Effect of water activity on the functional, colloidal, physical, and microstructural properties of infant formula powder.

We report on the physicochemical changes of infant formula (IF) powder and its macronutrients (lactose, fat, and proteins) under given storage conditions. Colloidal (particle size distribution, emulsion stability and sedimentation), morphological (scanning electron microscopy), thermal (differential scanning calorimetry), structural (synchrotron X-ray diffraction) as well as surface and chemical (X-ray photoelectron and Fourier transform infrared spectroscopies) data were used to elucidate the main cause-effect relationships for microstructural, functional, and other properties of the IF powder. The wetting behavior of the powder was found to be significantly affected by water activity (a) during storage (a in the range between 0.

Study of oxygen transfer across milk proteins at an air-water interface with scanning electrochemical microscopy.

Scanning electrochemical microscopy (SECM) combined with a Langmuir trough was used for studying oxygen transfer across protein films at an air-water interface. The method allows the comparison of the oxygen permeability of different emulsifiers without any concerns of interference of atmospheric oxygen. Two milk proteins, β-lactoglobulin and β-casein, were compared, and the permeabilities obtained were for β-casein PD ≈ 2.

Synthesis and stability of monolayer-protected Au38 clusters.

A synthesis strategy to obtain monodisperse hexanethiolate-protected Au38 clusters based on their resistance to etching upon exposure to a hyperexcess of thiol is reported. The reduction time in the standard Brust-Schiffrin two-phase synthesis was optimized such that Au38 were the only clusters that were fully passivated by the thiol monolayer which leaves larger particles vulnerable to etching by excess thiol. The isolated Au38 was characterized by mass spectrometry, thermogravimetric analysis, optical spectroscopy, and electrochemical techniques giving Au38(SC6)22 as the molecular formula for the cluster.