# The Volatile Compounds Change during Fermentation of _Saccharina japonica_ Seedling
## 3 Results
### OAV Analysis of Volatile Compounds of S. japonica Seedling before and after Fermentation  
The odor activity value (OAV) is the ratio of the compound concentration to its flavor threshold [26]. An OAV \(\geq 1\) indicates that the compound is a significant contributor to the overall odor [27]. As shown in Table 2, the _S. japonica_ seedling before fermentation had 14 compounds with OAV \(\geq 1\), including 1-octen-3-ol, 2-octen-1-ol, 1-octanol, 1-nonanol, hexanal, 1-nonanal, 2-nonenal, 2,4-dimethylbenzaldehyde, decyl aldehyde, \(\beta\)-cyclocitral, trans-2,4-decadienal, dodecyl aldehyde, \(\beta\)-ionone, and 2-pentylfuran. Among these compounds, 1-octen-3-ol, 1-nonanal, and trans-2,4-decadienal, which had fishy odors, had the highest OAV values. Obviously, these three compounds are the main contributors to the fishy odor of the _S. japonica_ seedling. This result is consistent with the findings of [PERSON] et al. [16] and [PERSON] et al. [23]. After fermentation, the _S. japonica_ seedling had 7 compounds with OAV \(\geq 1\), including 1-nonanal, decyl aldehyde, \(\beta\)-cyclocitral, dodecyl aldehyde, and \(\beta\)-ionone. Among these volatiles, 1-nonanal exhibited earthy and fatty odors; decyl aldehyde had ocean, cucumber, and herbal stents; \(\beta\)-cyclocitral emitted liquorice, fruity, and fresh aromas; dodecyl aldehyde presented herbal, fatty, and soap odors; and \(\beta\)-ionone showed floral and raspberry odors. Moreover, after fermentation, the OAVs of 1-octen-3-ol, hexanal, and trans-2,4-decadienal decreased to 0, and the OAV of 1-nonanal decreased from 43,093 to 10,541. This indicates that the fishy malodor of the fermented _S. japonica_ seedling was dramatically reduced, while the floral and herbal notes were significantly enhanced. Combining Figure 1 with Figure 3A, the OAV results are consistent with sensory properties. Unfermented _S. japonica_ seedlings mainly present a fishy odor, which is reflected in OAV of trans-2,4-decadienal, 1-nonanal, and 1-octen-3-ol showing higher values. After fermentation, the sensory properties of the _S. japonica_ seedling exhibited stronger notes of green, floral, sweet, and fruity. The significantly higher levels of \(\beta\)-ionone, \(\beta\)-cyclocitral, and decyl aldehyde in the OAV support their role as contributors to green, floral, sweet, and fruity notes. Figure 2: Volatile compound concentrations in _S. japonica_ seedling before and after fermentation by _S. cerevisiae_. SJS means unfermented _S. japonica_ seedling. FSJS means fermented _S. japonica_ seedling. Comparing the OAV before and after fermentation, as shown in Figure 3B, it is evident that alcohols, aldehydes, and ketones make significant contributions to the overall aroma. Aldehydes exhibit the highest OAV, indicating that aldehydes are the main contributors to the odor of the _S. japonica_ seedling. After fermentation, the OAV of alcohols decreased to 0, while aldehydes decreased and ketones increased slightly. The change in the OAV of the _S. japonica_ seedling after fermentation indicates that aldehydes and ketones are the primary contributors to the fermented _S. japonica_ seedling odor. The OAV of alkanes, alkenes, and esters equals to 0, essentially indicating that these three compounds do not significantly contribute to the odor of the _S. japonica_ seedling.