Odor-active compounds were identified by n-alkanes linear retention indices (C5–C18) on UA-1 and UA-5 columns and with odor quality. Most of the odor-active compounds were confirmed by retention indices. Library mass spectra and some standard compounds were also used. The odor-active compounds were conclusively determined by the information collected from each test and analysis (Fig. 4). Furthermore, nasal impact frequency (NIF) was used to identify each odor compound separated from GC/FID/O system among odor compounds. Although previously two research groups proposed to calculate peak detection frequencies from odors perceived by a panel of 6–10 assessors to improve the reliability of aromagrams, NIF was calculated by the results from three assessors in this study due to lack of sample (total volume of the sample was 5 l). NIF indicates the detected odor frequency (%) at olfactory detection port by a panel of three assessors [20].