An Investigation on the Effect of Ionic Strength and Homogenization Pressure on Rheological Properties, Particle Size Distribution and Separating Serum in HMP Stabilized Doogh

Document Type : Research Paper



Doogh- the popular Iranian drink- is a product of lactic fermentation of milk and its dry matter standardized by dilution of yoghurt (following fermentation) or milk (prior to fermentation). One of the basic problems occurring during its storage is serum separation. Optimum consistency accompanied by no separation of serum during storage are two desirable characteristics looked for. High Methoxyl Pectin (HMP) is proposed to prevent serum separation and modify rheological properties of the fermented dairy drink. Since electrostatic forces play in important role on stabilization of Doogh through with HMP, salt concentration and ionic strength of the medium affect the HMP stabilizing behavior. On the other hand, homogenization affects stability of Doogh by changing its particle size distribution. In this study, 0.25% HMP was added to saline water (0.5 and 1%) with the resulting solution added to yoghurt until the Doogh of 4%dairy solid non fat was produced. The final product was homogenized at either 150 or 250 bar and then their particle size distribution and rheological properties evaluated. The results revealed that salt significantly affected the stabilizing behavior of HMP and particle size distribution characteristic of HMP stabilized the product Doogh.