Abstract: The microrheological characteristics and stability of set yogurt made from camel and cow milks during fermentation were analyzed by multi-frequency diffusion wave spectroscopy and multi-light scattering spectroscopy, respectively, and their titratable acidity, viable bacterial count, viscosity, water-holding capacity and texture indexes were determined. The results showed that it took 9.5 h for camel milk and 6.5 h for cow milk to reach the end point of fermentation. The results of microrheological analysis showed that as a fluid with low viscoelasticity, fermented camel milk had lower elasticity index (EI) and macroscopic viscosity index (MVI) but higher flow factor (FF) and solid-liquid balance (SLB) values than fermented cow milk. The results of multiple light scattering spectroscopy showed that fermented cow milk was more stable than fermented camel milk during fermentation, while the opposite was true during storage, indicating that the internal structure of fermented camel milk, with higher stability, was more compact. During storage, the titratable acidity of fermented camel milk was lower than that of fermented cow milk, and the numbers of viable bacteria in both of them were more than 1 × 107 CFU/mL, a significant difference being observed between them (P < 0.05), and the water-holding capacity of fermented camel milk was higher than that of fermented cow milk. Texture analysis showed that the hardness, consistency and viscosity index of fermented cow milk were all significantly higher than those of fermented camel milk (P < 0.05). In summary, it is not easy for camel milk to form a gel structure after fermentation, but because of the tight internal structure, fermented camel milk is stable, which is more favorable for product storage. In contrast, it is easier for cow milk to form a thick and dense texture after fermentation. This study provides a theoretical basis for the practical application and promotion of fermented camel milk, and provides ideas for the diversified development of fermented non-bovine milks.

Key words: fermented camel milk; fermented cow milk; microrheology; multiple light scattering