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We developed a new method for monitoring the distribution of administrated fatty acids in the body by combination of a stable isotope-labeling technique and imaging mass spectrometry (IMS). The developed stable isotope-labeling technique is very simple and able to adapt to all the fatty acid species. In this study, we synthesized stable isotope-labeled arachidonic acid (AA) and docosahexaenoic acid (DHA), and they were simultaneously administrated to mice to examine their migrations and distributions in the brain. The administrated AA and DHA have two more molecular weights compared to the originals and apparently were distinguished from the originally accumulated AA and DHA in the brain using IMS. As a result, we reveal that the administered AA and DHA first accumulated in the hippocampus and cerebellar cortex in the brain. This technique does not use radio isotopes and would appear to elucidate the role of all kinds of fatty acid species in the body.

IntroductionButter flavor can be attributed to a mixture of many volatile compounds. More than 230 volatile compounds have been identified as natural constituents of milk fat 1 . Among them, lactones are important compounds that impart flavor to butter and other dairy products. Therefore, these are used as flavor additives for the production of margarines to enhance their butter flavor. To date, many researchers have studied the lactone composition of milk fat. For instance, δ-decalactone as a coconut-like flavor of milk fat was identified by Keeny et al. 2 , and δ-decalactone and δ-dodecalactone were detected from the steam distillate of butter by Tharp et al. 3 . Boldingh et al. detected δ -o c t a l a c t o n e , δ -d e c a l a c t o n e , δ -d o d e c a l a c t o n e , δ-tetradecalactone, and smaller amounts of γ-lactones in milk fat as desirable contributors to the flavor of butter 4 .Siek et al. compared the aroma thresholds of the individual lactones, and reported the thresholds for δ-octalactone, δ-decalactone, δ-dodecalactone, and δ-tetradecalactone as 3.0, 1.4, 95.0, and 500 ppm in oil, respectively; the thresholds in water were 5 to 950 times lower than those in oil 5 . Although short chain lactones indicate lower thresholds Abstract: The lactone content of butter, fermented butter, and margarine was compared using gas chromatography-mass spectrometry. The main lactones in butters and fermented butters consisted of δdecalactone, δ-dodecalactone, δ-tetradecalactone, δ-hexadecalactone, and γ-dodecalactone. In contrast, the main lactones in margarines were δ-decalactone and δ-dodecalactone. The total lactone content in butters and fermented butters increased by approximately two-fold upon heat treatment, whereas, heat treatment did not affect the lactone content in margarine. The changes in lactone content caused by heat treatment were greater in fermented butters than in butters. These findings suggested that the fermentation process could increase lactone or lactone precursor content in butter.

INTRODUCTION Metabolic syndrome is associated with an increased risk of developing diabetes and cardiovascular disease. It is also associated with the accumulation of triglyceride TG in the liver and increased levels of cholesterol Ch and TG in the blood. Both genetic and dietary factors are known to play a role in the onset of the syndrome 1 3. For example, the Japanese have a much lower rate of cardiovascular disease compared to the Europeans and Americans 4. One of the reasons for this is thought to be the fact that fish has played a central role in the Japanese diet for a long time 5. Fish oil possesses attributes that can suppress the development of cardiovascular diseases and could play a role in the

Fatty acids in triacylglycerol (TAG) are catabolized after digestion. However, the catabolic rates of several fatty acids bound to the α (sn-1, 3) or β (sn-2) position of TAG have not been thoroughly compared. In this study, the catabolic rates of 13 C-labeled palmitic acid, oleic acid, linoleic acid, α-linolenic acid, eicosapentaenoic acid (EPA), or docosahexaenoic acid (DHA) bound to the α and β position of TAG were compared using isotope ratio mass spectrometry. The catabolic rates of the studied fatty acids were evaluated using the ratio of 13 C and 12 C in carbon dioxide expired from mice. The results indicated that palmitic acid, oleic acid, or α-linolenic acid bound to the β position was slowly catabolized for a long duration compared to that when bound to the α position. In contrast, EPA bound to the β position was quickly catabolized, and EPA bound to the α position was slowly catabolized for a long time. For linoleic acid or DHA, no difference in the catabolic rates was detected between the binding positions in TAG. Furthermore, EPA and DHA were less catabolized than the other fatty acids. These results indicate that the catabolic rates of fatty acids are influenced by their binding positions in TAG and that this influence on the catabolic rate differed depending on the fatty acid species.