Surface energy analysis (SEA) and rheology of powder milk dairy products.

Results of inverse gas chromatography adsorption/desorption experiments using selected probes on skimmed milk, whey and demineralised whey powder materials are presented. The dispersive component of surface energy was found to be dominant, indicating a low polarity character. Surface energy profiles of demineralised whey and skimmed milk showed a characteristic steep exponential decrease from approximately 170 mJ/m(2) to 60 mJ/m(2) and 140 mJ/m(2) to 45 mJ/m(2), respectively, whereas whey powder exhibited a constant (non-exponential) surface energy at approximately 45 mJ/m(2). The dispersive surface energy of demineralised whey and skimmed milk powder showed a broad distribution ranging from 40 mJ/m(2) to 120 mJ/m(2) and 175 mJ/m(2), respectively. In contrast, the dispersive surface energy distribution for whey was very narrow, ranging from only 42.8 mJ/m(2) to 45 mJ/m(2). The determined yield locus and Mohr's circles indicated that demineralised whey exhibited free flowing powder characteristics, whereas skimmed milk and whey exhibited cohesive powder flow behaviour.