Inhibitory effects of sucrose monolaurate, alone and in combination with organic acids, on Listeria monocytogenes and Staphylococcus aureus.

The effects of sucrose esters of fatty acids, alone and in combination with ethylenediaminetetraacetic acid (EDTA), acetic acid, lactic acid and citric acid, on survival, growth and thermal inactivation of Listeria monocytogenes and Staphylococcus aureus were determined. The presence of sucrose monocaprate (400 micrograms ml-1) in tryptose phosphate broth (TPB) or tryptic soy broth (TSB) did not inhibit the growth of L. monocytogenes or Staph. aureus, respectively. However, significantly (P < or = 0.05) lower populations of L. monocytogenes were detected in TPB containing as little as 100 micrograms ml-1 sucrose monolaurate (SML) during the logarithmic growth phase compared to populations detected in TPB containing no SML. At 400 micrograms ml-1, SML was lethal to L. monocytogenes. Less marked inhibitory effects were observed with Staph. aureus. The addition of EDTA to broth containing SML had a synergistic effect on the inhibition of both organisms. The chelator alone had no effect at 100 micrograms ml-1 on either pathogen but was inhibitory at 200 micrograms ml-1. Inhibition of L. monocytogenes was more pronounced as the incubation temperature was decreased from 30 degrees C to 15 or 5 degrees C. The addition of 0.1% acetic or lactic acid to TPB minimized the inhibitory effect of 100 and 200 micrograms ml-1 SML during the first 32 h of incubation. Staphylococcus aureus behaved similarly, but not as dramatically, to L. monocytogenes when cultured in TSB supplemented with SML alone or SML and organic acids. A synergistic inhibitory effect of SML and EDTA on heat inactivation of L. monocytogenes was evident but the reverse phenomenon was observed with Staph. aureus. The effectiveness of SML in controlling the growth of L. monocytogenes and Staph. aureus in foods most likely to be contaminated with these pathogens should be further investigated.