The response of Campylobacter jejuni to low temperature differs from that of Escherichia coli.

Human infection with Campylobacter jejuni is often associated with the consumption of foods that have been exposed to both chilling and high temperatures. Despite the public health importance of this pathogen, little is known about the effects of cold exposure on its ability to survive a subsequent heat challenge. This work examined the effect of rapid exposure to chilling, as would occur in poultry processing, on the heat resistance at 56 degrees C of two C. jejuni strains, 11168 and 2097e48, and of Escherichia coli K-12. Unlike E. coli K-12, whose cold-exposed cells showed increased sensitivity to 56 degrees C, such exposure had only a marginal effect on subsequent heat resistance in C. jejuni. This may be explained by the finding that during rapid chilling, unlike E. coli cells, C. jejuni cells are unable to alter their fatty acid composition and do not adapt to cold exposure. However, their unaltered fatty acid composition is more suited to survival when cells are exposed to high temperatures. This hypothesis is supported by the fact that in C. jejuni, the ratio of unsaturated to saturated fatty acids was not significantly different after cold exposure, but it was in E. coli. The low-temperature response of C. jejuni is very different from that of other food-borne pathogens, and this may contribute to its tolerance to further heat stresses.

Effects of including a ruminally protected lipid supplement in the diet on the fatty acid composition of beef muscle.

Enhancing the polyunsaturated fatty acid (PUFA) and decreasing the saturated fatty acid content of beef is an important target in terms of improving the nutritional value of this food for the consumer. The present study examined the effects of feeding a ruminally protected lipid supplement (PLS) rich in PUFA on the fatty acid composition of longissimus thoracis muscle and associated subcutaneous adipose tissue. Animals were fed ad libitum on grass silage plus one of three concentrate treatments in which the lipid source was either Megalac (rich in palmitic acid; 16 : 0) or PLS (soybean, linseed and sunflower-seed oils resulting in an 18 : 2n-6:18 : 3n-3 value of 2.4:1). Treatment 1 contained 100 g Megalac/kg (Mega, control); treatment 2 (PLS1) contained 54 g Megalac/kg with 500 g PLS/d fed separately; treatment 3 (PLS2) contained no Megalac and 1000 g PLS/d fed separately. The PLS was considered as part of the overall concentrate allocation per d in maintaining an overall forage:concentrate value of 60:40 on a DM basis. Total dietary fat was formulated to be 0.07 of DM of which 0.04 was the test oil. Total intramuscular fatty acids (mg/100 g muscle) were decreased by 0.31 when feeding PLS2 compared with Mega (P<0.05). In neutral lipid, the PLS increased the proportion of 18 : 2n-6 and 18 : 3n-3 by 2.7 and 4.1 on diets PLS1 and PLS2 v. Mega, respectively. Similar responses were noted for these fatty acids in phospholipid. The amounts or proportions of 20 : 4n-6, 20 : 5n-3 or 22 : 6n-3 were not influenced by diet whereas the amounts and proportions of 22 : 4n-6 and 22 : 5n-3 in phospholipid were decreased with inclusion of the PLS. The amounts of the saturated fatty acids, 14 : 0, 16 : 0 and 18 : 0, in neutral lipid were on average 0.37 lower on treatment PLS2 compared with Mega. Feeding the PLS also decreased the proportion of 16 : 0 in neutral lipid. The amount of 18 : 1n-9 (P=0.1) and the amount and proportion of 18 : 1 trans (P<0.01) were lower on treatments PLS1 and PLS2 in neutral lipid and phospholipid. Conjugated linoleic acid (cis-9, trans-11) was not influenced by diet in the major storage fraction for this fatty acid, neutral lipid. The PUFA:saturated fatty acids value was increased markedly (x2.5) with inclusion of the PLS (P<0.001) while the Sigman-6 : n-3 value increased slightly (x1.2; P=0.015). The results suggest that the protected lipid used, which was rich in PUFA, had a high degree of protection from the hydrogenating action of rumen micro-organisms. The PLS resulted in meat with a lower content of total fat, decreased saturated fatty acids and much higher 18 : 2n-6 and 18 : 3n-3. The net result was a large shift in polyunsaturated: saturated fatty acids, 0.28 v. 0.08, on feeding PLS2 compared with Mega, respectively.