Characterization of physicochemical and rheological properties of Gorontalo local goat milk for dairy technology applications

The physicochemical and rheological characteristics of goat milk are critical in determining its processing potential and nutritional value. Although Indonesia possesses a wide variety of goat breeds, comparative scientific data on milk quality among these breeds is limited. This study examined the physicochemical, rheological, structural, and protein characteristics of raw goat milk from four genotypes: Kacang, local goat, Etawa Crossbreed, and Saanen Crossbreed, all reared under traditional farming conditions in Gorontalo, Indonesia. The aim was to identify breed-specific differences that may influence milk’s nutritional quality and processing suitability. A total of 48 raw milk samples were analyzed using standard compositional assays, sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE), densitometry, amino acid profiling, laser confocal microscopy, rotational rheometry, and colloidal stability measurements. These methods provided detailed insights into protein structure, casein micelle behavior, and textural properties. The results revealed that crossbred goats, particularly Saanen and Etawa, produced milk with higher total protein content, elevated concentrations of specific casein fractions (β-casein, α-casein, and κ-casein), greater viscosity, and richer amino acid profiles - especially glutamic acid, proline, and threonine. Conversely, Kacang goats demonstrated higher whey protein content and increased concentrations of sulfur amino acids, specifically cysteine and methionine. Furthermore, all samples exhibited pseudoplastic flow behavior, comparable zeta potentials, and similar particle size distributions, which collectively indicate consistent colloidal stability across groups. These findings demonstrate that goat breed significantly affects milk composition and rheological behavior. Crossbred goats such as Saanen and Etawa appear more suitable for high-protein dairy products such as cheese and yogurt, whereas Kacang goat milk—with its higher whey protein content—may be better suited for infant formulas or functional beverages requiring easier digestibility.