| Summary: | This study investigated the effects of zinc fortification (to 100% of the USRDA) and calcium fortificant type (calcium carbonate or calcium phosphate) in various cereal products on zinc, iron and calcium solubility following an in vitro digestion procedure simulating the human process. Due to the dramatic increases in the consumption of high fiber cereal grains and the potential for essential mineral deficiencies, these effects have become increasingly important. In vitro systems included skim, 1 and 2% fat and whole milk because cereal grains are often consumed with such dairy products. In systems containing either highly or moderately fortified whole wheat cereals, zinc solubility significantly increased in response to zinc fortificant level. The superior solubility of calcium carbonate was evident, with associated increases in zinc and iron solubility apparently due to a competitive ion effect. Mineral solubility was significantly enhanced in the presence of milk, with this effect related to % milkfat and the process of homogenization. It was hypothesized that the superior mineral solubilization potential of homogenized whole milk was a function of interfacial protein denaturization during processing. Therefore, experimental dairy processes with the potential to alter native protein morphology (sonication, increased pressure and sequential homogenizations plus added surfactant, and microfluidization) were evaluated. In various cereal systems following the simulated digestion procedure, only a 20 min skim milk sonication treatment significantly enhanced mineral solubility, while surfactant addition inhibited it. Gel exclusion chromatography and photon correlation spectroscopy were used to characterize the effects of the various experimental dairy processes on milk particle hydrodynamic diameter. While surfactant addition prior to whole milk homogenization slightly increased particle diameters, microfluidization decreased them. Isolation and characterization of a milk fraction exhibiting maximal mineral sequesterization potential involved centrifugation, electrophoresis and electron microscopy. Centrifugal separation of zinc fortified whole and skim milk indicated that zinc was associated with a sedimentable fraction. Electrophoretic analysis demonstrated that this fraction was largely composed of sedimented casein and serum albumin. As well, electron microscopic analysis of this fraction confirmed the presence of sedimented casein micelles devoid of lipid globules, an observation supported by quantitative lipid and protein analyses.
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