Complex coacervates of lactotransferrin and β-lactoglobulin.

Hypothesis: Oppositely charged proteins should interact and form complex coacervates or precipitates at the correct mixing ratios and under defined pH conditions.

Experiments: The cationic protein lactotransferrin (LF) was mixed with the anionic protein β-lactoglobulin (B-Lg) at a range of pH and mixing ratios. Complexation was monitored through turbidity and zeta potential measurements.

Coacervates of lactotransferrin and β- or κ-casein: structure determined using SAXS.

Lactotransferrin (LF) is a large globular protein in milk with immune-regulatory and bactericidal properties. At pH 6.5, LF (M = 78 kDa) carries a net (calculated) charge of +21.

Protein composition of different sized casein micelles in milk after the binding of lactoferrin or lysozyme.

Casein micelles with bound lactoferrin or lysozyme were fractionated into sizes ranging in radius from ∼50 to 100 nm. The κ-casein content decreased markedly and the αS-casein/β-casein content increased slightly as micelle size increased. For lactoferrin, higher levels were bound to smaller micelles.

Coacervates of lysozyme and β-casein.

Complexes are formed when positively charged lysozyme (LYZ) is mixed with negatively charged caseins. Adding β-casein (BCN) to LYZ leads to flocculation even at low addition levels. Titrating LYZ into BCN shows that complexes are formed up to a critical composition (x=[LYZ]/([LYZ]+[BCN]).