Effect of whole milk concentrate carbonation on functional, physicochemical and structural properties of the resultant spray dried powder during storage

• Carbonation produced powders with reduced surface fat and increased occluded air.
• During storage, fat surface coverage on particles increased due to fat release.
• Improvement of powder's functional properties with CO2 was not observed.

The effect of carbonation (1000 and 2000 ppm) on whole milk concentrate and the resultant spray dried whole milk powder (WMP) was investigated in this research. Carbonation was found to produce WMP with reduced surface fat content, dispersibility, solubility and true density, and increased occluded air content. During accelerated storage at 37 °C for 18 weeks, the surface coverage of fat on powder particles increased from 51, 29 and 8 to 94, 88 and 69% (WMP without treatment and treated with 1000 ppm and 2000 ppm CO2 respectively) due to the release and spreading of encapsulated fat. In addition to the release of fat onto the surface, microscopy observations showed the migration of free fat into the powder particle vacuoles. Meanwhile, dispersibility and solubility of the powders decreased during storage for 18 weeks. These results suggest that carbonation may result in powders with better shelf life due to the reduced surface fat content. Improvements in functional properties was not observed, possibly due to the fine size of the powders (<15 μm) that may have masked the positive effect of carbonation.