Does the addition of donkey milk inhibit the replication of pathogen microorganisms in goat milk at refrigerated condition?

Currently, donkey milk is receiving an increasing attention from consumers and research community because of its several beneficial aspects, such as a poor allergenic nature and a remarkable antimicrobial compound content. In this study, we evaluated the growth rate of Staphylococcus aureus ATCC 6538, Listeria monocytogenes ATCC 7644TM, Campylobacter jejuni ATCC 33291, and Pseudomonas aeruginosa ATCC 27853 at refrigeration conditions (4 +/- 2 A degrees C) in goat milk added with different percentages of donkey milk (1, 2.5, 5, 10% v/v) along 6 days of storage; furthermore, donkey milk and goat milk samples were employed as controls. Lysozyme content of donkey milk was determined and ranged from 1 mg.mL(-1) up to 2 mg.mL(-1). An inhibited growth rate in donkey milk samples was observed during storage for S. aureus, L. monocytogenes, and C. jejuni, with a growth decrease of 0.61 log CFU.mL(-1), 5.55 log CFU.mL(-1), and 1.72 log CFU.mL(-1), respectively. These data confirm the antibacterial activity of donkey milk against Gram-positive and Gram-negative microorganisms; however, microbial growth rates in milk mixtures and goat milk were comparable, with no significant increase in antibacterial activity due to donkey milk addition. Considering a potential employment of donkey milk in dairy products, further studies should be performed in order to detect the optimal balance of milk mixtures in terms of caseins and antimicrobial molecules amounts.