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Alginate is an anionic polysaccharide capable of forming insoluble particles with proteins. Hence, alginate has potential as a protein carrier. However, the role of physical properties of the polysaccharide, such as degree of polymerization (DP n ) and mannuronic/guluronic acid ratio, remains to be fully explored. Particle formation of a high and a low molar mass alginate (ALG) with β-lactoglobulin (BLG) at pH 2–8 depends on the average DP n (HMW-ALG: 1.59·10 3 ; LMW-ALG: 0.23·10 3 ) and the mannuronic/guluronic acid ratio (1.0; 0.6) as supported by using ManA 6 and GulA 6 as models. Dynamic light scattering (DLS) showed that particles of BLG with either of the two ALGs have essentially the same hydrodynamic diameter ( D H ) at pH 3 and 2, while at pH 4 particles of LMW-ALG/BLG have larger D H than of HMW-ALG/BLG. At pH 5–8 no significant particle formation was observed. ManA 6 did not form insoluble particles at pH 2–8, while GulA 6 formed insoluble particles, albeit only at pH 4. K d was approximately 10-fold higher for LMW-ALG/BLG than HMW-ALG/BLG and 3 orders of magnitude higher for an alginate trisaccharide/BLG complexation as determined by isothermal titration calorimetry (ITC). The alginate trisaccharide did not form insoluble particles with BLG at pH 3 and 4, though interaction still occurred. Δ H app and molar stoichiometry of BLG in the complexes with the two ALGs differed by a factor of 7, as did their DP n , which thus affected the interaction strength, but not the BLG content. At pH 4 the BLG content doubled in the particle due to BLG dimerization. The findings emphasize the importance of DP n , mannuronic/guluronic acid ratio and pH in formulations containing alginate/whey protein particles. [ABSTRACT FROM AUTHOR]

Casein-casein interactions can be very useful for tuning structural and physical properties of mixed casein micelles for food and biotechnology applications, particularly in the dairy industry. The present work focuses on the structures of mixed micelles formed by stepwise addition of a micellar β-casein solution to either 0.05 or 0.3 mM κ-casein, i.e. below or above the critical micellar concentration (CMC) of κ-casein, respectively. Insight into the thermodynamics of this mixed micellization was achieved using isothermal titration calorimetry (ITC), which indicated a less favorable enthalpy of formation and a downward shift of the CMC of mixed micelles with 0.3 mM κ-casein. Hydrophobic interactions are the main driving force behind the mixed micellization as probed by using pyrene, a hydrophobic fluorophore. Structural characterization by dynamic light scattering (DLS) and small angle X-ray scattering (SAXS) revealed that addition of micellar β-casein to 0.05 mM κ-casein oligomers caused strong perturbation and formation of smaller micelles compared to when added to 0.3 mM κ-casein in micellar state. Thus, association of β-casein with κ-casein in these two different physical forms of loosely interacting oligomers and micelles, respectively, can modulate formation of mixed micelles with regard to structural properties such as shape, size and molecular packing (compactness). Image 1 • β-/κ-casein interactions observed by thermodynamic and structural characterization. • Critical micelle concentration β-/κ-casein mixed micelles was determined. • Addition of β-casein changed β-/κ-casein mixed micelles compactness. • Tunable size and shape of β-/κ-casein mixed micelles. • Microenvironment polarity changes indicated different types of micelles was formed. [ABSTRACT FROM AUTHOR]