Aroma attributes are another factor limiting sensory acceptance of food products with the substance, said the researchers.
Bacteria were routinely grown in Luria Broth (LB) at 37 °C with aeration.
As low as 5μL of 4% (v/v) C. cassia oil per disc inhibited the growth of all tested non-O157 STECs with inhibition zones around 8-9 mm.
Inhibitory effects strengthened with increasing amount of C. cassia oil per disc, said the researchers.
The disk diffusion assay indicated that 20μL 4% (v/v) C. cassia oil per disk resulted in inhibition zones of 15 mm, 18.5 mm, 15.7 mm, 19.3 mm, 18.8 mm, and 25.3 mm for O26:H11, O45:NM, O103:H2, O111:H2, O121:H19, and O145:NT, respectively.
Gas chromatography-mass spectrometry (GC/MS) analysis showed that the major component of C. cassia oil was cinnamaldehyde (59.96%).
Concentration, population and strain dependent
Inhibitory effect on the growth of non-O157 STECs is concentration, population and strain dependent, said the researchers.
At the low inoculation population (∼2.5 x 105 CFU/mL) including 0.00625% (v/v) of C. cassia oil increased the lag phase of all tested non-O157 STECs except O121:H19 for about one hour.
At the concentration of 0.0125% (v/v), C. cassia oil delayed the log phase of O45:NM, O103:H2, O111:H2, and O121:H19 for about five hours, while O26:H11 and O145:NT for about 10 hours.
C. cassia oil at the concentration of 0.01875% (v/v) inhibited the growth of O26:H11 and O145:NT for up to 24 hours, and increased the duration of lag phase of O45:NM, O103:H2, O111:H2, O121:H19 by 18, 12, six, and 16 hours, respectively.
C. cassia oil completely inhibited the growth of all tested non-O157 STECs for at least 24 hours.
At the high inoculation population (∼5 × 106 CFU/mL), C. cassia oil was less effective, said the researchers.
C. cassia oil at 0.00625% or 0.0125% (v/v) had limited efficacy in inhibiting the growth of all test non-O157 STECs.
Including 0.01875% (v/v) C. cassia oil delayed the log phase of O45:NM, O103:H2, O111:H2, and O121:H19 for about three hours, and O26:H11, O145:NT for eight and 10 hours, respectively.
Including 0.01875% (v/v) it decreased the stationary phase population of O26:H11, O45:NM, O103:H2, and O121:H19.
C. cassia oil at 0.025% (v/v) inhibited the growth of O121:H19 and O145:NT for at least 24 hours and elongated the duration of lag phase of O45:NM, O103:H2, and O111:H2 for less than eight hours and O26:H11 for less than 14 hours.
The US Department of Agriculture Food Safety and Inspection Service has a “zero tolerance” policy for the Centers for Disease Control and Prevention (CDC) top six non-O157 STECs in raw ground beef and trimmings, so any raw non-intact beef products containing these pathogens are adulterated.
Source: Food Control, Volume 46, December 2014, Pages 374–381
Online ahead of print, DOI:10.1016/j.foodcont.2014.05.050
“Inhibitory effect of Cinnamomum cassia oil on non-O157 Shiga toxin-producing Escherichia coli”
Authors: Lina Sheng, Mei-Jun Zhu