Volatile organic acids in freeze-dried Cheonggukjang were quantified using a stable-isotope dilution assay (SIDA) according to the fermentation period. Five organic acids, acetic acid, propanoic acid, 2-methylpropanoic acid, butanoic acid, and 3-methylbutanoic acid, were identified using solid-phase microextraction (SPME) in conjunction with gas chromatography-mass spectrometry (GC-MS). The contents of volatile organic acids in Cheonggukjang were highly dependent on the fermentation period and they increased during fermentation. Moreover, the branched-chained organic acids (namely 2-methylpropanoic acid and 3-methylbutanoic acid) were formed earlier and were present at much higher contents than the corresponding straight-chained organic acids during Cheonggukjang fermentation.
Bibliographical noteFunding Information:
This work was supported by the Korea Science and Engineering Foundation (KOSEF) grant funded by the Korea government (MOST) (No. M10510120003-06N1012-00310).
- Gas chromatography-mass spectrometry (GC-MS)
- Solid-phase microextraction (SPME)
- Stable-isotope dilution assay
- Volatile organic acid