Antagonistic effect of fat on the antibotulinal activity of food preservatives and fatty acids

The effect of fat on the antibotulinal activity of 11 food preservatives, 12 free fatty acids, and nine lots of enzyme-modified cheese (EMC) was evaluated in a media system. Anhydrous milkfat or soybean oil was added to tubes of Trypticase-peptone-glucose-yeast extract medium (TPGY) supplemented with the additives (final pH adjusted to 5.9). Treatments were inoculated with 3-log(10) proteolytic Clostridium botulinum spores/ml (10-strain mixture of serotypes A and B) and incubated anaerobically at 30degreesC for up to 14 days. For the preservative and fatty acids studies, growth of C botulinum was determined by measuring optical changes at OD640 nm. Botulinal toxin production was determined in EMC-treatments using the mouse bioassay. Data revealed that the antibotulinal effects of nisin, and free fatty acids caprylic, capric, lauric, myristic, oleic, and linoleic acids were each significantly reduced in treatments supplemented with 20% fat (P < 0.05). Similar trends were observed in TPGY supplemented with 20% fat and potassium sorbate, sorbic acid, monolaurin, polyphosphate emulsifier, or EDTA-lysozyme, but the differences were reduced. Fat was also antagonistic to the antibotulinal activity of five EMC-treatments. This study suggests that fat may reduce the efficacy of some antimicrobials added to or found naturally in foods. (C) 2004 Elsevier Ltd. All rights reserved.