Preheating conditions (low-, medium-, and high heat-) did not significantly affect the buffering capacity (BC) of skim milk powder (SMP), whereas the level of demineralization significantly affected the BC of whey powders (WP). Heat treatment (85°C for 30 min) of both SMP and WP (90% demineralized) mixtures (88:12, 76:24, 64:36 and 52:48; SMP:WP) resulted in a reduced BC, and the extent of this reduction increased with the proportion of WP increased in the samples. High-buffering milk prepared by the addition of phosphate salts (40 mM NaH2PO4 and 60 mM Na2HPO4) delayed the rate of pH decline during yoghurt fermentation. The high-buffering yoghurt showed a significantly higher water holding capacity (WHC) than that of control yoghurt (p<0.05), as well as a more uniform and interconnected microstructure with small pore sizes than those of control yoghurt. No significant differences were found between high-buffering and control yoghurt regarding the viable bacterial counts of starter. The manipulation BC can potentially improve the quality characteristics of yoghurts, such as WHC and texture.
Keywords: buffering capacity; quality characteristics; skim milk powder; whey powder; yoghurt.