Peptidi bioattivi da latte d'asina ottenuti tramite l'azione proteolitica di batteri lattici selezionati.

Recently, donkey milk has attracted increasing research interest due to its nutritional and functional properties. In fact, thanks to its peculiar composition, it can be considered a pharma-food/nutraceutical product devoted to particularly sensitive categories of consumers (infants, seniors, allergic subjects). Moreover, in Piedmont donkey breeding allows the preservation of environmental areas. An interesting aspect of this new food concerns the possibility to use it as a source of bioactive peptides. It is possible to decrypt bioactive peptides from donkey milk proteins by bacterial proteolysis. Bioactive peptides are able to exert several biological activities: immunomodulatory, antimicrobial, antioxidant, metal chelating, antihypertensive, antithrombitic, cholesterol- and glycaemia-lowering, cell cycle control and opioid-like. For these reasons, hydrolysis of milk proteins by lactic acid bacteria (LAB) proteolytic system is an attractive approach to generate functional foods enriched in bioactive peptides (given the low cost and the positive nutritional image associated with fermented milk drinks and yogurts). Here, the ability of LAB formerly isolated from food to grow in donkey milk were evaluated. However, since milk is not a sterile product but contains its own autochthonous flora, donkey milk was firstly characterized for its resident bacteria and later pasteurized/sterilized in order to inoculate selected LAB strains possessing good proteolytic properties. The identification of endogenous flora reveal that culturable resident bacteria belong to five species among which Lactococcus lactis. A new method of pasteurization, consisting in a double heat treatment at different conditions, has been developed to guarantee sterility, for exogenous bacteria inoculation, without compromising the food matrix. Five different LAB strains belonging to the culture collection of the laboratory of applied and microbial biochemistry of the DBIOS have been tested for their ability to grow in donkey milk e hydrolyze proteins. Among all, L. rhamnosus 17D10 and L. lactis subsp cremoris 40FEL3 were selected as the best peptide producers and the fast growing. After 24 hours of fermentation, carried out by the two strains separately, peptides were collected and tested for the antimicrobial, antioxidant, ACE-inhibitory and metal-chelating activity. Furthermore, to confirm the peptide enrichment obtained after fermentation (compared to non-fermented milk) a MALDI-TOF analysis was performed. The obtained results indicate that the employment of both and L. rhamnosus 17D10 and L. lactis cremoris 40FEL3 is a valid strategy to decrypt from donkey milk peptides displaying antioxidant and/or antimicrobial activity. The antibacterial efficacy was demonstrated against both Gram negative (E.coli) and Gram positive (S. aureus), strains and this is of great interest due to the widespread antibiotic resistance. Finally, in view of producing a fermented donkey milk (yog-donk), EPS production by the two strains in the donkey milk matrix was evalauted,. Together, the results obtained in this work support the employment of selected LAB to produce high quality fermented products based on donkey milk.