Reduction of aldehydes with green odor in soy products during fermentation with Lycoperdon pyriforme and analysis of their degradation products

Soy products are rejected by Western consumers because of their green and beany off-aroma. The off-aroma profiles of typical soy products (soy drink and soy protein isolate) were analyzed and forty-five regions imparting green and beany odor impressions were perceived after application of direct immersion-stir bar sorptive extraction coupled with gas chromatography-mass spectrometry-olfactometry. After a fermentation of 28 h with Lycoperdon pyriforme the intensity of the off-aroma was reduced. Accordingly, thirteen and fourteen of the thirty-five quantified compounds were significantly decreased after fermentation of soy drink and soy protein isolate, respectively. The major off-aroma contributors, aldehydes, were reduced during fermentation and their degradation products were analyzed. The following bio-pathways were suggested (i) saturated aldehydes were reduced to the corresponding alcohols with increased odor threshold, leading to less intense sensorial perception, and (ii) di-unsaturated aldehydes did not form any odor-active substance in the volatile spectrum. Both of the phenomena explained the decreased sensorial perception of the off-aroma.