Volatile Compounds of Chonggugjang Prepared by Different Fermentation Methods and Soybean Cultivars

발효방법 및 대두품종을 달리한 청국장의 향기성분

This study was attempted to develop technique of masking the pungent odor of chonggugjang using two-stage fermentation method with mixed pure cultures. Cooked soybeans were fermented with Lactobacilli or Aspergillus oryzae at $38^{\circ}C$ for 36 hrs, and then re-fermented with Bacillus subtilis for 12 hrs. The volatile compounds of chonggugjang were obtained with a SDE(Simultaneous steam Distillation and solvent Extraction) system and the extracts were identified by GC and GC-MS. The experimental results revealed the presence of 35 volatile compounds in control chonggugjang(only Bacillus subtilis inoculation). Among them, the major volatile compounds were 2,5-dimethyl pyrazine, 2,3,5-trimethyl pyrazine and 2-methyl pyrazine. Twenty-nine kinds of volatile compounds were in chonggugjang prepared by two-stage fermentation method with Lactobacilli and Bacillus subtilis(II), and major volatile compounds were identified to be 2,3,5-trimethyl pyrazine and 2,5-dimethyl Pyrazine. In chonggugjang(Asp. oryzae and then Bacillus subtilis inoculation(III)), the contents of hexadecanoic acid and 2-methyl pyrazine were patricularly high and the main components of chonggugjang fermented with rice straw(IV) were 2,5-dimethyl pyrazine, 2,3,5-trimethyl pyrazine etc. In conclusion, the flavor compounds such as 2, 5-dimethyl pyrazine, 2,3,5-trimethyl pyrazine and 2-methyl pyrazine were increased by the inoculation of Lactobacilli or Asp. oryzae, where as unpleasant odor components-butyric acid and valeric acid were decreased. Compared with volatile compounds of chonggugjang made from different soybean cultivars, the flavor compounds (2-methyl pyrazine 2,5-dimethyl pyrazine 2,6-dimethyl pyrazine 2,3-dimethyl pyrazine 2-acetyl pyrazine 2,3,5-trimethyl pyrazine 2-ethyl-3,5-dimethyl pyrazine) of chonggugiang prepared with Sinpaldalkong were high.

발효방법에 따른 청국장의 휘발성 성분을 비교 조사하기 위해 증자대두에 Bacillus subtilis를 접종시킨 시험구(I), 1차 종균으로서 Lactobacilli(ll) 혹은 Aspergillus oryzae(III)를 접종시켜 소정시간 발효후 Bacillus subtilis를 추가 접종시킨 시험구, 그리고 볏짚을 접종원으로 한 시험구(IV)의 청국장제품을 각각 연속증류추출장치를 사용하여 휘발성 성분을 추출 농축하고 GC와 GC/MS를 이용하여 휘발성 성분을 분석 동정하였다. 그 결과 Bacillus subtilis 단용 발효구(I)와 볏짚을 접종원으로 사용한 시험구(IV)에서 각각 35종과 46종의 휘발성 성분이 검출되었고 Lactobacilli처리구(II)에서는 29종의 휘발성 성분이 검출되었는데 시험구(I), (IV)에 비해 향미성분으로 알려진 2,3,5-trimethyl pyrazine, 2,5-dimethyl pyrazine 등의 함량이 각각 2.2배, 1.5배 증가되었다. 또한 Asp. oryzae처리구(III)에서는 총 36종의 휘발성 성분이 분리 동정되었고 이들 성분 중에서 hexadecanoic acid, 2-methyl pyrazine성분이 많이 검출된 반면 청국장의 불쾌취로 알려진 butyric valeric acid는 검출되지 않았다. 대두 품종별로 제조한 청국장의 휘발성 성분을 비교 검토한 결과 신팔달콩을 원료대두로 사용한 시험구의 청국장이 향미성분은 증가한 반면 불쾌취 성분은 감소되었다.