Using Surface Plasmon Resonance Technology to Screen Interactions Between Exopolysaccharides and Milk Proteins

Abstract

Surface plasmon resonance-based biosensors enable the interaction between biomolecules to be monitored in real time with a label-free assay format. In the present study, the technique was used to assess the interaction between exopolysaccharides (EPS) and different milk proteins. The EPS were derived from three homopolysaccharide (HoPS)-producing Lactobacilli strains; Lactobacillus sakei, Lactobacillus plantarum, and Lactobacillus salvarius. The purified milk proteins applied were β-casein, β-lactoglobulin, and κ-casein. The results show that the binding capacity depends on the pH and decreases with increasing pH. HoPS from L. salvarius and L. sakei provided the highest binding response and interacted with κ-casein at all the tested pH values, i.e. in the range 4.0−5.5, and with β-casein at pH 4.0−5.0. When examined at pH 4.0, only HoPS from L. salvarius and L. sakei interacted with β-lactoglobulin. Under the tested conditions, HoPS from L. plantarum showed always either a lower binding response or no binding at all compared with HoPS from L. salvarius and L. sakei.

Binding Interactions Between α-glucans from Lactobacillus reuteri and Milk Proteins Characterised by Surface Plasmon Resonance

“…A similar pattern was observed for gluc55730 ( Figure 2) at pH 5.0 and 5.5, but at pH 4.0 there were no signs of saturation of the surface under the association phase. This differs from the sensorgrams obtained previously for EPS from Lactobacillus sakei, Lactobacillus plantarum and Lactobacillus salvarius and milk proteins, 15 where the binding curves started to reach a plateau at the end of the association phase.…”

“…The gluc55730 thus interacted at pH 5.5; but no glucan binding, however, to native β-lactoglobulin was observed at pH 4.0. This was unexpected considering earlier data on HoPS binding, 15 showing relatively low binding of HoPS at pH 4.0 and none at pH 4.5-5.5 under the same conditions. The low binding levels of glucML1 and the lack of binding of gluc180 and glucA, however, are in agreement with the previous study 15 and may be due to the globular, rigid and hydrophobic structure of native β-lactoglobulin.…”

“…Binding between EPS and milk proteins can be monitored by surface plasmon resonance (SPR) analysis 15 involving immobilisation of the various milk proteins onto a sensor chip and passing EPS in solution over the sensor surface. When EPS binds to the protein a change in the SPR response is detected, which is proportional to the amount of bound EPS.…”

“…Even weak interactions can be detected over time by this technique. 15,16 SPR has been extensively applied in life science and drug discovery, but has also several applications in food science. 17 In relation to milk, SPR was used to quantify β-casein 18 , casein interactions, 19 and recently to describe casein-carrageenan 20 and milk proteinHoPS interactions, 15 respectively.…”

“…The interactions of HoPS from three Lactobacillus species with immobilised β-casein, β-lactoglobulin and κ-casein were previously monitored by SPR at pH 4.0-5.5 15 and found to be highly dependent on the bacterial strain, pH and the milk protein. In the present study, glucans from different strains of Lactobacillus reuteri (ATCC-55730, 180, ML1 and 121) of varying molecular weight, linkage types, and degree of branching 7,[21][22][23][24] were analysed for binding to native β-lactoglobulin, denatured β-lactoglobulin and κ-casein in the range pH 4.0-5.5 by using SPR.…”