To investigate the relationship between the structure and the emulsifying activity of a lipopolysaccharide biosurfactant, emulsan from Acinetobacter calcoaceticus RAG-1, the emulsan samples having various structure were prepared such as different fatty acid contents and composition, and different carbohydrate backbone structure under different culture conditions such as kind of carbon source, temperature, growth stage, specific growth rate, inhibition of fatty acid biosynthesis, and combination of above conditions, and the structure of the purified emulsan samples were determined using GC and GC-MS. The fatty acid, only hydrophobic moiety of emulsan, partially influenced the emulsifying activity. The emulsifying activity was proportional to the fatty acid contents until 8%, and then reached plateau above 8%. The composition of fatty acid did not play an important role in their emulsification. Effect of protein moiety of emulsan was confirmed by comparing the emulsifying activity after removal of protein by hot-phenol method, and no effect was found on the emulsification. In the study of carbohydrate backbone structure, emulsan was found to have a branched-structure rather than linear structure. The emulsifying activity of emulsan was proportionally increased as the branching degree of polysaccharide backbone increased. To decide the more important structural factor influencing the emulsifying activity, statistical analysis was performed by the fatty acid content and the branching degree of polysaccharide. It was concluded that the emulsifying activity of emulsan was more influenced by the branching degree rather than the fatty acid contents. It was, thus, suggested that the oil droplet could be more efficiently surrounded by highly branched polysaccharide backbone oil/water in emulsion system, resulting in the formation of more stable emulsion.
A novel biosurfactant producing strain was isolated and identified to Klebsiella oxitoca BSF-1 from Korean soil. The new biosurfactant, named as BSF-1, was a lipopolysaccharide (1,700-2,000 kDa) composed of carbohydrate (71.1%), fatty acid (1.1%), and removable protein (3.2%). The carbohydrate components were determined to be rhamnose, galactose, glucose, and glucuronic acid with a molar ratio of 3:1:1:1. In an aqueous solution, the hydrodynamic volume was 22.78 dl/g. It showed a relatively high emulsion stability (1.2-1.9 U/mg) though it did not much reduce the surface and interfacial tension. The viscosity reached 10 cp in the concentration of 5g/l. Considering the all above physico-chemical properties, a novel biosurfactant, BSF-1 was suggested to have a potential to apply for commercial use such as an additive for cosmetics.
Acinetobacter calcoaceticus RAG-1에서 생산되는 당지질계 고분자 생물계면활성제인 emulsan의 생물학적 구조변형 및 구조와 유화능간의 관계를 고찰하기 위해 서로 다른 여러가지 배양조건에서 emulsan을 생산하였다. 이때 배양조건들은 탄소원, 생장온도, 생장시기, 생장속도, 지방산 생합성 저해, 위 조건들의 조합등을 변화시켜 여러가지 구조의 emulsan이 생산되었다. Emulsan분자중 유일한 소수성부분인 지방산은 유화능에 어느정도 영향이 있는 것으로 나타났다. 즉, 전체 지방산 함량이 8%까지 증가함에 따라 유화능이 비례적으로 증가하였고, 그 이후 일정수준을 유지하였다. 지방산 조성은 유화능과 무관했다. 단백질 역시 유화능과 관계가 없었다. Emulsan의 3차원적 구조의 변형이 유화능에 큰 영향을 미친다는 사실을 통해 탄수화물 중합체의 구조연구를 수행하였다. Emulsan이 분지구조를 갖고 있다는 사실이 새롭게 밝혀졌으며, 더욱이 분지구조가 많을수록 유화능이 비례적으로 증가한다는 사실을 밝혀냈다. 유화능 결정에 있어서 가장 중요한 구조적 인자를 결정하기위해 통계적인 방법으로 지방산과 분지구조를 비교한 결과, 분지구조가 emulsan의 유화능을 결정하는데 더 중요한 인자임을 밝혀냈다.
새로운 당지질계 고분자 생물계면활성물질을 분리하기 위해, 토양으로부터 유화활성을 갖는 균주를 분리해 내었다. 생화학적 분석을 통해 Klebsiella oxitoca로 동정되었고, 생산되는 계면활성물질을 BSF-1으로 명명하였다. 이 물질은 분자량 1,700-2,000 kDa인 고분자 물질이였고 당 (71.1%), 지방산 (1.1%), 그리고 추출로 제거가 가능한 단백질로 구성된 당지질계 고분자 물질이었다. 구성당은 rhamnose, galactose, glucose 및 glucuronic acid가 약 3:1:1:1의 비율로 섞인 heteropolysaccharide였다. 수용액상에서의 부피 (hydrodynamic volume)은 22.78 dl/g였다. 비교적 높은 유화능 (1.2-1.9 U/mg)을 보였지만 장력감소는 적었다. 5 g/l의 농도에서 점도는 10 cp였다.
