# Seasonal Monitoring of Volatiles and Antioxidant Activity of Brown Alga _Cladosteplus spongiosus_
## 2 Results and Discussion
### Headspace Volatilome Variations of C. spongiosus  
Two fibres of different polarity, divinylbenzene/carboxylate/polydimethylsiloxane (DVB/CAR/PDMS, f1) with medium polarity and polydimethylsiloxane/divinylbenzene (PDMS/DVB, f2) with high polarity, were used to study the headspace composition. Aliphatic compounds accounted for the majority of compounds identified in all samples from four consecutive months. Their lowest percentage was in the air-dried sample in May (36.90%, f1; 35.93%, f2) and the highest in the air-dried sample in August (91.14%,f1; 89.30%, _f2_). When extracted with f1 (fibre of medium polarity), hydrocarbons were dominant in both the fresh and dry samples from June (23.02%; 47.01%) and from August (26.28%; 65.94%) and in the dry sample from July (47.01%) (Figure 1). Extraction with the more polar f2 fibre resulted in a dominance of hydrocarbons only in the dry samples from June (35.70%), July (35.96%), and August (65.16%) (Figure 2). In the dry samples, hydrocarbons were more than twice as high as in the fresh samples, except in May, when they were more abundant in the fresh samples. Pentadecane dominated with the highest abundance in August samples (43.88%, f1; 35.68%, f2) (Tables 1 and 2). This result is consistent with previous findings on the predominance of pentadecane in brown algae [16]. Other abundant hydrocarbons were pentadec-1-ene and heptadecane. Hydrocarbons are likely formed as oxidative degradation products of lipids [17]. Figure 1: The volatile organic compounds (VOCs) from _Cladosteplus spongiosus_ sorted by structural groups obtained by headspace solid-phase microextraction (HS-SPME) with divinylbenzene/carboxene/polydimethylsiloxane fibre (f1) and analysed by gas chromatography–mass spectrometry (GC-MS): (**a**) fresh (Fr) samples; (**b**) dry (Dr) samples. Aliphatic alcohols were present with high percentages in all months studied, especially when extracted with the fibre f2 (Figure 2), and they were more abundant in the fresh samples. The short-chain alcohols ethanol, hexan-1-ol, octan-1-ol, and oct-1-en-3-ol were the most abundant (Tables 1 and 2). Previous studies showed that the oxylipin oct-1-en-3-ol is a defence compound in marine algae [18; 19; 20]. Hexanal, heptanal, nonanal, and tridecan constituted the majority of aldehydes (Tables 1 and 2). The algal aldehydes are formed through degradation of fatty acids, which can occur either via oxidation or via the enzymatic action of lipoxygenases [21]. Hexanal and heptanal are mainly derived from linoleic acid [22; 23]. Nonanal could originate from \(\omega\)9 monounsaturated fatty acids (MUFAs) and \(\omega\)6 polyunsaturated fatty acids (PUFAs), such as linoleic acid [24]. The fatty aldehyde tridecanal could be derived from long-chain fatty acids. Aldehydes obtained with the polar fibre f2 were more abundant in the air-dried samples in all months. Figure 2: The volatile organic compounds (VOCs) of _Cladostelmus spongiosus_ sorted by structural groups obtained via headspace solid-phase microextraction (HS-SPME) with polydimethylsiloxane/divinylbenzene fibre (f2) and analysed via gas chromatography–mass spectrometry (GC-MS): (a) fresh (Fr) samples; (b) dry (Dr) samples. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \multirow{2}{*}{**No.