## 3 Results
### Volatile Compounds  
Table 3 lists the volatile compounds identified and quantified in raw, blanched, steamed, boiled, and baked \(L\). _japonica_. The results were the arithmetic mean \(\pm\) standard deviation of three samples. The results show that eight flavor substances were detected in raw \(L\). _japonica_. Among them, the content of 1-octen-3-one was the most abundant, reaching 48.32%, followed by the content of 1-methoxy-2-propyl acetate (21.33%) and 1,4-di-iso-propylhphalene (21.33%). However, only four flavors were detected in the kelp after the blanched treatment, and compared with the untreated kelp, all of these four flavors were newly generated. Among them, the content of trans-\(\beta\)-ionone and benzaldehyde was the most abundant, reaching 37.80% and 35.06%. It is worth noting that trans-\(\beta\)-ionone is an important carotenoid derivative [53] that can be produced by thermal degradation or by enzymatic reactions [54], so it could be speculated that carotenoids (possibly fucoxanthin) from kelp were produced by degradation during blanching processing because blanching did significantly reduce the fucoxanthin content in kelp (from 1.12 to 0.44), as can be seen in Table 2. The steamed kelp had more flavor substances, the same as the raw kelp, both with 1-methoxy-2-propyl acetate and 1-octen-3-one flavor substances. In addition, nine flavor substances were newly formed after steaming. Of the nine newly generated flavor substances, two were identical to those found in blanched kelp, namely benzaldehyde and acetophenone. Benzaldehyde was the most abundant flavor compound in steamed kelp (24.23%), similar to the blanched kelp. Benzaldehyde could be produced by derivation from amino acids [55] or by oxidation of trans-cinnamic acid [56].There were seven flavor substances in the boiled kelp, among which 1-methoxy-2-propyl acetate (66.21%) and 2-heptenal (Z)-(7.91%) were the same as that in the raw kelp, but it was the same as that in the steamed kelp, where both produced styrene. The 1-Methoxy-2-propyl acetate content increased from 21.33% s to 66.21%, indicating that cooking significantly increased the ester content of kelp. This might be due to the esters generated by decarboxylation and substitution of lipids in kelp during the cooking process [57]. Compared with raw kelp, baked kelp showed the most significant changes in flavor compounds. A total of 30 flavor compounds were detected in the baked \(L\). _japonica_, among which 4 were the same as those in the raw kelp. In addition, unlike the raw kelp, the naphthalene 1,2-dihydroxy-1,1,6-trimethyl- was the same as the blanched kelp, and furan, 2-pentyl-, styrene, and the phenol 3,5-bis(1,1-dimethylethyl)- were the same as the steamed kelp. Styrene and 2\({}^{\prime}\)3\({}^{\prime}\)A\({}^{\prime}\)trimethoxyacetophenone in boiled kelp were also detected in baked kelp but at lower levels. Furthermore, the content of decanal and pentadecane were the most abundant at 21.87% and 21.86%, respectively. Some identified compounds were also found in previous works such as that of [PERSON] et al. [58] and [PERSON] et al. [59]. In general, all cooking  
methods induced an increase in the content of aldehydes compared to raw kelp. A similar phenomenon was found by [PERSON] et al. (2016); i.e., longer heating times induced a significant release of several aldehydes from seaweed (_Laminaria digitata_) suspensions. This might be due to the oxidation of fatty acids ([PERSON] et al., 2016) in the kelp due to heating and the formation of unsaturated aldehydes (e.g., benzaldehyde in blanching and benzaldehyde and (E)-2-heptenal in steaming) and saturated aldehydes (decanal in baking), all of which were associated with a \"fatty\" odor ([PERSON] et al., 2016). In addition, the concentration of aldehydes in some processed foods might increase after heat processing due to chemical reactions that occur under high-temperature heating conditions, such as degradation of amino acids or carbohydrates ([PERSON] et al., 2016).