Microbial Populations of Fresh and Cold Stored Donkey Milk by High-Throughput Sequencing Provide Indication for A Correct Management of This High-Value Product

Abstract

Donkey milk is receiving increasing interest due to its attractive nutrient and functional properties (but also cosmetic), which make it a suitable food for sensitive consumers, such as infants with allergies, the immunocompromised, and elderly people. Our study aims to provide further information on the microbial variability of donkey milk under cold storage conditions. Therefore, we analysed by high-throughput sequencing the bacterial communities in unpasteurized donkey milk just milked, and after three days of conservation at 4 °C, respectively. Results showed that fresh donkey milk was characterized by a high incidence of spoilage Gram-negative bacteria mainly belonging to Pseudomonas spp. A composition lower than 5% of lactic acid bacteria was found in fresh milk samples, with Lactococcus spp. being the most abundant. The occurrence of microbial species belonging to risk group 2 was found in fresh milk. After three days of cold storage, the bacterial biodiversity of donkey milk was strongly reduced, since about 93% of the bacterial communities were identified as different species of psychrotrophic Pseudomonas. In conclusion, we report a preliminary description of the microbial diversity of donkey milk by using a metagenomic approach and encouraging a correct exploitation of this high-value niche product.

Investigation of donkey milk bacterial diversity by 16S rDNA high-throughput sequencing on a Cyprus donkey farm

“…The presence of LAB, including Lactobacillus and Streptococcus, was indicated in all donkey milk samples, with average relative abundance of 2.42% (ranging from 1% to 4%). These results are in agreement with the other 16S rRNA gene amplicon-HTS studies of Soto Del Rio et al (2017) and Russo et al (2020) on donkey milk microbiota, in which the average relative abundances of LAB were 4.2% and 2.55%, respectively. The LAB are commonly detected in milk and dairy samples due to their capacity to ferment lactose successfully (Quigley et al, 2013b;Kamilari et al, 2019).…”

“…Still, the identification of the origin of the milk microbiota remains largely unknown. In agreement with other studies on donkey milk microbiome (Soto Del Rio et al, 2017;Russo et al, 2020), the plethora of the detected bacteria are considered environmental. Their existence in donkey milk might come from external contamination of the breast (or udder) during nursing, derived from the mother's skin or the infant's oral cavity.…”

“…Other genera commonly occurred include Acinetobacter, Lactobacillus, Streptococcus, Ralstonia, Clostridium, and Flavobacterium. Previous metage-nomic studies in donkey milk microbiota have also detected the presence of these genera, except Clostridium, but in different relative abundances (Table 5;Soto Del Rio et al, 2017;Russo et al, 2020). Soto Del Rio et al (2017 indicated that the predominant genera were Pseudomonas, Ralstonia, Sphingobacterium, Acinetobacter, Cupriavidus, and Citrobacter, although the core bacterial representation differed among samples.…”

“…Previous HTS studies on donkey milk bacterial communities identified increased relative representation of gram-negative bacteria, such as Pseudomonas spp. (Soto Del Rio et al, 2017;Russo et al, 2020).…”

Presence and persistence of Pseudomonas sp. during Caspian Sea-style spontaneous milk fermentation highlights the importance of safety and regulatory concerns for traditional and ethnic foods

“…The milk used in this study was within the shelf life and stored under conditions ideal. Thus, it is possible to assume that failures occurred during the pasteurization process (Elmoslemany et al, 2010;Vidal et al, 2017;Martin et al, 2018;Russo et al, 2020). Recalls of pasteurized milk contaminated with spoilage bacteria are relatively frequent (Kumaresan & Villi, 2008;Quigley et al, 2013;Samet-Bali et al, 2013;Walsh et al, 2016).…”