**2. Materials and methods**

 To support this work, a well-documented research on goat and ewe milks and on their suitability for yogurt making was conducted. The main sources of information were scientific papers and books. A research previously carried out by the authors and that included information about the milk obtained through mechanical milking of Serrana Jarmelista goats and Serra da Estrela sheep in the centre region of Portugal was also considered. Milk was pasteurised at 65°C during 30 minutes and then it was cooled to 4°C.

Yogurt was produced using goat and sheep milk in accordance with experimental group obeying to the following proportions of sheep and goat milk: 100% of sheep milk (O100C0), 80% of sheep milk and 20% of goat milk (O80C20), 50% of sheep milk and 50% of goat milk (O50C50), 40% of sheep milk and 60% of goat milk (O40C60), 20% of sheep milk and 80% of goat milk (O20C80) and 100% of goat milk (O0C100). The lactic bacteria used in the yogurt production were lyophilized *Streptococcus thermophilus* and *Lactobacillus delbrueckii* ssp. *bulgaricus*. Commercial cow milk powder (12%) was added to all the yogurts that were produced.

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

 The yogurt samples were placed in hermetically sealed bottles for fermentation for 12 hours at 45°C. Then, they were refrigerated at 5°C. The total nitrogen content was measured by the micro-Kjeldahl method [10]. Protein was calculated as N × 5.38. The fat content was determined by the Geber's method [11]. Ash content was determined by incinerating the samples for 24 hours at 550°C. Moisture content was determined by drying samples overnight at 105°C [10]. Total solids content was determined using the gravimetric method as the samples were dried in an oven at 105°C for 24 hours [10]. Phosphorus was determined by spectrophotometric UV/ VIS, 720 nm [12], and calcium, magnesium, potassium and sodium were estimated using flame atomic spectrophotometry at 750 nm [13]. The determination of fatty acids was done using a gas-chromatographic method (GLC), total titratable acidity was determined by reference method [10] and the pH using the potentiometric method.

For the sensorial analysis of samples, an acceptance test with untrained panellists was used. The panel consisted of 25 tasters who analysed the samples of goat and ewe yogurt. A commercial yogurt produced with cow milk and bought at a local market was analysed as well. The grades awarded by each panellist ranged from 1 to 9, where 1 is "extremely unpleasant" and 9 is "extremely pleasant" for attributes such as sweetness, colour, aroma, flavour, texture and overall assessment. To assess the tasters' overall preference, a last question was asked: "Which sample did you prefer?"

 Statistical analysis was performed using the Statistica 12 programme [14] where mean, standard deviation and mode, median, minimum and maximum values were determined.

 The findings were analysed using one-way analysis of variance. Means were compared at a 5% level of significance using LSD test to check significant difference. The Kruskal-Wallis test was used to verify the panellists' preferences regarding the different yogurt samples.
