To better understand the fermentation kinetic of Arabian donkey milk, its physicochemical properties, conductivity and viscosity were assessed during acidification, and compared to that of the bovine milk. Donkey milk showed a shorter latency phase and slightly lower acidification rate than bovine milk. Measurement of electric conductivity during acidification showed that maximum demineralisation of casein micelles occurred at around pHI 5.44 for donkey milk and pHI 5.16 for bovine milk. Donkey milk was also found to be less viscous. The technological characteristics of donkey milk were different from those of bovine milk due to intrinsic physicochemical properties of both milks.

Non-standard heat treatments, i.e. 68°C 2.5 min -1 , 75°C 10 min -1 and 100°C 5 min -1 , were applied to evaluate the effects on physicochemical and microbiological characteristics of donkey milk compared to bovine milk. The most significant (P<0.05) changes were the decrease of pH, the increase of casein nitrogen and the denaturation degree of whey proteins, which exceeded 80% in donkey milk compared to about 66% in bovine milk, at 100°C 5 min -1 . Conversely, calcium and phosphorus were more heat stable in donkey milk than in bovine milk. Hydroxymethylfurfural (HMF) resulted absent in donkey milk. Significant changes in free fatty acids (FFA) were observed in both heated milks, although donkey milk showed lower lipolysis rates. The lysozyme activity of donkey milk was inversely related to the intensity of heat treatments but even at 100°C 5 min -1 a relevant activity was still observed.