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The composition characteristic of fatty acids and volatile organic compounds in Sargassum thunbergii, Enteromorpha prolifera, Gracilaria lemaneiformis, Bangia sp. and Porphyra yezoensis were studied in this paper, especially the metabolic pathway of 8-heptadecene, which was the characteristics volatile compounds in red algae Porphyra, to in-depth understanding of the metabolism composition and pathway, provide basic data for the further development and utilization of seaweed resources.The fatty acid composition in five kinds of economic algae, S. thunbergii, E. prolifera, G. lemaneiformis, Bangia sp. and P. yezoensis were studied in the present paper. The soluble components were extracted by the modified Bligh-Dyer method, separated and identified by gas chromatography-mass spectrometry (GC-MS), with C19:0 as internal control to determine the composition of lipid. The results showed that C14-C22 fatty acids were detectable from all of the five algae with total lipid contents varying between 12-19 mg/g. Unsaturated fatty acid was the main composition of fatty acid, which accounted for more than 60% while in turn polyunsaturated fatty acids (PUFAs), especially n-6 and n-3 PUFAs, were the main composition of unsaturated fatty acid. The content ratios of n-6/n-3 PUFAs were less than 2. The comparison of composition characteristics of fatty acid from these five algae results showed that fatty acid designated C16, C18 and C20 were the major composition in S. thunbergii, exhibiting typical fatty acid composition characteristic of brown algae. C16 and C18 were the major fatty acid composition in E. prolifera, the typical characteristic of green algae. Those of G. lemaneiformis, Bangia sp. and P. yezoensis contained mainly C16 and C20 which was also the typical characteristic of red algae. Meanwhile, differences between them, G. lemaneiformis was investigated and represented typical composition characteristic of Florideophycidae, while, Bangia sp. and P. yezoensis shown characteristic of Bangioideae.Applying headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS) in the analysis and identification of the volatile organic compounds in S. thunbergii, E. prolifera, G. lemaneiformis, Bangia sp. and P. yezoensis. The results showed that 32, 26, 27, 31, and 32 kinds of volatile organic compounds were identified; they were mainly hydrocarbons, alcohols, aldehydes and esters. Bangia sp. and P. yezoensis contained a small amount of alcohols, aldehydes and esters, mainly composed of hydrocarbons, which accounted for more than 60%, Particular 8-Heptadecene and heptadecane were the main content of more than half of the total composition, and more than 30% was 8-Heptadecene, which has small amount in Sargassum, Gracilaria and Enteromorpha. These results indicate that the volatile components composition have significant differences in algae species, It was similar in primitive red algae Bangia sp. and P. yezoensis, the 8-Heptadecene was the characteristic composition of Bangioideae.The metabolic pathway of 8-heptadecene in red algae was investigated. The results showed that the amounts of 8-heptadecene in the primitive red algae Porphyra and Bangia were 30-50% of the volatile compounds, much higher than that in the green alga Ulva pertusa, the brown alga S. thunbergii and the Florideophycidae alga G. lemaneiformis. Studies on the metabolism of 8-heptadecene in Porphyra found that its enzymatic system has no significant catalytic activity on palmitic acid, oleic acid, linoleic acid, linolenic acid and arachidonic acid. However, the isolated enzymatic system showed activity in the presence of eicosapentaenoic acid. This activity produced about four times the amount of 8-heptadecene compared with other substrates and the control, indicating the system had a specific catalytic function for eicosapentaenoic acid. Furthermore, the enzyme system was strongly inhibited by NaN3 but not by phenidone and phenanthroline, suggesting that the related enzyme is structurally related to heme protein. Thus, it is believed that a constant amount of 8-heptadecene is maintained in the primitive red alga Porphyra and that 8-heptadecene is a metabolite of eicosapentaenoic acid catalyzed by a heme lipoxygenase-like enzyme.
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