Effect of stage of lactation on the physical and chemical composition of Drâa goat milk

Abstract

Raw milk characterization constitutes a preliminary and an important step to take account in order to obtain an optimal technological valorization. Among other factors, breed, feed and stage of lactation are the most important factors that influenced cheese making and other dairy products valorization. Thus, this study proposes to analyze the physicochemical composition of Drâa goat milk and to study raw milk fluctuations throughout a complete lactation period. The study was carried out in the Experimental Station of Errachidia (Southern Morocco). In this context, sixteen goats were selected and sampled every week during a period of 160 days (average lactation length). A total of 128 samples of raw goat milk were analyzed according to international standards. Analyses were focused to determination of pH, acidity, density, Dry Matter (DM), Solids Non Fat (SNF), ash, fat and Total Nitrogenous Matter (TNM). Average values were about 17.8°D for acidity, 13.3% for Dry Matter, 0.73% for ash, 4.16% for fat and 3.60% for Total Nitrogenous Matter. In general, theses values are largely situated in the upper level of the range suggested by several Moroccan and foreign researchers for other goat species. On the other hand, the evolution of physical and chemical parameters throughout  lactation stages showed that dry matter, fat content and total nitrogenous matter increased significantly throughout the lactation period; the opposite was found for density (p<0.001). No significant (p>0.05) changes were shown for milk acidity and the average found was around 17°D. Content of milk ash increased significantly during the late lactation stage compared to the earliest and the opposite was observed for pH.The results of the  present investigation show that Drâa goat milk is rich with desirable  components like fat and protein for dairy product manufacturers, and that the late lactation stage seems to be the best period to ensure an optimum technological valorization.

Key words: Goat, Morocco, milk, physicochemical, lactation