Alkali-assisted extraction of proteins from meat and bone residues of harp seal (Phoca groenlandica)

Proteins from mechanically separated seal meat (MSSM) or bone residues thereof were extracted at pH 10.5 over a 1-h period at 20 °C and subsequently precipitated at pH 4.5–5.5. Washing of the resultant precipitate with acetone removed a large portion of haem pigments and effectively improved the colour of the product. The recovery of proteins from MSSM ranged from 56.92 to 63.88% and that for bone residues was 12.02–13.07%, depending on the extraction temperature employed. Precipitates obtained at pH 4.5 contained 85.88% moisture, 12.43% proteins, 0.31% minerals and 1.08% lipids. The moisture content of the acetone-washed product was decreased to 8–15% with a lipid content of 1.10%, on a dry-weight basis. Protein efficiency ratio (PER) values for extracted proteins from MSSM (3.13) and seal bones (3.09) were higher than those for beef (2.8) and pork (2.5) and similar to that for cod (3.1). Tryptophan was the limiting amino acid in the protein isolates. Among the free amino acids, taurine was present at 22.9 mg%. This amino acid is important for functional regulation of the eyes, heart, muscles and central nervous system. Alkali-extracted proteins of seal meat had excellent fat adsorption, emulsifying capacity and emulsion stability. The nitrogen solubility index (NSI) value of the products was similar to those obtained for base-extracted proteins from chicken bone residues.