## 3 Results and Discussion
### Sensory Evaluation of the Intensity of the Odor-Active Compounds in the Fermented seaweeds  
GC-O is considered as a major technique for analyzing the effect of volatile compounds on sensory characteristics, which has been applied to seaweeds [3]. The results of GC-O analysis for the unfermented and fermented _Ulva_ sp. are summarized in Table 3.  
A total of 22 odor-active compounds were detected, including six ketones, four aldehydes, four alcohols, one ester, one pyrazine, and six unidentified compounds. Among the pleasant odors, floral, sweet, and fruity were described. After fermentation with BS and SC, aromatic notes were enhanced, compared with the unfermented _Ulva_. For example, benzyl alcohol could contribute to floral and fruity aromas after BS and SC fermentation. Benzyl alcohol is described as flower, apple peel, and sweet aromas in Chinese bayberry [39], and it has been reported in many fruits [40]. In addition, 1-hexanol and 1-heptanol could provide extra floral/sweet and sweet aromas in the SC group, and the floral aroma of 6-methyl-5-hepten-2-one was enhanced in the BS group (Table 3). Notably, after fermentation with BS, 2,5-dimethylpyrazine is formed (Table 1), and it contributes to the nutty and roasted aromas in the fermented _Ulva_ sp. (Table 3). This odor description is consistent with the report of [PERSON] et al. [41], indicating that 2,5-dimethylpyrazine is the critical contributor to roasted peanut flavor in Oolong tea. According to [PERSON], [PERSON], [PERSON], and [PERSON] [35], 2,5-dimethylpyrazine  
Figure 6: Principal component analysis plots 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. _bulgaricus_; LC: _Lb. casei_. was found in several _Bacillus_-fermented soybean products. With regard to strong odor intensity, \(\beta\)-ionone (violet, floral) is the only compound that is described as having a strong and pleasant odor in all groups. Based on the report of [PERSON] et al. [42], \(\beta\)-ionone has a lower odor threshold (0.007 ppb) than 6-methyl-5-hepten-2-one (50 ppb) in water. This finding might indicate that the odor intensity of \(\beta\)-ionone is strong and greater than 6-methyl-5-hepten-2-one. In strengthening the pleasant odor of _Ulva_ sp. by fermenting with BS and SC, both fermentations can mitigate the unpleasant odors (Table 3). For example, the odor intensity of hexanal (fishy, grassy) was reduced in the BS- and SC-fermented _Ulva_ sp. suspensions. Described as caramelly, fried, and toasty, 5-Methylfurfural was not detected in the BS-fermented _Ulva_ sp. suspension by GC-O. These reductions are consistent with that shown in Table 1 in this study. BS and SC have demonstrated their application potential in improving pleasant odors and lightening unpleasant odors of _Ulva_ by fermentation. The results of the GC-O analysis for the unfermented and fermented _Laminaria_ sp. are outlined in Table 4. A total of 36 odor-active compounds were detected, including 7 ketones, 11 aldehydes, 8 alcohols, 1 acid, 1 ester, and eight unidentified compounds. Only three compounds, namely, \(\beta\)-ionone (violet, floral), benzaldehyde (fruity, sweet), and 1-octanol (waxy, citrus), were detected as pleasant odors in the unfermented _Laminaria_ sp. suspension. In addition, the pleasant odors could be strengthened in the _Laminaria_ suspension fermented with BS and SC. For example, 2,3-butanedione, described as yogurt and creamy, has shown a medium odor intensity in BS, whereas 1-heptanol, described as sweet, has shown a strong