Seasonal variations in goat milk composition: a comprehensive review

Among the numerous factors influencing goat milk composition, seasonality has a major impact, reflecting changes in lactation stage, diet, and weather. This review aims to synthesize studies comparing the nutrient content of goat milk in summer and winter. Studies reporting on lipids, fatty acids, phospholipids, cholesterol, proteins, urea, lactose, oligosaccharides, minerals and vitamins were included. Data on physicochemical and organoleptic properties were as well reviewed. Various breeds and countries were considered, with particular focus on the Alpine breed. Despite heterogeneity between studies, consistent trends emerged. Compared to winter milk, summer goat milk contained lower concentrations of lipids, proteins and total solids but higher levels of lactose. Summer milk fat showed higher levels of saturated fatty acids and lower levels of unsaturated fatty acids, possibly driven by changes in monounsaturated fatty acids. Summer milk had lower linoleic/alpha-linolenic acid ratios and trans fatty acid levels. Casein content was lower in summer. Summer milk contained lower concentrations of Ca, P, Mg, Na, and Mn, but higher levels of K and Cl than winter milk. Summer milk may be richer in vitamins A, B1, B2 and oligosaccharides. pH and titratable acidity may be lower in summer, whereas the freezing point tended to be higher. After homogenization and heat treatment, summer milk showed lower viscosity, serum-protein denaturation, and serum-protein–casein interactions. Summer milk tended to have a milder flavor than winter milk.