Determination of compounds responsible for tempeh aroma

Tempeh is a fermented food, popular mainly in south-east Asia, but also among vegetarians worldwide. It is produced by fermenting soybean or other beans with Rhizopus strains and usually eaten deep-fried, steamed or roasted. The flavour of tempeh depends upon the fermentation time, beans used and the (eventual) frying process. Our goal was to identify compounds responsible for the unique aroma of fermented and fried soy tempeh. Gas chromatography-olfactometry (GC-O) with the aroma extract dilution analysis (AEDA) approach, was used to determine key odorants after 1 and 5 days of fermentation and subsequent frying. Comprehensive gas chromatography-mass spectrometry (GC × GC-ToF-MS) was used for their quantitation using stable isotope dilution analysis (SIDA) or standard addition (SA) methods. Odour activity values (OAV) were calculated for 19 out of 21 key odorants. Tempeh was fermented for 5 days and fried, and the main aroma compounds were found to be the following: 2-acetyl-1-pyrroline, (FD = 1024, OAV 1380), 2-ethyl-3,5-dimethylpyrazine (FD = 512, OAV 338), dimethyl trisulfide, (FD = 512, OAV 900), methional (FD = 512, OAV 930), 2-methylpropanal (FD = 512, OAV 311) and (E,E)-2,4-decadienal (FD = 512, OAV 455). The frying process induced the increase or appearance of the main key odorants in tempeh.