Shelf life of donkey milk subjected to different treatment and storage conditions

Abstract

The aim of this study was to investigate the effects of different treatment conditions on microbiological indicators of donkey milk hygiene and their evolution during shelf life at 4 and 12°C from 3 to 30d, simulating a farm-scale pasteurization and packing system. Four treatment conditions were tested: no treatment (raw milk), pasteurization (65°C × 30 min), high-pressure processing (HPP), and pasteurization plus HPP. The microbiological quality of the raw donkey milk investigated was not optimal; our results highlight the importance of raw milk management with the need for animal hygiene management and good dairy farming practices on donkey farms to improve handling procedures. The raw milk treated with HPP alone showed visible alterations with flocks, making the milk unfit for sale. The microbiological risk posed by consumption of raw donkey milk was significantly reduced by heat treatment but farm-scale packing systems cannot guarantee an extended shelf life. In contrast, the pasteurization plus HPP treatment was the most effective method to maintain microbiological milk quality. Microflora growth had little effect on pH in donkey milk: pH values were significantly different only between raw milk and pasteurized and pasteurized plus HPP milk stored at 12°C for 3d. Alkaline phosphatase activity and furosine could be used as indicators of proper pasteurization and thermal processing in donkey milk. Moreover, the presence and growth of Bacillus cereus in the case of thermal abuse hamper the wide-scale marketing of donkey milk due to the potential consequences for sensitive consumers and therefore further tests with time/temperature/high-pressure protocols associated with B. cereus are needed. Finally, our study shows that an HPP treatment of pasteurized milk after packing extends the shelf life of donkey milk and assures its microbial criteria up to 30d if properly stored at 4°C until opening; therefore, combined heat treatment and storage strategies are recommended to enhance the shelf life of donkey milk.

Characterization of bacterial communities of donkey milk by high-throughput sequencing

“…Furthermore, previous studies, using culture-dependent methods, had found that Pseudomonas spp. is an important component of the DM microbiota (Cavallarin et al, 2015;Giacometti et al, 2016). This observation is consistent with a previous report that indicated Pseudomonas spp.…”

“…Pasteurized donkey milk is usually sold directly from the farms. However, considering its target consumers and nutritional properties, it can be sold raw, with 3 days of shelf life (similar to raw bovine milk) (Giacometti et al, 2016).…”

Management Practices and Milk Production in Dairy Donkey Farms Distributed Over the Italian Territory

“…It is recognised that only few Regions adopt a specific legislation for producing and selling donkey milk (5,22,23). Furthermore, little information is available on the best solutions for donkey milk processing (24,25,26) and more studies are needed to clarify how these procedures modify milk properties in terms of nutritional value, food safety, and organoleptic characteristics.…”

Equine Milk Production and Valorization of Marginal Areas—A Review

“…In Europe, the dairy equine enterprise started up in France as part of a project on animal diversity preservation [21], and spread out in many marginal areas of the world where these monogastric herbivores are well adapted to difficult environments, with scarce availability of forages, often of poor-quality. Today, equine milk is mainly marketed for human consumption as raw, pasteurized, or freeze-dried [22], and as fermented derivatives [15]. In Italy, the price of donkey milk ranges from 9 to 15 €/L of raw milk, 14 to 17.5 €/L of pasteurized milk, and 27.5 to 36 €/100 g of powdered milk, either spray dried or lyophilized [23,24].…”