Observation of salt-induced beta-lactoglobulin aggregation using sedimentation field-flow fractionation

Sedimentation field-flow fractionation (SdFFF) was applied in order to characterize particle sizes of beta-lactoglobulin aggregates induced by Ca2+ or Zn2+. Aggregation induced by Zn2+ was faster than that induced by Ca2+. Effects of Zn2+ and beta-lactoglobulin concentrations, as well as contact time, on the aggregation of beta-lactoglobulin were examined. All factors exhibited a combined effect on the size of aggregates, whereby larger aggregates were obtained at increased concentrations of Zn2+ and beta-lactoglobulin. At fixed concentrations of 2% (w/v) beta-lactoglobulin and 10 mM Zn2+, the particle size of the aggregates increased from 0.19 microm (at 15 min) to 0.38 microm (at 2880 min). Further, a hyphenated technique of SdFFF and inductively coupled plasma-optical emission spectrometry (ICP-OES) was used to examine whether intermolecular ionic bridges take part in salt-induced beta-lactoglobulin aggregation. With SdFFF-ICP-OES, protein-cation-protein cross-linkages were observed for beta-lactoglobulin aggregation induced by Zn2+, but not for that induced by Ca2+.