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The TAG composition of 45 samples of ewe's milk, collected throughout the year from five Spanish breeds, was analyzed according to their carbon number by using short capillary column GC. The TAG content had a bimodal distribution with maxima at C 38 (12.8%) and C 52 (8.4%). The TAG composition did not vary significantly with respect to the time of year of sampling but was affected by the breed. Multiple regression equations based on TAG content are proposed to detect foreign fats in ewe's milk fat. Analysis of known mixtures of lard, palm oil, and cow's milk fat with ewe's milk fat have experimentally confirmed the accuracy of the equations.Paper no. J10404 in JAOCS 80, 219-222 (March 2003). KEY WORDS:Ewe's milk fat, foreign fat, short capillary column GC, triacylglycerols.The lipid fraction of milk and the products of its degradation, mainly volatile FFA, play an important role in the flavor of cheeses. Different studies have indicated that lipolysis depends on the composition of the TAG of ewe's milk fat, i.e., chain length and degree of unsaturation (1,2). Thus, Batelli and Peregrino (3) observed that lipolysis had a pronounced effect on TAG composition within a low M.W. range during prolonged ripening. The determination of TAG classes according to their carbon number (CN) has been reported as an effective criterion for assessing milk origin (4-6). TAG determination also has been proposed as a means to detect mixtures of foreign fats in milk fat and by the European Community (EC) as an official method for assessing cow milk fat purity (7). TAG composition has been studied in cow's and goat's milk but less so in ewe's milk, where most of the published data refer to a limited number of samples (2,(8)(9)(10)(11). The exception is a study carried out by Muir et al. (12) where samples were taken from ewes, mainly of the Frisone breed, for the duration of 1 yr.FA composition of milk fats varies considerably in response to factors such as feed. It has also been reported that the composition of TAG changes with lactation period (13) or season (12).The objective of this work was, first, to study the range of variation in the composition of TAG, using GC, in ewe's milk fat from five breeds located in different regions and collected throughout the year and, second, to propose multiple regression equations based on the TAG content to detect foreign fat in ewe's milk fat. MATERIAL AND METHODSSamples. Forty-five milk samples were collected at monthly intervals during the milking period from five ovine herds. They were taken from the storage tanks containing milk from the whole herd. Each herd consisted of a different breed: CH (Churra breed with 130 head), W (Awassi breed with 2,500 head), M (Manchega breed with 2200 head), A (Assaf breed with 480 head), A × C (cross between Assaf and Castellana breeds with 170 head). The herds were located in different parts of Spain. For statistical analysis, the samples were distributed in four groups or seasons.Samples from the herds M and W were taken through the year between January ...

-Identification and concentration of cholesterol and its precursors were investigated in ovine milk. In order to ensure a wide variety of milk composition, 45 samples were taken during the year from the bulk milk of five herds (ranging from 130 to 2500 adult ewes) corresponding to five breeds and located in different places in Spain. Gas chromatography/mass spectrometry analysis allowed the identification of small quantities of squalene, lathosterol, desmosterol, dihydrolanosterol and lanosterol. Neither campesterol nor b-sitosterol could be detected in the studied samples. The mean values (mg·100 g -1 fat) were: cholesterol 288.44 ± 42.22; squalene 1.80 ± 0.99; lathosterol 1.81 ± 0.82; desmosterol 0.41 ± 0.30; dihydrolanosterol 4.15 ± 2.40 and lanosterol 6.86 ± 1.88. With the statistical model used, the cholesterol concentration in milk fat was shown to be influenced by an interaction between the factors time of year of sampling and breed, but the variations observed do not show a clear trend.Cholesterol / minor sterols / ewe milk / fat / gas-chromatography / mass-spectrometry Résumé -Composition du cholestérol et de ses précurseurs dans le lait de brebis. L'identification du cholestérol et ses précurseurs a été effectuée sur le lait de brebis et leur concentration mesurée. Afin de garantir une large variété de composition du lait, 45 échantillons ont été prélevés tout au long de l'année sur une quantité de lait de cinq troupeaux (allant de 130 à 2500 agnelles adultes) correspondant à cinq races et localisées dans différentes régions d'Espagne. L'analyse par chromatographie gaz/spectrométrie de masse a permis d'identifier une petite quantité de squalène, lathosterol, desmosterol, dihydrolanosterol et lanosterol. Ni le campesterol ni le b-sitosterol ne pouvaient être détectés dans les échantillons étudiés. Les valeurs moyennes (mg·100 g -1 de matière grasse) ont été : cholestérol 288,44 ± 42,22; squalène 1,80 ± 0,99; lathosterol 1,81 ± 0,82; desmosterol 0,41 ± 0,30; dihydrolanosterol 4,15 ± 2,40 et lanosterol 6,86 ± 1,88. Les modèles statistiques utilisés ont permis l'observation d'une interaction entre l'effet période de l'année pour l'échantillonnage et la race sur la concentration du cholestérol dans la matière grasse du lait, mais les variations observées ne furent pas claires.Cholestérol / stérol mineur / lait de brebis / matière grasse / chromatographie gaz / spectrométrie de masse

-Ewe's milk fat obtained from the milk of five different herds were studied to characterize main and minor fatty acids using a combination of gas chromatography and mass spectrometry. In order to assess monounsatured trans fatty acids content, fatty acid methyl esters (FAME) were fractionated by silver ion thin-layer chromatography prior to gas chromatography analysis. Trans fatty acids (TFA), including conjugated linoleic acid, represented 4.9% of the total FAME; most of them belonged to C18:1 trans isomers (2.9%) with a small range of variation (2.5-3.2%). The distribution profile of trans-C18:1 molecules indicated that more than half were trans-11, whereas the proportion of potentially unhealthy compounds (trans-10 and trans-9 C18:1) was less than 10%. Mean trans-C16:1 content was 0.25% of total FAME. The sum of the different trans-C18:2 isomers (excluding conjugated linoleic acid) was 0.88% and C18:3 trans isomers represented 0.16%. Ewe's milk / fatty acid / trans fatty acidRésumé -Caractérisation quantitative des acides gras insaturés et trans de la matière grasse du lait de brebis. Les acides gras mineurs et majeurs du lait de brebis provenant de cinq troupeaux différents ont été caractérisés par chromatographie gazeuse associée à la spectrométrie de masse. En vue de connaître le contenu en acides gras monoinsaturés trans, les esters méthyliques des acides gras ont été fractionnés en recourant à la chromatographie sur couche mince à l'ion argent suivie d'une analyse par chromatographie gazeuse. Les acides gras trans, incluant l'acide linoléique conjugué, représentaient 4,9 % du total des esters méthyliques des acides gras. La plupart d'entre eux appartenaient aux isomères trans du C18:1 (2,9 %) avec une variation faible entre les échantillons (2,5-3,2 %). Le profil de distribution des molécules C18:1 trans montraient que plus de la moitié étaient des trans-11, tandis que les proportions de trans-10 et trans-9, potentiellement nuisibles à la santé, étaient inférieures à 10 %. La teneur moyenne en C16 :1 trans était de l'ordre de 0,25 % du total des esters méthyliques des acides gras. Le total des différents isomères C18:2 trans (à l'exception de l'acide linoléique conjugué) et C18:3 représentait respectivement 0,88 % et 0,16 % du total.