Changes in the Key Aroma Compounds of Raw Shiitake Mushrooms (Lentinula edodes) Induced by Pan-Frying as well as by Rehydration of Dry Mushrooms.

Application of the aroma extract dilution analysis (AEDA) on an extract/distillate from raw shiitake mushrooms revealed 32 odorants among which 3-(methylthio)propanal (cooked potato), 1-octen-3-one and 1-octen-3-ol (both mushroom-like) showed the highest flavor dilution (FD) factors. An isotope enrichment experiment with raw shiitake tissue and either 13C18-linoleic acid or 2H4-1-octen-3-ol confirmed that both, 1-octen-3-ol and 1-octen-3-one are direct degradation products of the fatty acid, but it could be proven for the first time that the ketone is not formed by an oxidation of the alcohol. After pan-frying, 42 odor active compounds appeared among which 3 hydroxy 4,5-dimethylfuran 2(5H) one (savory), 1,2,4,5 tetrathiane (burnt, sulfury), 4 hydroxy-2,5 dimethylfuran 3(2H) one (caramel-like), phenylacetic acid (honey-like), 3 (methylthio)-propanal and trans 4,5 epoxy (E) 2 decenal (metallic) showed the highest FD factors. To get a deeper insight into their aroma contribution, 19 key odorants were quantitated in the raw shiitake and twenty-one in the pan-fried mushrooms by stable isotope dilution assays, and new methods for the quantitation of four sulfur compounds were developed. A calculation of odor activity values (OAV; ratio of concentration to odor threshold) showed that 1-octen-3-one was by far the most important odorant in raw shiitake. During pan-frying, in particular four aroma compounds were significantly increased, i.e., 4 hydroxy-2,5 dimethylfuran 3(2H) one, dimethyl trisulfide, 1,2,4,5 tetrathiane and 1,2,3,5,6-pentathiepane. The overall aroma profile of pan-fried shiitake could very good be mimicked by an aroma recombinate consisting of 15 reference aroma compounds in the concentrations determined in the pan-fried mushrooms. Further results showed that the sulfur compounds were even higher in rehydrated dry shiitake as compared to the pan-fried mushrooms.