Hydration Of Milk Power And Its Effect On Texture Of Yogurt

Due to the demand of yogurt has been increased gradually, in the case of highcost of raw milk and the production shortfalls, so milk powder has been chosen foryogurt by dairy companies. Milk protein can be denatured and properties of milkpowder can be changed by high-temperature treatment. Reconstituted milk andfermented yogurt have a significant impact on the quality of milk powder. In thisexperiment,27kinds of milk powder from different regions and batches werecollected, and basic ingredients of milk powders were analyzed to screen thedifferences in milk samples. Then the impact of rehydration of milk powder underdifferent pH, temperature, NaCl and CaCl2concentration to yogurt texture wasstudied.The basic ingredients of27kinds of milk powders and the viscosity and particlesize of reconstituted milk(11%) were determinated to choose15kinds of sample withdifferences. The heat-aggregated molecular weight and particle morphology of milkpowder were studied to divided15kind of milk powder into4categories: highvariability?denatured, low variability and skim milk powder.The impact of different pH(6.0~7.0, interval0.2), temperature(25~85?,interval15?), NaCl concentration(0.01~0.10mol/L, interval0.2mol/L),CaCl2concentration(0.01~0.10mol/L, Interval0.2mol/L) to rehydration of milk powderwere analyzed. The wetting time, settling time, degree of dispersion, solubility ofmilk powder and the particle size, turbidity and surface hydrophobicity ofreconstituted milk were used to index the milk powder rehydration conditions. Theoptimal powder rehydration conditions were the average solubility of whole milkpowder could be increased to11.56%when pH were6.8,26.77%when at thetemperature was55?,10.31%when NaCl concentration was0.02mol/L,10.68%when CaCl2concentration was0.04mol/L. Four kinds of milk powder(TLM3?QC?HY2?TZ) hydrated by four kinds ofrehydration conditions was hydrated under different hydration time(0.5~4h?interval1h) and the reconstituted milk was used to ferment yogurt. The impact of hydrationtime and other factors to the texture of yogurt were analyzed. Four kinds ofrehydration conditions were: A:6.8of pH,55?,0.04mol/L of NaCl concentration;B:6.8of pH,55?,0.02mol/L of CaCl2concentration; C:6.8of pH,55?of distilledwater and D? non-treated distilled water. The results showed that the TPAcharacteristics of reconstituted milk yogurt A and B were better than those of C andD. As the increase of the hydration time, the hardness viscosity, consistency andcohesion of yoghurt were enhanced. During the3~4h of hydration time, TPAcharacteristics were practically stable. The analysis of sensory evaluation showed thetexture and flavor of reconstituted milk yogurt produced by low denatured milkpowder under hydration condition A were the best.Based on the results above, a theoretical basis for the production of reconstitutedmilk fermented yogurt can be provided by this paper.