Chemical Composition and Proteomics of Camel Milk at Different Lactation Stages

In this study, the basic nutritional components and physicochemical indicators of camel milk were measured during the early, middle, late, and dry lactation stages to explore their variation patterns throughout the entire lactation process. Meanwhile, quantitative proteomics was employed to analyze the differential proteins between camel colostrum and mature milk and their potential functional information was uncovered. The results showed that the contents of basic nutrients (protein, fat, lactose, and total solids) in camel milk was the highest at the early lactation stage, and subsequently decreased as lactation proceeded. The physicochemical properties of camel milk varied with lactation period. Milk density and refractive index were the highest at the early lactation stage, and then significantly decreased (P < 0.05). The pH and titratable acidity of camel milk were the highest (6.89 and 20.71 °T, respectively) at the dry lactation period. However, lactation period had little effect on the electrical conductivity of camel milk. High-abundance protective proteins such as immunoglobulins, insulin-like proteins, and lactoferrins were found in camel milk, and a total of 641 significantly differential proteins were identified between camel colostrum and mature milk (P < 0.05). In addition, the high-abundance proteins in camel colostrum were mostly related to immune response, anti-inflammatory effect, tissue protection and repair, and metabolic processes, indicating that camel colostrum was more helpful in establishing the immune system against microbial infections in camel calves. This study provides a deep insight into the physicochemical properties of proteins in camel milk during lactation, thereby providing valuable information for the development of functional foods.