Tunable self-association of partially dephosphorylated beta-casein

Abstract

The utilization of bovine casein for creating casein micelles with properties resembling those in human milk presents an opportunity to bridge the nutritional gap between human milk and infant formula. However, the processing of these innovative structures and ingredients remains uncharted territory. While previous studies have examined temperature-induced self-association of dephosphorylated β-casein (β-CN) by varying single factors, the structuring events of industrially manufactured β-CN ingredients have not yet been fully described. In this study, a calcium depleted β-CN was prepared from micellar casein isolate by cold microfiltration. Partial dephosphorylation was carried out using alkaline phosphatase and quantified though intact protein analysis by LC-MS. In situ self-association was investigated during heating (15–75 °C, 1 °C increments) in a multichannel spectrophotometer, with absorbance and static light scattering (SLS) being monitored. An experimental design was employed to investigate the impact of calcium concentration (0–9 mM), β-CN concentration (2.5–10 mg/mL) and degree of dephosphorylation. The results demonstrate that altering the calcium concentration has a significant impact on tuning of the temperature-induced self-association of β-CN. Notably, at 0 mM calcium, irreversible self-association was not observed, and increasing calcium concentration led to a decrease in the temperature of initial self-association. Partial dephosphorylation also had a significant impact, resulting in an increased temperature at initial self-association. The calcium to β-CN ratio exerted a significant impact on the self-association temperature, while the β-CN concentration alone had no pronounced effect. Furthermore, it was demonstrated that calcium-phosphate bridges were not solely responsible for the self-association protein interactions of partially dephosphorylated β-CN.