###### Abstract  
Seaweeds have a variety of biological activities, and their aromatic characteristics could play an important role in consumer acceptance. Here, changes in aroma compounds were monitored during microbial fermentation, and those most likely to affect sensory perception were identified. _Ulva_ sp. and _Laminaria_ sp. were fermented and generally recognized as safe microorganisms, and the profile of volatile compounds in the fermented seaweeds was investigated using headspace solid-phase microextraction with gas chromatography-mass spectrometry. Volatile compounds, including ketones, aldehydes, alcohols, and acids, were identified during seaweed fermentation. Compared with lactic acid bacteria fermentation, _Bacillus subtilis_ fermentation could enhance the total ketone amount in seaweeds. _Saccharomyces cerevisiae_ fermentation could also enhance the alcohol content in seaweeds. Principal component analysis of volatile compounds revealed that fermenting seaweeds with _B. subtilis_ or _S. cerevisiae_ could reduce aldehyde contents and boost ketone and alcohol contents, respectively, as expected. The odor of the fermented seaweeds was described by using GC-olfactometry, and _B. subtilis_ and _S. cerevisiae_ fermentations could enhance pleasant odors and reduce unpleasant odors. These results can support the capability of fermentation to improve the aromatic profile of seaweeds.  
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seaweeds are frequently consumed fresh and dried; however, seaweeds are not normally ingested in the unprocessed form in Western societies, where seaweeds remain of minor importance in spite of their nutritional benefits [6]. For example, the ingestion of red seaweed _Bangia fuscopurpurea_ potentially reduces the risk of cardiovascular and chronic metabolic diseases, but its fishy malodor may limit consumers' acceptance [7]. Food sensory properties can play an important role in consumers' preferences and acceptance, of which the aroma compound is of prime importance [8]. Consequently, the identification of seaweed volatile compounds has drawn increasing attention for enhancing their application potential in food [3; 9].  
Microbial fermentation is often used to improve/enhance the sensory quality of food, such as cereals, meats, vegetables, and dairy foods, by removing undesirable off-flavors and/or generating new aroma compounds [10]. Recently, the application of microbial fermentation in removing undesirable odors in seaweeds has drawn increasing attention. [PERSON] et al. [11] indicated that the inoculation of the fungus _Aspergillus oryzae_ could decrease isovaleric acid and allyl isothiyanate and reduce the peculiar smell of seaweed kelp extracts. In addition, the co-fermentation of _Bacillus subtilis_ (BS) and _Lactobacillus plantarum_ of the microalga _Spirulina_ could reduce off-odors and produce creamy flavor compounds, such as acetoin and ethyl lactate [12]. However, research on sensory profiles of seaweeds during fermentation remains limited, not to mention that there are thousands of seaweed species.  
Therefore, the aroma compound profiles of seaweeds should be investigated during microbial fermentation to promote the development of new products and to widen the application of seaweeds in food or beverage sectors. This study aimed to qualitatively and quantitatively characterize the volatiles and odor-active compounds in the green seaweed _Ullu_ sp. and brown seaweed _Laminaria_ sp. fermented with various microorganisms using headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) and GC-olfactometry (GC-O). Consequently, the changes in aroma compounds were monitored during microbial fermentation, and those most likely to impact sensory perception were identified.