*4.1.2 Amine compounds*

*Essential Oils - Bioactive Compounds, New Perspectives and Applications*

(*E. intestinalis* and *A. centralis*) [51].

**4.1 Common volatile organic compounds of macroalgae**

The alkanes and alkenes are common compounds in the majority of volatile fraction and essential oils of marine macroalgae. The chemical composition reveals the presence of the linear and branched saturated hydrocarbons from C7 to C36 [37, 52–54], the unsaturated hydrocarbons from C8 to C19 with the presence of 1 [37, 52–54] to 4 degrees of unsaturation [55] in the volatile fraction obtained by several extraction techniques. We also noted the presence of mono- and di-alcohol of C4–C18 [37, 52–54, 56, 57]. Some short-chain (C6, C9) and middle-chain (C10) aliphatic aldehydes are formed in marine algae from fatty acids (C20), whereas they are formed from C18 in higher plants [58–60]. Also, it has been reported that long-chain aldehydes (C14, C17) of the green alga *U. pertusa* [61, 62] are formed by decomposition of fatty acids through the corresponding 2-hydroperoxy acid; this later are encountered in a variety of marine algae [63, 64]. In addition to aldehydes, the ketone compounds were commonly reported in the aroma composition of algae [65]; the presence of β-ionone and 6-methyl-5 hepten-2-one which are formed via the oxidative cleavage of carotenoids such as lycopene and phyotene was mentioned [66]. β-ionone, present in several essential earth oils, is a powerful odorant for the perfume industry. 6-methyl-5-hepten-2-one, in addition to its pleasant fragrant note, is often used as an intermediary in the synthesis of several monoterpenes highly valorized in perfumery. In addition, other simple ketone (C6▬C19) compounds such as maltol [53], octan-3-one [57], nonacosan-2-one [67], and undeca-1,4-dien-3-one [42] are identified in the volatile fractions of algae. Saturated fatty acids from C3 to C18 and their ester derivatives have also been identified in the chemical composition of volatile algae fractions [37]. Unsaturated fatty acids and their corresponding esters, in particular Eicosa-5,8,11,14-methyltetraenoate and Eicosa-5,8,11,14,17-methyl-pentaenoate [42], are usually found; this is probably related to their implications in biosynthetic processes

*4.1.1 Hydrocarbons and oxygenated hydrocarbons*

researches in 1951–1961 [32] and Moore prior to 1966 [33]. The volatile organic compounds in marine algae, as in plants and fungi, released into the seawater, are involved in the chemical communications process; these compounds play an important role as either pheromones or allelochemicals for communication and interaction with the surrounding environment [34, 35]. The species produce the volatile organic compounds in closed relation to their physiology; the algae must adapt to abiotic stresses of their ecosystem [36]. The volatile components of marine algae contain a mixture of chemical classes such as terpenes, hydrocarbons, fatty acids, esters, alcohols, aldehydes, ketones [37–41], C11-hydrocarbons [33, 42], polyphenols and derivatives [43, 44], and halogenated [45] and sulfur compounds [46, 47]. The distinctive ocean smell is due to the presence of terpenes, but particularly, to a fraction of acyclic and cyclic non-isoprenoid C11-hydrocarbons acting as pheromones and playing an important role in the chemical communication [48], it seems to be most abundant in brown algae of the genus *Dictyopteris* [33]. As for terrestrial plants, the monoterpenes identified in algae such as linalool, citral, geraniol, and terpinolene, 1,8-cineole, α-pinene and β-pinene, and eugenol and isoeugenol could be valued in perfumery. While the disagreeable odor is related to amines and halogenated, sulfurous, and other specific compounds [49], the dimethyl sulfide, mainly distributed in Chlorophyta and in some Rhodophyta [50], has a very unpleasant odor molecule. It results from the enzymatic cleavage of dimethyl-2-carboxyethylsulfonium hydroxide, from the green algae species

**6**

of other metabolites.

The amine compounds have been described several times in marine algae [68–70]; the small amine molecules such as methyl amine, dimethylamine, ethylamine, and propylamine were found in algae [71]. The volatile amines in algae result from decarboxylation of amino acids [71]. Although present in brown and green algae, the amine compounds were especially found in red algae.
