Baseline composition and microbial quality assessment of raw milk from endemic small ruminants and Maghrebi camels in the oasis area of Tunisia

Abstract

Characteristics and quality aspects of milk from native ovine queue fine de l’Ouest (QFO) and the local goat population were investigated and compared with those of the local Maghrebi camel. A total of 378 individual milk samples were collected from lactating animals reared in the continental oasis region of Tunisia. Samples were analyzed for physical parameters (pH, density, and acidity), chemical composition (dry matter, fat, protein, lactose, casein, ash, and casein-protein ratio), mineral concentrations (Ca, P, Na, and K) and microbiological features (total mesophilic aerobic bacteria (TMAB), total coliform count (TCC), lactic acid bacteria (LAB), sulphite-reducing Clostridium (CSR), yeast and molds (Y/M), Staphylococcus aureus (S. aureus), Escherichia coli (E. coli), and Salmonella) according to standard methods. The results obtained for milk characteristics revealed noticeable disparities between the three species. The mean values of pH, density, and acidity in milk collected from sheep appeared higher than those in milk collected from goat species. Compared to the camel populations, sheep species produced milk with similar pH but higher density and acidity. Between camel and goat species, pH and acidity were higher in Negga, while the density was similar. For milk composition, the results showed a remarkable variation among all studied species and an obvious superiority of the ovine species over the caprine and camel populations in all the chemical contents being studied, except for the casein-protein ratio, which is in favor of goat species. The milk of QFO sheep, the richest in casein and protein, was expressed with significantly higher levels of calcium and phosphorus than goat and camel milk. Compared to small ruminants, milk from camels is the richest in Na and K. Additionally, more Ca is present in milk from camels than goats. Goat milk, the poorest type of milk in Ca and Na, contains on average more P than camel milk and more K than sheep's milk. The poor bacteriological quality was that of camel milk for all microbial counts. The microbial quality of goat milk was higher than that of ewe milk based on TMAB, TCC, and E. coli counts, while ovine milk was of better quality, referring to LAB, Y/M, and S. aureus values. No significant differences were found for Staphylococcus aureus and Escherichia coli between the examined species. The obtained results highlighted the complete absence of the two dangerous pathogens Salmonella and CSR in all investigated milk samples. The microbiological examination evidenced that the milk of small ruminant species complies with standard criteria required by Tunisian legislation on the hygiene of milk and dairy products. Regarding camel milk, the microbial analysis revealed poor quality that exceeds standard criteria.