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 mug/ml. The media were inoculated with similar to10(3) cfu/ml of L. monocytogenes strain Scott A and incubated at 32degreesC 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 5degreesC for 21 days showed log cfu/g of: 8.5 (control), 7.3 (500 mug/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 mug/g, monolaurin and lauric acid caused similar delayed growth effects at 5degreesC, 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. (C) 2004 Elsevier Ltd. All rights reserved.