Abstract
Fatty acid (FA) signatures (FAS) are important tools to assess the foraging ecology of wild animals. The present study was conducted to assess how well the general FAS and the proportions of individual FA are preserved in fat samples stored at different temperatures (–196, –80, –20, +4 and +20°C). Using three species (laboratory rat, American mink and rainbow trout), FAS were determined immediately upon sampling. Thereafter, eight subsamples per storage temperature from the inner part of the sample unaffected by oxygen and light were re-analyzed after 1, 2, 3, 7, 28, 84 and 168 days. Each time the remaining sample was sealed in its vial after replacing air with nitrogen gas. The results were tested with the mixed model and discriminant analyses. Generally, the FAS were well preserved regardless of storage temperature, and only a few major FA showed significant changes even after the 6-month period at room temperature. After an initial first-day change in proportions, presumably due to post-mortem enzymatic activities, the remaining minor changes could not be clearly attributed to either further autolysis, decomposition or autoxidation. In the discriminant analysis, the species-specific differences dominated and remained distinct even after 6 months. Furthermore, the analysis mostly classified the samples preserved at sub- and above-freezing temperatures separate from each other, and the general deviation from the initial analysis results was present as early as after 1 day. If FAS are to be analyzed in a very precise manner, the analysis should be performed immediately upon sampling. However, FAS remain adequately reliable for long periods of time even without preservation in deep freeze, widening the availability of potential samples for studies on foraging ecology and related disciplines.
Highlights
Fatty acid (FA) signatures (FAS; relative proportions of individual FA) yield information about the long-term nutrition of animals and humans and have practical applications, for instance, in foraging ecology, where they can be used to examine spatial and temporal differences in diets within and between species [1,2,3,4]
Proportions of major FA remained stable while small increases were detected for minor polyunsaturated FA (PUFA), which did not jeopardize the analysis of samples preserved for up to 10 years
The results of the present study clearly showed, how the fatty acid signature (FAS) remained unexpectedly stable for 6 months despite the very different storage Ta
Summary
Fatty acid (FA) signatures (FAS; relative proportions of individual FA) yield information about the long-term nutrition of animals and humans and have practical applications, for instance, in foraging ecology, where they can be used to examine spatial and temporal differences in diets within and between species [1,2,3,4]. FAS can remain relatively stable even for long periods of time when biological samples are stored frozen. Proportions of major FA remained stable while small increases were detected for minor polyunsaturated FA (PUFA), which did not jeopardize the analysis of samples preserved for up to 10 years. Human blood samples showed only a few small changes in the plasma triacylglycerol (TAG) and erythrocyte phosphatidylcholine fractions after 2–2.5 years of storage at –80 ̊C [6]. Both the above studies suffer from the fact that there were no initial FA analyses upon sampling but the samples were analyzed for the first time only after 0.5–1.5 years. The FA composition of biopsies from human subcutaneous fat remained stable at – 80–+4 ̊C for 1.5 years [7]
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