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Investigation of molecular interactions between β-lactoglobulin and sugar beet pectin by multi-detection HPSEC

Phoebe X. Qi, Hoa K. Chau, Marshall L. Fishman, Edward D. Wickham, Arland T. Hotchkiss
Carbohydrate polymers 2014 v.107 pp. 198-208
sugar beet, mixing, pectins, biopolymers, polymerization, hydrodynamics, dissociation, gel chromatography, pH, ionic strength, heat treatment, molecular weight, binding capacity, beta-lactoglobulin
Molecular interactions between β-lactoglobulin (β-LG) and sugar beet pectin (SBP) were studied using online multi-detection high performance size exclusion chromatography (HPSEC) at neutral pH and 50mM ionic strength. The hydrodynamic properties of various interacting polymer fractions were characterized in detail and compared with those of β-LG and SBP. Results showed that ∼6.5% (w/w) of native dimeric β-LG molecules formed complexes with over 35% SBP molecules of varying sizes, 800, 110 and 75kDa. Although the β-LG molecules bind to SBP molecules of all sizes and shapes, they tend to favor the intermediate (110kDa) and small sized (75kDa) SBP molecules. All resulting complexes possess altered shapes and hydrodynamic properties when compared to unbound SBP and β-LG. About half of the interacting β-LG (∼3.5%) molecules were thought to bind to a small amount of non-covalently bound feruloyl groups, possibly present in SBP. When pre-heat treated β-LG and SBP were combined, more than 16% of β-LG formed complexes with at least 45% of SBP molecules of varying sizes, Mw∼750–800, 110, and 55–80kDa. The complexes formed between β-LG aggregates and/or oligomers and the large SBP molecules (750–800kDa) adopt the shape of β-LG aggregates, random coil. Both groups of complexes formed between β-LG intermediate (110kDa) and small sized (55–80kDa) SBP take on the shape of rigid rod. It was speculated that half of the interacting heat-treated β-LG molecules (∼8%) are complexed with non-covalently bound feruloyl groups in SBP.