Changes in aroma of itohiki-natto during refrigeration

Abstract

The changes in aroma compounds in itohiki-natto (a Japanese food made from fermented soybeans) during refrigeration were examined by the following methods because the smell was known to change under refrigeration. Itohiki-natto samples were stored in a refrigerator for a week and then aroma compounds were extracted by the simultaneous steam distillation extraction method, concentrated, analyzed by gas chromatography-olfactometry and gas chromatography-mass spectrometry. Several low-molecular-weight fatty acid esters, pyrazines, and lowmolecular-weight fatty acids were detected as the main aroma compounds. After a week of refrigeration, the aroma associated with the low-molecular-weight fatty acid esters tended to weaken, the aroma associated with pyrazines and low?molecular-weight fatty acids tended to become stronger. The main aroma compounds of itohiki-natto manufactured in the laboratory were extracted by solid-phase microextraction, and analyzed by gas chromatography and gas chromatography-mass spectrometry. The aroma compounds derived from soybeans and lowmolecular-weight fatty acid esters produced during fermentation decreased, and the aroma compounds derived from the pyrazines and low-molecular-weight fatty acids produced during the fermentation increased as the period of refrigeration was lengthened.