Small ruminants milk from Tunisian oasis: physicochemical characteristics, mineral contents, and microbiological quality

Abstract

Characteristics and quality aspects of milk from native ovine Queue Fine de l'Ouest (QFO) and the exotic D'man (DMN) breeds were investigated and compared with those of two subgroups of the local goat population Arbi and Serti. A total of 418 individual milk samples were collected from multiparous 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, K, and Ca/P) and microbiological features (total mesophilic aerobic bacteria (TMAB), total coliforms count (TCC), lactic acid bacteria (LAB), sulphitereducing Clostridium (CSR), yeast and molds (Y/M), Staphylococcus aureus (S. aureus), Escherichia coli (E. coli), and Salmonella) according to standard methods. The values obtained for physicochemical, mineral, and microbial parameters revealed noticeable differences in the milk of the four studied breeds. On the whole milk samples, the mean value of pH, density, and acidity in milk collected from sheep breeds appeared higher than in milk collected from goat subgroups. As for milk composition, results showed a remarkable disparity between studied breeds and clear superiority of sheep breeds compared to goat's subgroups in all chemical contents being studied (dry matter, fat, protein, lactose, casein, and ash). The differences are more important, especially for dry matter, fat, protein, and casein content, whereas casein/protein ratio distinguished goat's genotypes, and the highest one was obtained for Serti Subgroup. When comparing sheep versus goat's milk for macro-minerals, the current study indicated lower K and higher concentrations of Ca, P, and Na. The milk of QFO sheep, the richest in casein and protein, was expressed with significantly higher levels of calcium and phosphorus compared to the DMN sheep breed and the two goat subgroups. The microbiological examination evidenced that the milk of both species complies with standard criteria required by the Tunisian legislation on the hygiene of milk and dairy products. The microbial quality of ewe milk was higher than goat milk, based on LAB and Y/M, while goats produced milk with better quality referring to TMAB and TCC counts. No significant differences were found for Staphylococcus aureus and Escherichia coli between examined breeds. Got results highlighted the complete absence of the two dangerous pathogens Salmonella and CSR in all investigated samples of small ruminants' milk.