Studies of Molecular Interactions between β-Lactoglobulin and Sugar Beet Pectin at Neutral pH by High Performance Size Exclusion Chromatography

Abstract

Foods that are rich in protein and other micronutrients such as bioactives and vitamins but low in sugar and fat may help mitigate the global obesity epidemic. Specialty ingredients can be fabricated to possess specific functions such as encapsulating bioactives through controlled assembly of protein and polysaccharide molecules. One of the most commonly used methods of combining proteins and polysaccharides into functional biopolymer particles is based on electrostatic attraction between oppositely charged groups under appropriate conditions(concentration, pH, ionic strength, and temperature etc.). In this work, interactions betweenβ-lactoglobulin(β-LG), a major milk protein, and sugar beet pectin(SBP), one of the most versatile polysaccharides, were investigated using online multi-detection High Performance Size Exclusion Chromatography(HPSEC) at neutral pH. The hydrodynamic properties of various interacting polymeric fractions were characterized in detail. Results showed that although nearly 6.5%(w/w) of native dimericβ-LG molecules formed complexes with∼35% SBP of varying sizes, 800, 110 and 75 kDa, they tend to favor the intermediate(110 kDa) and small sized(75 kDa) molecules. All resulting complexes possess altered shapes and hydrodynamic properties compared to the unbound SBP andβ-LG. Of the interactingβ-LG molecules, nearly half were believed to bind to a small amount of free ferulic acid in SBP. It was also demonstrated that pre-heating significantly increased the amount ofβ-LG involved in binding to both the feruloyl moieties(of SBP) as well as the free ferulic acid, which is a known antioxidant. This study established a molecular understanding of non-covalent interactions betweenβ-LG and SBP, and will aid the design of new types of interacting systems.