Microbiology and Biotechnology Letters (한국미생물·생명공학회지)

The Korean Society for Microbiology and Biotechnology (한국미생물·생명공학회)
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Physicochemical Properties of a Biopolymer Flocculant Produced from Bacillus subtilis PUL-A

Bacillus subtilis PUL-A로부터 생산된 Biopolymer 응집제의 물리화학적 특성

  • Ryu, Mi-Jin (Department of Food Science and Technology, Keimyung University) ;
  • Jang, Eun-Kyung (Traditional Microorganism Resources Center, Keimyung University) ;
  • Lee, Sam-Pin (Department of Food Science and Technology, Keimyung University)
  • 류미진 (계명대학교 자연과학대학 식품가공학과) ;
  • 장은경 (계명대학교 전통미생물자원개발 및 산업화연구센터) ;
  • 이삼빈 (계명대학교 자연과학대학 식품가공학과)
  • Published : 2007.09.28
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Abstract

Soybean milk cake (SMC) was used for the solid-state fermentation by Bacillus subtilis PUL-A isolated from soybean milk cake. In the presence of 5% glutamate the maximum production of biopolymer (59.9 g/kg) was performed by fermentation at $42^{\circ}C$ for 24 hr. The recovered biopolymer was consisted of 87% $\gamma$-polyglutamic acid with molecular weight of $1.3{\times}10^6$ dalton and other biopolymer. The biopolymer solution showed the great decrease in consistency below pH 6.0, regardless of the molecular weight of PGA. Biopolymer solution has a typical pseudoplastic flow behavior and yield stress. The consistency of biopolymer solution was greatly decreased by increasing heating time and temperature in acidic condition compared to the alkaline condition. In kaolin clay suspension, the flocculating activity of biopolymer was the highest value with 15 mg/L biopolymer and 4.5 mM $CaCl_2$, but decreased greatly with $FeCl_3$. The flocculating activity of biopolymer was maximum at pH5, but decreased drastically by heating at $60{\sim}100^{\circ}C$. In particular, biopolymer with native PGA showed the efficient flocculating activity compared to that of modified biopolymer containing low molecular weight of PGA.

비지로부터 분리한 Bacillus subtills PUL-A 균주를 이용한 비지발효물로부터의 biopolymer flocculant 생산은 glutamate 함량이 5% 첨가한 후 $42^{\circ}C$에서 24시간동안 발효하는 경우에 PGA 생산량은 52.2g/kg으로 최대를 나타내었다. 부분 정제된 biopolymer flocculant의 PGA의 함량은 87%이었으며, 분자량은 $1.3{\times}10^6$ dalton 이상을 나타내었다. PGA의 pH 변화에 따른 점조도는 pH 6을 기준으로 산성 쪽으로 갈수록 급격하게 감소하였으나, 분자량의 변화는 거의 나타나지 않았다. Bioflocculant의 유동특성은 농도가 증가할수록 전단속도가 증가되어 전형적인 의가소성 흐름특성을 나타내었으며, 항복력도 증가하였다. Bioflocculant 용액의 점조도 값은 pH가 높을수록 열에 상당히 안정하였으나 열처리온도 및 시간이 증가할수록 pH에 따라 급격하게 감소하였다. Kaolin clay suspension을 이용한 응집활성에서 bioflocculant의 농도가 15 mg/L 일 때 최대 응집활성을 나타내었으며, 응집활성은 $Ca^{2+}$을 첨가할 때 가장 높게 증가하였으며 최적 농도는 4.5mM로 나타났다. 그러나 3가 양이 온인 $Fe^{3+}$을 첨가할 경우는 응집활성이 급격하게 감소하였다. 응집활성은 pH 5에서 가장 높게 나타났으며, $60{\sim}100^{\circ}C$에서 열처리함에 따라 응집활성은 급격하게 감소하였다. 또한 저분자량의 PGA보다는 native 고분자량의 PGA가 응집활성에 매우 효과적인 것으로 나타났다.

Keywords

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