Antilisterial effects of free fatty acids and monolaurin in beef emulsions and hot dogs

This study was undertaken to screen fatty acids, conjugated isomers of linoleic acid (CLA), and monolaurin for antilisterial effects in broth, and to further test the active compounds in cooked comminuted beef and hot dogs. Capric, lauric, myristic, palmitic, stearic, oleic, linoleic, and linolenic acid, CLA and monolaurin were screened in sterile nutrient broth at concentrations of 5 to 700 μg/ml. The media were inoculated with 10³ cfu/ml of L. monocytogenes strain Scott A and incubated at 32°C for up to 8 days. Cell enumeration data showed that lauric acid was most inhibitory, followed by monolaurin, and capric acid. Tests in comminuted sterile beef stored at 5°C for 21 days showed log cfu/g of: 8.5 (control), 7.3 (500 μg/g lauric acid), and 4.7 (500 lauric acid+300 capric acid). Similar results were observed in beef hot dog emulsion to which lauricidin, lauric acid, capric acid, and the acid combination were added prior to heat treatment. At 500 μg/g, monolaurin and lauric acid caused similar delayed growth effects at 5°C, whereas the combination of the two acids showed enhanced inhibition on prolonged storage. Nonetheless, the observed 5-log increase in numbers of L. monocytogenes during 45 days of storage indicates limited control of the pathogen in refrigerated cooked meat products.