Abstract
The protein composition of goat milk differs between goat breeds and could present regional trends. The aim of this study was to comparatively analyze the protein composition of goat milk produced by the Alpine and Saanen breeds in northeastern Brazil and to evaluate the antibacterial activity of its protein fractions. SDS-PAGE, 2-DE electrophoresis and RP-HPLC analyses revealed the absence of αs1-casein in the milk of both breeds and no differences between the αs2-casein, β-casein, β-lactoglobulin and α-lactalbumin profiles. The amounts of soluble proteins and β-casein hydrolysis residues were higher in Saanen milk. Only the protein fraction containing the largest amounts of casein (F60–90%) inhibited bacterial growth, with MIC values between 50 and 100 mg/mL. This study describe for the first time three important points about the goat milk protein of two Brazilian goat breeders: absence of α-s1 casein in the protein profile, differences between the milk protein composition produced by goats of Alpine and Saanen breeders and antibacterial activity of unbroken proteins (casein-rich fraction) present in these milk.
Highlights
Milk is characterized as a food matrix of simple access and is abundant in nutrients, such as carbohydrates, proteins, minerals, and vitamins [1]
It has been found that proteins present in the milk and whey of caprine and bovine breeds are precursors of bioactive components, by contributing to particular antimicrobial activities against a broad spectra of pathogenic and spoiling bacteria [17], [18], [19]. Considering these aspects, the aim of this study was to comparatively analyze the protein composition of milk produced by Alpine and Saanen goats in northeastern Brazil and to evaluate the antimicrobial activity of their protein fractions against some strains of pathogenic bacteria
The SDS-PAGE analysis of the crude protein extract (CPE), casein concentrate and fractions of Alpine and Saanen goat milk precipitated with ammonium sulfate revealed no band indicative of as1-cn (Figures 1 and 2)
Summary
Milk is characterized as a food matrix of simple access and is abundant in nutrients, such as carbohydrates, proteins, minerals, and vitamins [1]. The crude composition of the protein fraction of milk from different species of mammals has been characterized, and among them, goat milk stands out due to the presence of compounds with important metabolic properties for human nutrition [3]. The protein fractions of bovine and goat milk are qualitatively very similar, and the major difference among these milks is related to the proportions and classes of caseins [4]. Studies based on molecular techniques have suggested that goat alleles present in different breeds result in significant differences in milk casein fraction, and these alleles can exhibit regional trends for these characteristics [6], [7]
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