**6. Effect of the mixture of sheep and goat's milk on yogurt characteristics**

 The results shown in **Table 3** reveal that the moisture value of goat yogurt is higher than the one observed in sheep yogurt, since the addition of milk powder during yogurt production causes a decrease in available water which consequently generates lower water content in the product [18]. On the other hand, sheep milk has higher solids content, and its addition causes a decrease in the moisture value.

 The composition of the yogurt is identical to the composition of the milk that served as its raw material, although there are some differences arising from the bacterial lactose fermentation and the addition of milk powder usually used to increase milk solids and that consequently generates an increase in protein content [38]. Yogurts with goat milk have lower protein values than those produced using sheep milk. This value decreases as the proportion of goat milk in the product increases. [3, 5, 13] also found out that the protein values for goat milk presented values that are between 2.90 and 3.52% lower than those found for sheep milk whose values range between 5.23 and 6.20%. Evidence also showed that the 9.59% protein content obtained for sheep yogurt was lower than that presented in similar studies carried out by other researchers [39–41]. Those studies presented values of 5.05, 6.34 and 4.55% of protein content for sheep yogurt, respectively.

The highest percentage of fat content in sheep's yogurt can reach 80%. Lower percentages of fat content are observed and could be related with several factors such as the animals' diet, the climate, their breed and their lactation stage. Curiously the goat milk yogurt presents contents of approximately 7% of fat, when the expected values are around 5% [6]. This difference may be explained by the breed of the animals.

 As it was the case with the fat and the protein values, the highest value of dry extract is found in sheep milk yogurt (24.95%), while 21.17% is the value found in goat milk yogurt. These findings are in accordance with the content of the raw material, since the dry extract content found in sheep milk can reach 19.06%, while in goat milk dry extract may be up to 12.73%. Besides, the ash content is indicative of the amount of minerals present. The results found for goat and sheep yogurt are higher than the values reported by other authors [34]. The addition of powdered milk may be the source of these particularly high values. The maximum acidity value was found in sheep milk yogurt (18.9 ml/100 g) and tends to decrease as the quantity of goat milk increases. These acidity values are not in accordance with the Portuguese standard NP-694. This standard requires a maximum acidity of 13 cm3 /100 g, although this value is reported to cow milk yogurt.

**Table 4** shows an increase in the values of mineral contents probably due to the addition of milk powder. The addition of sheep milk caused an increase in phosphorus, calcium and magnesium contents, since this type of milk contains a higher amount of these minerals [5]. These results are in accordance with those obtained by other authors [34].


**Table 3.** 

*Physical-chemical characteristics.* 


*Goat and Sheep Milk as Raw Material for Yogurt DOI: http://dx.doi.org/10.5772/intechopen.85084* 

**Table 4.** 

*Mineral contents.* 
