Volatile profile of khanom jeen, Thai fermented rice noodles, and the changes during the fermentation process

This study was carried out to determine the volatile compounds profile of khanom jeen (Thai fermented rice noodles) and the changes in the volatile compound composition during fermentation. Rice samples were collected at each step of the fermenting process. Identification and quantification of volatiles were performed by evaluating dynamic headspace with gas chromatography mass spectrometry. For khanom jeen, a total of 43 compounds were found. Among them, 2-methylpropanoic acid, 3-methylbutanoic acid, diacetyl, ethyl acetate, ethyl valerate, ethyl hexanoate, ethyl heptanoate, heptanal, octanal, nonanal, decanal, and 3-methylbutanal were identified as potent odourants based on their odour activity values. Most of the volatile compounds increased during the first 24-48 h of the rice fermentation process, except for some esters which increased thereafter during the sedimentation step. The concentrations of selected aromatic volatile compounds in khanom jeen were affected by the fermentation steps particularly 2-methylpropanoic acid and 3-methylbutanoic acid, which were not found in the raw material (broken rice). The amount of ethyl acetate in the water elimination process was found to be twice as much as in the first day of rice fermentation. The presence of straight-chain aldehydes changed only slightly during rice fermentation. However, the concentration of 3-methylbutanal increased substantially. The results indicated that the aroma of khanom jeen was affected by the fermentation process.