Notable differences of FA profile were observed among tissues or groups of tissues (Table 3.6, 3.7). The FA profile of liver differed from that of the other tissues for the large majority of the single SFA, MUFA PUFA. In addition, 5 long chain FA were found only in liver samples, among which the C22:6n3 (DHA) and other 3 long chain FA were detected only in liver and kidney fat (Table 3.8).
Compared to the other tissues, liver contained smaller proportions of SFA and MUFA and a much greater proportion of PUFA (Table 3.9). In addition, the proportion of unknown FA
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was greater in liver compared to the average of the other tissues. Liver tended to contain a slightly greater proportion of ΣCLA (P = 0.06), but also contained a greater proportion of ω3 and ω6 FA, being the ω3 and the ω6 contents 6 to 7-fold and 3 to 4-fold greater than the average of the other tissues, respectively. The ω6/ω3 ratio in liver was about 50% smaller than the average value found for the other tissues. Liver also evidenced a smaller proportion of short- and medium-chain FA, and a greater proportion of long- and odd-chain FA compared to the other tissues. The overall Δ9-desaturation index was lower in liver than in other tissues (Table 3.9), mainly because the incidence of smaller values found for the C18 index. On the opposite, the CLAc9,t11 desaturation index was greater in liver compared to the other tissues. Both the thrombogenicand atherogenic indices values computed for liver were about 50% smaller (more favorable) than the values computed for the other tissues.
The FA profile of the two fatty tissues was different from that of muscles, with exceptions for some FA (Table 3.6). In the case of saturated FA the differences between fat and muscle tissues in the FA proportions regarded the large majority of individual FA, in particular of the minor FA (those representing less than 1% of total FA). In the case of unsaturated FA, differences in the FA proportions between fats and muscles were found also for all the major FA (Table 3.7).
In terms of FA categories (Table 3.9), fatty depots had greater SFA and smaller MUFA and PUFA proportions, greater proportions of unknown FA and ω3 FA, smaller proportion of ω6 FA, lower ω6/ω3 ratio, similar short- medium- and long-chain FA proportions, and greater proportions of branched and odds chain FA compared to muscles. The total desaturation index of fatty tissues was lower and the thrombogenic and atherogenic indices were greater compared with that of muscles.
The FA profile of kidney fat frequently differed from that of cover fat, particularly for the greater proportion of SFA (Table 3.9), almost exclusively due to a greater incidence of C18:0 (Table 3.6), and a smaller proportion of MUFA, mainly due to a smaller proportion of C18:1c9 (Table 3.7). In addition, in kidney fat 7 very long-chain unsaturated FA that were not detected in the subcutaneous cover fat were found (Table 3.8). Kidney fat compared to subcutaneous cover fat was characterized by the presence of unknown FA in trace, a greater proportion of ΣCLA, a smaller proportion of ω6 FA, and a lower ω6/ω3 ratio. Kidney, had greater proportion of short- and long-chain FA, a smaller proportion of medium-chain FA, and a greater incidence of odd-chain FA, compared to cover fat. In kidney fat the values of the desaturase indices were smaller, particularly for C16 and C18, and the thrombogenic and atherogenic indices were greater compared to cover fat (Table 3.9).
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Also within the 3 muscles several differences were found in all classes of FA, but in this case, even if statistically significant, the magnitude of the differences among muscles was smaller compared to that found in the previous comparisons (Tables 3.6, 3.7 and 3.9). The general trend was that the other chop muscles tended sometimes to have a FA profile intermediate between that of the leg and rib-eye muscles and that of the fatty depots.
Lastly, the large majority of individual FA and of their groups and indices showed interactions regarding the effects of feeding system in different tissues. The number of traits that evidenced a significant interaction (41 among FA, groups and indices) and the complexity of the interaction (18 least square means with 10 df for each one) make impossible to detail all these interactions, but some examples of interest for human health are presented and discussed. Pasture and rpCLA supply increased the proportion of the CLAt10,c12 isomer in all tissues compared to the system based on hay and concentrate, and the magnitude of response to rpCLA supply was similar to that achieved with pasture, except for kidney fat where a notable increase of this isomer was found when rpCLA was offered to the lambs (Figure 1). Among tissues, liver evidenced the highest proportions of both ω3 and ω6 FA, and in all tissues pasture increased the proportion of ω3, decreased the proportion of ω6 and decreased the ω6/ω3 ratio compared to the other feeding systems (Figure 2). The ω6/ω3 ratio was lowest with pasture in all tissues. Irrespective of the feeding treatment this ratio ranged 1.0 to 2.5 and 2.5 to 6.0 in liver and other tissues, respectively. With pasture the proportions of branched and odd FA were lower compared to those found for the other feeding systems in almost all tissues, but pasture decreased the proportion of these FA more in liver and kidney than in other tissues (Figure 3).
3.5 DISCUSSION
The GC×GC technique offers high separation efficiency and enhanced sensitivity compared to single column GC (Adahchour et al., 2008). A further characteristic of the GC×GC technique is the ordered structure of the chromatograms (Vlaeminck et al., 2007; Adahchour et al., 2008), which makes the identification of compounds more reliable than in traditional GC, particularly when columns with different polarity are used (Manzano et al., 2011). The GC×GC is also well suited for the analysis of samples where compounds are present in very different concentrations. Compared with other biological samples, beef meat fat is a complex matrix. To our knowledge this is one of the first time that such technique has been applied to analyse the FA profile of lamb’s meat. The potential of this technique is highlighted by the
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106 different FA detected. This would open new perspectives to improve the knowledge of lipid metabolism in ruminants.