Evaluating the Ultra-High Pressure Homogenization (UHPH) and Pasteurization effects on the quality and shelf life of donkey milk

Donkey milk has functional properties of great interest to human nutrition. The effects of ultra-high pressure homogenization (UHPH) at 100 MPa, 200 MPa and 300 MPa in comparison with different pasteurization treatments of 70 °C for 1 min and 85 °C for 1 min on the physicochemical quality and shelf-life of treated and raw (untreated) donkey milk were studied. Gross composition and pH, total mesophilic counts, lysozyme activity and physical stability were studied during storage at 4 °C for 28 days. The compositional profile showed resemblance to that of human milk characterized by high lactose, low fat and low protein content and was least affected by the treatments. UHPH treatments at 200 MPa, 300 MPa and 85 °C were able to maintain steady pH during storage whereas the low intensity treatments showed a significant decrease. The observed lysozyme activity in the samples was generally high and appeared to have been enhanced by the applied UHPH and pasteurization treatments with no significant change during storage. Although the raw milk showed good initial microbial quality, extensive growth of mesophilic microorganisms occurred after 7 days of storage, unlike the treated samples which were able to maintain significantly low counts throughout the storage period. The physical stability of milk was negatively influenced by the higher UHPH treatments of 200 MPa and 300 MPa which exhibited sedimentation phenomenon, while creaming was insignificant.