Odor and flavor contribution of 2-pentyl pyridine to soy protein isolates

Total lipid extracts from two commercial soy protein isolates (SPI) were subjected to analyses by gas chromatography/olfaction by using capillary columns with stationary phases of three different polarities. With Kovats indices to identify the location of the odorous compounds on chromatograms produced with the same lipid extracts by gas chromatography/mass spectroscopy, the corresponding mass spectra of clearly distinguishable odors were examined. Compounds, tentatively identified by their mass spectra, were confirmed by retention times (on all three stationary phases), odor intensity, and odor description when compared with standards. Major odorous compounds identified included 2-methyl butyric acid methyl ester, hexanal, butyric acid, and 2-pentyl pyridine. Subsequent sensory analyses demonstrated that the mean levels of 2-pentyl pyridine found in two SPI (0.28 and 1.01 ppm), combined with its repulsive flavor profile (throat-catching and grassy in water) and extremely low flavor threshold level (0.000012 ppm), make it a major contributor to the undesirable flavor of SPI. Its mean contents in SPI were 23,333 and 84,167 times greater, respectively, than its flavor threshold. The level of hexanal was 112 and 201 times, respectively, above its flavor threshold, and the level of 2-pentyl furan in each SPI was 433 and 592 times, respectively, above its flavor threshold, which indicates that these two compounds make relatively minor contributions to the flavor of SPI.