Suomeksi
Year of publication: 2011
Type: Theses
Research field: Food chemistry and composition- Food analytics Branch: Other
Reliable information on the solution properties of branched polysaccharides by the utilization of different analytical methods (polysaccharides, solution properties, chemical structure)
In Leena Pitkänen’s doctoral thesis, the effect of the chemical structure on the dilute solution properties of branched polysaccharides was investigated using size-exclusion chromatography (SEC) and asymmetric flow field-flow fractionation (AsFlFFF) with multiple-detection. The results of this thesis show that complementary approaches in the solution characterization of chemically heterogeneous polysaccharides are needed to comprehensively investigate macromolecular behavior in solution.
Cereal arabinoxylans, guar galactomannans, and dextrans produced by lactic acid bacteria are a structurally diverse group of branched polysaccharides with nutritional and industrial functions. Although isolated arabinoxylans as such are not used industrially, their role as a health-promoting dietary fiber component in the daily diet is well-known and widely studied. Galactomannans are used widely as thickeners and stabilizers in various food products such as dairy products, ice cream, desserts, and bakery items. Dextrans have various food and non-food applications. In the food industry, dextrans are used as gelling agents, thickeners, and emulsion stabilizers. In addition to above mentioned applications, all of these polysaccharides could be exploited more efficiently due to their abundant and renewable nature. The accurate knowledge on the chemical structures and physical properties of polysaccharides, however, must be obtained before development of new applications.
The chemical characterization of studied polysaccharides indicated differences in their chemical structures. The solution characterization of arabinoxylans, enzymatically modified galactomannans, and dextrans revealed the presence of aggregates in aqueous polysaccharide solutions. In the case of arabinoxylans and dextrans, the comparison of molar mass data from aqueous and organic SEC analyses was essential in confirming aggregation, which could not be observed only from the peak or molar mass distribution shapes obtained with aqueous SEC. The AsFlFFF analyses gave further evidence of aggregation. Comparison of molar mass and intrinsic viscosity data of unmodified and partially debranched guar galactomannan, on the other hand, revealed the aggregation of native galactomannan. The arabinoxylan and galactomannan samples with low or enzymatically extensively decreased side unit content behaved similarly in aqueous solution: lower molar mass samples stayed in solution but formed large aggregates, whereas the water solubility of the higher-molar-mass samples decreased significantly. The solubility of dextrans with very high molar mass (> 1 000 000 g/mol) was low regardless of the differences in the fine structure.
