# The Volatile Compounds Change during Fermentation of _Saccharina japonica_ Seedling
## 4 Discussion  
It is important to eliminate the fishy odor in seafood, as this is a practical approach to enhance the flavor quality of seafood and encourage consumption [21; 28; 29; 30]. The _S. japonica_ seedling, which is the _S. japonica_ harvested at the early growth stage and considered a new food material, was first investigated in terms of its aroma profile, aroma-active volatiles, and aroma enhancement through fermentation. One of the objectives of this study was to identify the volatile compounds that contribute to the off-flavor of the _S. japonica_ seedling. The result of this study, showing that the _S. japonica_ seedling has 43 volatile compounds, is consistent with the findings of [PERSON] et al. [17]. Among these volatile compounds, 1-nonanal and hexanal were the most abundant in concentration. Furthermore, 1-nonanal, hexanal, and 1-octen-3-ol were the main contributors to the fishy odor of the _S. japonica_ seedling. [PERSON] et al. [16] reported that 1-octen-3-ol is a typical volatile compound contributing to the fishy odor in kelp. [PERSON] et al. [31] reported that hexanal and nonanal play an important role in determining the fishy odor of seaweed samples. Thus, this study identifies the presence of 1-octen-3-ol, trans-2,4-decadien, 1-octen-3-one, and hexanal as responsible for the pronounced fishy odor in the _S. japonica_ seedling, which is identical to the fishy odor reported in previous studies by [PERSON] et al. [16] and [PERSON] et al. [31]. This is the first study on the volatile compounds of the _S. japonica_ seedling that adds to our understanding of aroma volatile compounds in seafood. The second aim of the study was to investigate the effectiveness of fermentation with _S. cerevisiae_ in enhancing the aroma of the _S. japonica_ seedling. Several groups of volatile compounds increased after fermentation, including \(\beta\)-ionone (108.4 \(\mathrm{\SIUnitSymbolMicro g}\)/g), \(\beta\)-cyclocitral (20.5 \(\mathrm{\SIUnitSymbolMicro g}\)/g), D-limonene (8.3 \(\mathrm{\SIUnitSymbolMicro g}\)/g), dodecyl aldehyde (4.1 \(\mathrm{\SIUnitSymbolMicro g}\)/g), and decyl aldehyde (7.1 \(\mathrm{\SIUnitSymbolMicro g}\)/g). OAV results indicated that these volatile compounds contributed floral and fruity notes. The sensory characteristics of the fermented _S. japonica_ seedling showed enhanced notes of green, floral, sweet, and fruity aromas. Thus, this study identifies \(\beta\)-ionone, \(\beta\)-cyclocitral, DL-limonene, dodecyl aldehyde, and decyl aldehyde as the key fragrance components in the _S. japonica_ seedling. [PERSON] et al. [32] reported that _Gracilaria lemaneiformis_ produced floral and fruity aroma compounds after fermentation, with \(\beta\)-cyclocitral being the main aroma contributor. [PERSON] et al. [23] reported that D-limonene is the main sweet contributor of _Bangia fusco-purpurnea_. \(\beta\)-Ionone, \(\beta\)-cyclocitral, D-limonene, dodecyl aldehyde, and decyl aldehyde belong to terpenoids. The increase in terpenoids after fermentation may be due to the mevalonic acid (MVA) pathway in _S. cerevisiae_. The MVA pathway involves a series of enzymatic reactions starting with acetyl-coenzyme A (acetyl-CoA) and culminating in the production of isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) [33; 34]. Enzymes pivotal to this pathway include mevalonate kinase, phosphomevalonate kinase, and mevalonic acid dehydrogenase [35]. IPP and DMAPP are the basis for the synthesis of all terpenoid compounds [36]. The results showed that fishy odor contributors such as 1-octen-3-ol, trans-2,4-decadienal, 1-octen-3-one, and hexanal completely disappeared after fermentation with _S. cerevisiae_. Additionally, the concentration of 1-nonanal decreased from 47.4 \(\pm\) 1.7 to 11.6 \(\pm\) 1.5 \(\mathrm{\SIUnitSymbolMicro g}\)/g. The results indicated that the fishy odor of the _S. japonica_ seedling was dramatically weakened after fermentation with _S. cerevisiae_. This finding is consistent with the studies of [PERSON] et al. [23] and [PERSON] et al.