THE POLYUNSATURATED FATTY-ACID COMPOSITION OF BEEF AND LAMB LIVER

The effect on liver fatty acids of two typical beef production systems . steers fed grass (grazing) and bulls fed concentrates, was investiga ted. Liver fatty acids were also studied in lambs grazing grass. Total fatty acid content of liver in the beef animals was not affected by p roduction system, being 3.5% for grass and 3.7% for concentrates altho ugh carcasses of the latter animals were leaner. The percentages of th e major non polyunsaturated fatty acids (PUFA) were also similar. (con centrates in parentheses) 18:0, 25.2% (25.1%); 16:0, 13.3% (14.5%); 18 :1 12.6% (14.0%). Total liver PUFA contents were similar for the two p roduction systems and much higher than in muscle fr om the same animal s. All n-3 PUFA were present in greater amounts in liver from grass fe d animals and n-6 PUFA were higher in concentrate fed animals: mg/100 g liver, 18:3n-3 92 (32); 20:5 n-3, 151 (17); 22:5 n-3, 283 (108); 22: 6 n-3, 83 (32); 18:2 n-6, 172 (444); 20:4 n-6, 194 (270). The P:S rati os were 0.20 (grass) and 0.32 (concentrates) and the n-6:n-3 ratios we re 0.71 and 4.8, respectively. Livers from grass-fed lamb had a higher fat content, 4.9%, than the beef livers and a lower percentage of 18: 0, (21%); but more 16:0, (16%) and 18:1 (21%). Total PUFA content of l amb's liver resembled that of beef liver and the composition was simil ar to that of the steers fed grass. However the concentrations of 18:3 n-3 and 22:6 n-3 were higher in lamb and contributed to a lower n-6. n-3 ratio of 0.46 although the P:S ratio of 0 18 was similar to that i n beef liver. Ruminant liver is potentially a good source of C20 and C 22 PUFA in the human diet particularly from grass fed animals, with a highly desirable n-6:n-3 ratio and this may be more important nutritio nally than the low P:S ratio since people can offset this elsewhere in the diet. (C) 1998 Elsevier Science Ltd. All rights reserved.