Physicochemical properties of skim milk powder dispersions after acidification to pH 2.4-3.0 and heating

摘要

Application of skim milk powder (SMP) in acidified beverages is limited due to precipitation and sedimentation of caseins. In this study, 5% w/v SMP dispersion was acidified to pH 2.4-3.0 using citric acid and heated at different conditions. Lowering pH resulted in dissolution of colloidal calcium phosphate from casein micelles, corresponding to lowered turbidity and reduced hydrodynamic diameter of dispersions. When heated for 10 min at different temperatures, 70 degrees C was the most effective to produce transparent dispersions; whereas a shorter heating time between 2 and 60 min was desired at 90 degrees C. The decreased turbidity after heating was attributed to weakened hydrophobic interaction between casein molecules based on fluorescence spectrometry and ion analysis. Scanning transmission electron microscopy showed the altered structure and decreased dimension of casein micelles after acidification and heating. The current study may expand the use of SMP for manufacturing new types of protein drinks.