Suspensions of Calcium Phosphate : Interactions of milk proteins to hydroxyapatite

anglais. 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.

anglais. Hydroxyapatite (HA), a major component of human bones and teeth, is an insoluble calcium salt. If it is used for calcium fortification in the food industry, will milk proteins interact with this particle and solve the sedimentation problem? Have you ever met the recommended calcium intake in your body? Perhaps you are one of those who consume insufficient calcium, which, may lead to health risks like osteoporosis. Arla Food Ingredients has developed a product Capolac containing hydroxyapatite to be used in calcium-fortified foods. However, this insoluble calcium salt may encounter problems like sedimentation, off-flavors, etc. when applied in calcium-fortified products. With the increasing demand for “clean label” from consumers, traditional methods to solve this problem like adding stabilizers, or chelating agents is off the table. Besides, the added stabilizers could cause problems to the products like poor texture, bitter or chalky mouthfeel, and so on. This master's degree project is aiming to develop an innovative way to improve the suspension stability of this product, Capolac, which contains 70% of this insoluble calcium salt – hydroxyapatite. According to previous research, milk proteins – casein and whey proteins could adsorb onto the pure hydroxyapatite particles. This project first verified whether the two milk proteins adsorbed on the pure HA particles, then the product Capolac was tested and compared the results with pure HA particles. The source of the two proteins is sodium caseinate (SC) and whey protein isolate (WPI). A variety of methods were implemented to verify and examine the protein adsorption from mainly two aspects: how much the protein bound to the particles and how the suspension behavior appears when mixed with the two different proteins SC and WPI with the two particles HA and Capolac, respectively. Data analysis and modeling were also performed to further prove the correlation and the adsorption pattern. The laboratory results demonstrated that both SC and WPI bond to the HA and Capolac, in other words, SC and WPI-coated HA and Capolac enhanced the suspension stability when suspended in water, as expected. Another finding in this project is that pure Capolac has a better suspension ability than pure HA, which may be due to the Capolac being already partly coated with some protein fractions. This is another proof that protein-coated particles could improve suspension stability. It has been a challenge to choose from organic or inorganic calcium salts to be applied in the calcium fortification products. Each category has its advantages and drawbacks. The findings in this study are a very promising beginning to the development of calcium-fortified products with insoluble calcium salts, like Capolac. The sedimentation problem is likely to be solved, also the bioavailability of the inorganic calcium salts would be expected higher, which requires further investigation.