Isolation and characterization of cat milk proteins

Miik proteins have important nutritional and physiological roles in the newborn, ranging from providing amino acids for facilitating nutrient uptake and development of the gut. Our knowledge regarding the proteins in cat milk is still very limited. In this study, mature cat milk samples (1 mo of lactation) were collected from domestic shorthair cats. A method was developed for efficient separation of casein and whey proteins by adjustment of the pH to 4.6 followed by ultracentrifugation. Fast Protein Liquid Chromatography (FPLC) using an anion-exchange column (Mono-Q) was used to separate the proteins. Purity of isolated proteins was assessed by polyacrylamide gradient gel electrophoresis. Amino acid composition was analyzed following acid hydrolysis using a Beckman 3600 Analyzer. The major whey proteins with MWs of 14, 19, 20, and 78 kD were isolated to purity. Comparison of their amino acid compositions to known whey proteins from other species suggest that these are lysozyme, β-lactoglobulin A and B, and transferrin.