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Change in the composition and enzyme activity of culturable lactic acid bacteria in Nuruk during fermentation at different temperatures

온도를 달리한 누룩 발효 기간별 배양 유산균 변화 및 분리 유산균들의 효소 활성

  • Nam, Kang (Department of Food Science and Technology, Chonbuk National University) ;
  • Lee, Nam Keun (Research Center for Industrial Development of Biofood Materials, Chonbuk National University) ;
  • Yum, Eun-Ji (Department of Food Science and Technology, Chonbuk National University) ;
  • Kim, Yong-Sik (Research Center for Industrial Development of Biofood Materials, Chonbuk National University) ;
  • Kim, Dae-Hyuk (Department of Molecular Biology, Chonbuk National University) ;
  • Yeo, Soo-Hwan (Fermentation and Food Processing Division, Department of Agrofood Resources, Rural Development Administration) ;
  • Jeong, Yong-Seob (Department of Food Science and Technology, Chonbuk National University)
  • 남강 (전북대학교 식품공학과) ;
  • 이남근 (바이오식품소재개발 및 산업화연구센터) ;
  • 염은지 (전북대학교 식품공학과) ;
  • 김용식 (바이오식품소재개발 및 산업화연구센터) ;
  • 김대혁 (전북대학교 분자생물학과) ;
  • 여수환 (농촌진흥청) ;
  • 정용섭 (전북대학교 식품공학과)
  • Received : 2015.10.08
  • Accepted : 2015.11.11
  • Published : 2015.12.30

Abstract

The microbial composition in Nuruk, a Korean cereal fermentation starter, is a critical factor for the quality and organoleptic properties of traditional alcoholic beverages. This study was aimed at monitoring the compositional change and enzyme activity of culturable lactic acid bacteria (LAB) in two types of Nuruk fermented at different temperatures. All culturable LAB were isolated at various time points (0, 3, 6, 10, 20, and 30 days) and identified by 16S rRNA sequencing. In traditional Nuruk type A (TN-A), which was fermented at $36^{\circ}C$, the population of total culturable LAB during the fermentation period was between $10^4$ and $10^5$ log CFU/mL. On the other hand, the LAB population in traditional Nuruk type B (TN-B) fermented at $45^{\circ}C$ (primary fermentation for 10 days) and $35^{\circ}C$ (secondary fermentation for 20 days) was $10^2$ log CFU/mL; however, these bacteria could not be detected after 6 days. Major LAB strains were identified in both Nuruk types: (1) from the MRS-culture of TN-A, Pediococcus pentosaceus at 3-30 days; (2) from MRS-culture of TN-B, P. pentosaceus at 3 days and Enterococcus hirae at 6 days. The protease activities of the dominant LAB isolated from the TN-A and TN-B cultures were within the ranges of 0.64~1.03 mg/mL and 0.74~0.81 mg/mL (tyrosine content), respectively, whereas the ${\alpha}$-amylase activities were 0.75~0.98 mg/mL and 0.78~0.79 mg/mL (amylose content), respectively.

발효 온도를 달리한 전통방식으로 제조된 두 가지 형태(TN-A와 TN-B)의 누룩들로부터 발효 기간별 배양된 유산균 총균수, 유산균 종들의 변화 및 분리된 유산균들의 효소활성을 비교하였다. TN-A의 유산균 총균수는 $10^4{\sim}10^5$ log CFU/mL로 발효 3일차부터 발효 기간에 관계없이 유지되었고, TN-B에서는 발효 6일차까지 $10^2$ log CFU/mL로 유지되다가 6일차 이후 유산균이 검출되지 않는 특징을 보였다. 유산균 종들의 변화에 있어서, TN-A는 발효 3일차에 우점종 유산균으로 나타난P. pentosaceus 종이 발효 종료 시점이 30일차 까지 우점하고 있음을 확인할 수 있었고, TN-B는 발효 3일차와 6일차에 각각 P. pentosaceus와 E. hirea로 나타나 유산균이 검출된 발효 기간까지 TN-A 보다는 많은 변화를 보였다. TN-A와 TN-B으로부터 분리된 유산균들의 효소 활성은 단백질분해효소와 당화효소 활성을 분석하였다. 단백질분해효소평가는 티로신 생성량으로, 당화효소 활성은 아밀로스 분해에 따른 아밀로스 잔여 함량으로 평가한 결과, 분리된 유산균(9종)들은 0.49~0.89 mg/mL의 티로신 생성 범위의 단백질분해 활성과 0.64~0.79 mg/mL의 아밀로스 분해 활성 범위를 보였고, 유산균들 중 가장 높은 단백질분해효소와 당화효소 활성을 보이는 균주는 각각 P. acidilactici와 L. sakei로 확인되었다. 이상의 결과들은 온도를 달리하여 전통적인 방법으로 누룩을 제조하였을 시 누룩 내에 유산균들을 조절할 수 있음을 시사한다. 이를 토대로 향후 많은 연구들이 진행된다면, 누룩관련 제품에 유산균들에 의해 만들어지는 산미와 풍미를 향상 시킬 수 있는 전통적인 누룩제조가 가능할 것으로 판단된다.

Keywords

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