Synergistic interactions between the genetically modified bacterial polysaccharide P2 and carob or konjac mannan.
Rheological studies have confirmed that the bacterial polysaccharide P2, a genetically modified variant of the Acetobacter xylinum polysaccharide acetan, undergoes synergistic gelation with either of the plant polysaccharides carob or konjac mannan. X-ray fibre diffraction data shows that P2 can form a 5-fold helical structure of pitch 4.7nm and an axial rise per disaccharide repeat of 0.92nm. Optical rotation data demonstrate that P2 undergoes a coil-helix transition in solution and that deacylation enhances the stability of the helical structure in solution. Studies made on mixtures prepared at different temperatures and ionic strengths suggest that denaturation of the P2 helix favours interaction and gelation. Deacetylation of P2 enhances gelation. X-ray diffraction data for oriented fibres prepared from deacetylated P2-konjac mannan mixed films reveal a 6-fold helical structure of pitch 5.54nm with an axial rise per disaccharide repeat also of 0.92nm. This mixed helix provides direct evidence for binding between the two polysaccharides. P2 contains two sites of acetylation: one on the backbone and one on the sidechain. The former site of acetylation inhibits helix formation for P2. It is suggested that this site of acetylation also inhibits formation of the mixed helix, explaining the enhanced gelation of mixtures on deacetylation.
Ridout
Michael
M
Institute of Food Research, Food Material Science, Norwich Research Park, Colney, Norwich NR4 7UA, UK.
Cairns
Paul
P
Brownsey
Geoffrey
G
Morris
Victor
V
D031056:Amorphophallus; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D005685:Galactans; D008351:Mannans / Q000737:chemistry*; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000737:chemistry; D053149:Plant Gums; D011134:Polysaccharides / Q000737:chemistry*; D011135:Polysaccharides, Bacterial / Q000737:chemistry*; D011189:Potassium Chloride; D013816:Thermodynamics; D014312:Trisaccharides / Q000737:chemistry; D014961:X-Ray Diffraction
D005685:Galactans; D008351:Mannans; D009844:Oligosaccharides; D053149:Plant Gums; D011134:Polysaccharides; D011135:Polysaccharides, Bacterial; D014312:Trisaccharides; D011189:Potassium Chloride; C017471:locust bean gum