**3. Goat and sheep milk**

Goat milk has a white-matte colour, does not contain β-carotene and has a sweet and pleasant distinctive "freshly milked taste"; however, it can sometimes, at the end of lactation or after a period of storage in a cold environment, acquire a certain flavour one can describe as "animalic". Sheep milk, on the other hand, shows a more marked white opacity and has a distinctive odour originally called "suarda" or "sheepy". This feature is relatively less evident in milk that is stored in good hygienic condition. The intense flavour of goat milk may be due to the release of short-chain fatty acids during the handling of milk [5], and it has a density that ranges between 1.026 and 1.042 with a pH ranging from 6.3 to 6.7 [15]. It is naturally alkaline, unlike cow's milk which is slightly acidic.

 The major components of any mammalian milk are water, fat, protein, lactose and minerals [16, 17], as shown in **Table 1** for goat, sheep and cow milk. The water content found in goat milk is similar to cow milk and is approximately 87% [18]. Goat milk also has a higher content of nonprotein nitrogenous substances and contains fewer types of casein than sheep and cow milk [6]. This specific characteristic leads to a weaker structure in goat milk yogurt, unlike sheep milk that has good coagulation capacity [6]. Moreover, the differences in sheep milk caseins are the main factors for curd fitness time to be shorter and rennet coagulation time to be firmer [19]. Goat and sheep milk also contains higher amounts of minerals and vitamins than cow milk [6].


### **Table 1.**

*Comparison of the physicochemical characteristics of goat, sheep and cow milk.* 

The micellar structures of sheep and goat milk differ from cow milk in the diameter, hydration and mineralisation. Goat casein micelles contain more calcium and inorganic phosphorus, are less solvated and less stable to heat and lose casein more easily than bovine casein micelles [20]. Lipids appear in the form of smallersized globules in goat and sheep milk, contributing to a better digestibility [3]. An intensive research on sheep and goat milk has revealed that lipid components might have a great deal of benefits. Studies focused on trans-acid and conjugated isomers of linoleic acid, since the latter are believed to have beneficial effects on human health while the former seem to have certain negative effects. As for minerals, the differences between the three types of milks are shown in **Table 2**.

Sheep milk is the type of milk that has the highest amount of calcium, phosphorus and magnesium, while goat milk has higher amounts of potassium, chlorine and manganese. Minerals have great importance in the composition of the milk of any species. The most important minerals in the constitution of milk are calcium, sodium, potassium and magnesium [21]. Thus, milk mineral fraction is characterised mainly by its high calcium content linked to casein phosphoserine, and it is the calcium-protein binding that gives milk its irreplaceable character [17].

Calcium and phosphorus are two fundamental elements of the micelle structure of caseins and will condition the stability of the colloidal phase, particularly calcium which is also very important biologically [22].

