Identification of volatile compounds of kombu (Laminaria spp.) and their odor description

Kombu (edible Japanese kelp) is a well-known dietary source of iodine and minerals. This is the first report to our knowledge on the identification of the volatile iodine compounds, of kombu. The materials for this experiment were three kinds of dried kelp : 'Ma kombu' (Laminarin japonica Areschoug), 'Rishiri kombu' (Laminaria ochotensis Miyabe) and 'Mitsuishi kombu' (Laminaria angustata Kjellman). Each kombu was wild and harvested in Hokkaido in 1999, dried in the sun on the ground. Volatiles of kombu were collected using dynamic headspace sampling (DHS) method. In addition, volatiles were isolated by the method of simultaneous distillation and extraction under reduced pressure (SIDE). Volatiles were identified by a capillary GC-MS. Four iodides (2-iodopropane, 1-iodopropane, 1-iodopentane and 1-iodooctane) were isolated from each sample by DHS. In DHS, the total number of identified volatile compounds of 'Ma kombu', 'Rishiri kombu' and 'Mitsuishi kombu' were 49, 47 and 41, respectively. The odor description of volatile compounds was investigated using GC equipped with a headspace sampler and a sniffing port, Only 1-iodooctane had the odor in the four kinds of iodides. The odor description of 1-iodooctane was 'like dried kombu with laver' by GC-sniffing. The odor description of some compounds of dried 'Ma kombu' were (E)-2-heptenal (almond-like), nonanal (like dried outer peel of Citrus Unshiu), (E)-2-octenal (like dried kombu with soy sauce), (E)-2-nonenal (like kombu with sour), (E)-2-decenal (like stock made from kombu), 1-octen-3-ol (like dried kombu), (E)-2-octen-1-ol (like mushroom with citrus), (E)-2-nonen-1-ol (like salt-sweet preserve made of kombu). On the other hand, both of 1-iodopropane and 2-iodopropane of all samples were not isolated by SIDE. In the SIDE extracts, the total number of identified volatile compounds of 'Ma kombu', 'Rishiri kombu' and 'Mitsuishi kombu' were 53, 53 and 48, respectively. The Log odor unit value was calculated from the concentration and the odor threshold value. The following volatile compounds showed the Log odor unit larger than 2 in the 'Ma kombu' : 1-iodooctane, nonanal, (E)-2-nonenal, (E,Z)-2,6-nonadienal, 1-octen-3-ol, (E)-2-nonen-1-ol, (E,Z)-2,6-nonadien-1-ol, diacetyl and beta-ionone. It is supposed that the aroma of 1-iodooctane is one of the most important components of kombu aroma.