Suspensions of Calcium Phosphate : Interactions of milk proteins to hydroxyapatite

Sammanfattning: Capolac is a product containing hydroxyapatite (HA) from Arla Food Ingredients, to be used for calcium fortification. The adsorption of casein and whey proteins onto the Capolac was investigated, aiming to solve the sedimentation problem of this insoluble calcium phosphate. The adsorption of casein from sodium caseinate (SC) and whey protein from whey protein isolate (WPI) was first analyzed with pure HA particles. Different particle size of HA was explored. Zeta-potential measurements and the suspension behavior observations showed that both casein and whey protein adsorbed onto HA particles. The smaller the particle size, the better the suspension stability. Then the adsorption of SC and WPI onto Capolac was explored. Results of zeta-potential measurements, SDS-PAGE, surface protein coverage calculation and turbidity measurements suggested both SC and WPI bound to Capolac and improved the suspension stability. Data analysis was performed to compare the protein adsorption to HA and Capolac, results showed that there was no significant difference between the two particles, means the casein and whey protein adsorb onto both HA and Capolac particles. The higher absolute value of zeta-potential for pure Capolac than pure HA, and the turbidity measurement of pure Capolac indicate a better suspension stability for pure Capolac than pure HA particles. Possible reasons behind this are discussed, in relation to the produce process of Capolac. The adsorption of SC and WPI on to both particles could be fitted in a simple Langmuir model, demonstrating a single layer adsorption of both proteins to the surface of the HA and Capolac particles. Findings from this study proved that both SC and WPI-coated Capolac particles improved the suspension stability. However, the adsorption is a complicated process, the stability and application of the coated particles requires further investigation.