1Fatty acid profi le of lamb semitendinous muscle and perirenal adipose tissue from two different genotypes*

The objective of this study was to determine the fatty acid composition of semitendinous muscle and perirenal adipose tissue of Sarda and crossbred Moufl on × Sarda lambs. Lambs were slaughtered at 40 days of age. Fatty acid composition was similar for S×S and crossbred SxM lambs. n-6/n-3 PUFA ratio was 2.30 in pure lambs and 2.90 in crossbred. In ST muscle of SxS lamb, index of atherogenicity was 0.95 and index of thrombogenicity was 1.01; in crossbred IA was 0.87 and IT was 1.01. Both genotypes were characterized by a FA profi le appropriate in relation to their contribution to health.


INTRODUCTION
Ovine meat production in Sardinia is based, nearly exclusively, on milk-fed lambs slaughtered at few weeks of age.This is due to different reasons such as economics and genetics.Indeed the commercial value of meat does not repay the milk used to product it and Sarda lambs tend to accumulate fat depots early.Moreover, traditionally in Italy, as in many countries of the Mediterranean Basin, lambs are slaughtered very young.Considering the growing demand for alternative meats, different strategies can be tried to improve meat quality.Among the quality parameters, lipids are important for their biological and organoleptic 682 properties (Berra and Rapelli, 1987).Moreover, some lipid fractions are believed to be linked with the incidence of coronary heart disease (CHD).Ulbricht and Southgate (1991) indicate some SFA (C12:0, C14:0 and C16:0) as atherogenic and some SFA as thrombogenic (C14:0, C16:0 and C18:0).Moreover, they indicate polyunsatured fatty acids (PUFA) of the n-6 (linoleic) and n-3 (linolenic) series, and monounsatured fatty acids (MUFA) as dietary factors protective against CHD.The same authors suggest an index of atherogenicity (IA) and thrombogenicity (IT) as a measure for nutritional evaluation of fat.Other authors consider more appropriate the poliunsatured/satured FA ratio (P/S) and n-6/n-3 PUFA ratio (Department of Health, 1994;Santos-Silva et al., 2002).In order to assess the fatty acid composition of semitendinous (ST) muscle and perirenal (PR) adipose tissue in milk-fed lambs, a trial was carried out on two different genotypes.

MATERIAL AND METHODS
In total twenty lambs were used in the trial, i.e. 10 Sarda (S×S) and 10 crossbred Moufl on (Ovis g. musimon) × Sarda (M×S).The animals suckled, without supplementation with solid feed, until slaughter at 40 days of age.The fatty acid composition of ST muscle and PR adipose tissue was determined after extraction of total lipids (Bligh and Dyer, 1959) and methylation with trimethylclorosilane (TMCS: Macherey-Nagel).Fatty acids methyl esters (FAME) were analysed on a Perkin Elmer Gas Chromatograph Mod.8500, equipped with a fl ame ionization detector (FID).Separations were performed using a Varian SP 2430 capillary column (50 m ×0.25 mm i.d.) and the following conditions: carrier gas, helium at 10 ml/min fl ow; injector temperature, 220°C; detector temperature 270°C; the temperature program employed was: 120°C for 5 min, 5°C/min for 20 min, 229°C for 5 min, 5°C/min for 5 min, 245°C for 3 min FAME standards Supelco and Matreya for determining retention times, Human Plasma Lipid FAME mix (Matreya) for response factors.The data obtained were submitted to Student t test, after angular conversion.

DISCUSSION
The data obtained were similar to those reported in literature (Bas and Morand-Fehr, 2000;Beriain et al., 2000).For both genotypes, the value obtained for n-6/n-3 PUFA ratio (2.15 S×S, 2.78 M×S), is below the recommendations of nutritional advisers, whose attempt is to increase the levels of n-3 PUFA in the diet, such that n-6/n-3 ratio does not exceed 4.0 (Department of Health, 1994).P/S (0.35 S×S and 0.41 M×S), is slightly below the recommended value for the diet, anyway such an index may not be an adequate way to assess the nutritional value of fat because it considers that all saturated FA induce an increase in cholesterol and ignore the effects of monounsatured FA (Santos-Silva et al., 2002).A better evaluation of the functional effects of FA on CHD may be given by the indices of atherogenicity (IA) and thrombogenicity (IT) (Ulbricht et al., 1991).In Sarda lamb ST muscle IA was 0.95, IT was 1.01; while in crossbred (M×S) IA was 0.87 and IT was 1.01.Likewise, C20:5 n-3 (EPA) and C22:6 n-3 (DHA) content in both genotypes is very higher than what has been reported for other lambs from different breeds (Sanudo et al., 2000).The importance of this datum is especially due to the evidence for biologic actions of long-chain omega-3 PUFA, such as anti-atherogenic and anti-thrombotic (Williams, 2000).

CONCLUSIONS
Fatty acid profi le of semitendinous muscle and perirenal adipose tissue is very similar in lambs of the two different genotypes that we considered for our investigation.ST muscle shows, compared to PR adipose tissue, a higher percentage of PUFA, as expected.Both atherogenicity and thrombogenicity indexes calculated, point out the good nutritional value of milk fed lambs' meats.In order to further increase the value of this important meat product we intend to investigate the levels of conjugated linoleic acid (CLA), which is very important for its potential health benefi ts, such as anti-carcinogenic properties.

Table 1 .
Mean percentage values (± d .s.) of the fatty acids analysed