Rheology and Microstructure of Labneh (Concentrated Yogurt)

Labneh was produced by concentrating milk to approximately 23% total solids (wt/vol) by the traditional cloth bag method (control), ultrafiltration, reverse osmosis, or direct reconstitution. For ultrafiltration and reverse osmosis, membrane processing was carried out either before or immediately after fermentation. Dynamic rheological studies revealed that the physical behavior of labneh was heavily dependent on the protein concentration and the severity of mechanical agitation during membrane treatment. Scanning electron microscopy showed that the higher protein content samples had more compact structure and smaller voids than their lower protein content counterparts. Also, reverse osmosis and ultrafiltration of warm fermented milk had clearly detrimental effects on gel structure, producing thicker casein strands than in the traditional sample. No major differences were observed in the other test samples except gel densities, which varied with the different casein concentrations. In general, ultrafiltration of warm, fermented milk is a promising treatment for the manufacture of good quality labneh.