## 3 Results and Discussion
### Monitoring the Volatile Compound Profiles in Seaweed Fermentation
#### 3.3.2 Laminaria sp.  
The PCA of chemical groups of volatile compounds in the unfermented and fermented _Laminaria_ sp. is shown in Figure 5. The results showed that these variables could explain 91.7% of the total variances among the samples. BS and SC are located in the positive axis of PC1, whereas the unfermented group is in the negative axis of PC1 (Figure 5A). Therefore, fermenting _Laminaria_ sp. by BS or SC can change the composition of chemical groups in volatile compounds. In addition, the chemical groups of volatile compounds are distinct in BS and SC because these two groups are in the positive and negative axes of PC2, respectively. Based on the loading plot (Figure 5B), ketones in BS and alcohols in SC primarily cause the difference. As shown in Table 2, after fermentation, BS acquired higher ketone content than SC, whereas SC obtained higher alcohol content than BS.  
Another PCA was conducted to evaluate the correlation between a single volatile compound and the type of fermentation (Figure 6). PC1 and PC2 explained 55.6% and 29.9%, respectively, of the total variance in the dataset (Total: 85.5%). Consistent with Figure 5, the volatile compound compositions of BS and SC are differentiated from the unfermented _Laminaria_ sp. (Figure 6A). Moreover, based on the loading plot (Figure 6B), acetoin (i.e., 3-hydroxy-2-butanone) and 2,3-butanediol are positively correlated with BS, and 1-heptanol and 1-octanol are positively correlated with SC, thereby causing the difference in volatile compounds between the two fermented _Laminaria_. This finding is consistent with that shown in Figure 5, i.e., the difference between BS and SC is associated with the ketone and alcohol family.  
As shown in Table 2, acetoin accounts for the highest content (63.4%) in the ketone family from BS fermentation, followed by 1-heptanol (41.1%) and 1-octanol (20.5%) in the alcohol family from SC fermentation. On the contrary, in the third quadrant of the score plot (Figure 6A), the unfermented group and fermentation with lactic acid bacteria (LA, LB, and LC) are in the negative axis of PC1 and PC2. This finding indicates that lactic acid bacteria may not significantly modify the composition of volatile compounds as compared with the unfermented group. Based on the loading plot (Figure 6B), (E)-2-heptanol shows a higher correlation with the unfermented group and fermentation with lactic acid bac  
Figure 5: Principal component analysis plots of chemical groups of the volatile compounds in the brown seaweed _Laminaria_ sp. fermented by various microorganisms: (**A**) score plot (**B**) loading plot. UF: unfermented; BS: _B. subtilis_; SC: _S. cerevisiae_; LA: _Lb. acidophilus_; LB: _Lb. delbrueckii_ subsp. _bulgarius_; LC: _Lb. casei_. Sulfur-conta, sulfur containing compounds; benz, benzene derivatives.  
teria. Furthermore, (E)-2-heptenal was significantly reduced from 1179.00 to 538.71 and 429.48 \(\upmu\)g/L by fermenting with BS and SC, respectively (Table 2). In addition, (E)-2-heptenal contents were significantly lower in BS and SC fermentation than in lactic acid bacteria fermentation (Table 2). This finding may support the result that the groups of lactic acid bacteria and BS/SC are positioned on different quadrants in PCA.  
Therefore, according to the PCA (Figures 3-6), fermenting _Ulva_ sp. or _Laminaria_ sp. with BS or SC can modify the composition of volatile compounds compared with unfermented seaweeds. These results can be supported by Tables 1 and 2. Volatile and non-volatile compounds can contribute to the sensory characteristics of foods, which may further affect consumer preference [36; 37; 38]. Hence, GC-O was applied to evaluate the odor description and intensity of the fermented seaweeds.