Spontaneous interaction between whey protein isolate proteins and lactoferrin: Effect of heat denaturation

Native lactoferrin (U-Lf) forms predominantly soluble complexes with native (U-WPI) or denatured (H-WPI) whey protein isolate proteins at all mixing ratios, forming weakly turbid solutions and charge neutrality at a Lf to WPI ratio of 2.0, w/w. This may be due to an asymmetrical charge spacing between the two interacting protein species, resulting in a weak interaction and soluble complexes. Denatured lactoferrin (H-Lf) strongly interacts with U-WPI or H-WPI, with highly turbid solutions formed at certain ratios. For H-Lf/U-WPI, maximum turbidity and charge neutrality was observed at a ratio of 2.0, w/w, with turbidity decreasing and zeta potential increasing either side of this ratio. H-Lf/H-WPI formed highly turbid solutions and neutral complexes at a ratio of about 2.0, w/w; however, the solution remained highly turbid at higher ratios despite the increasing charges of the complexes. Denaturation may make the proteins less flexible allowing desolvation leading to precipitation rather than coacervation.