Isolation and characterization of coconut protein

Abstract

Coconut proteins were fractionated from fully mature coconuts ( Cocos nucifera) by (I) centrifugal means and by (II) cryofractionation and the proteins characterized by analytical ultracentrifugation and horizontal SDS electrophoresis. Method I resulted in four fractions with a recovery of protein of better than 90%. Method II produced a cryosoluble and a cryoinsoluble fraction and a recovery of 68% of the total protein. Amino acid analysis revealed a high content of arginine and glutamic acid in the coconut protein and its centrifugal fractions. Fractions obtained by cryoseparation contained substantially less arginine. Unseparated protein showed three sedimentation peaks of 1.4S; 7.9S and 13.4S, corresponding roughly to the 2S; 7S and 11S peaks in soy protein. There was no evidence for the presence of a 15S peak in this preparation, but a layer of highly polymerized material (gel) was observed at the bottom of the cell. A sedimenting peak of 17.4S was observed in the cryoinsoluble fraction from cryofractionation. The protein in the whole coconut (unseparated fraction) showed three electrophoretic bands with a relative concentration of 31.8% (MW = 16 300), 32.8% (MW = 24 300), and 35.4% (MW = 51 700). The electrophoretic patterns associated with the sediments of cream and skimmed milk fractions from method I were distinct from one another. The skimmed milk protein (7S) contained only one major electrophoretic band with MW of 48 300 daltons. The protein in the sediment from the cream fraction (7.1S and 12.1S) contained two major electrophoretic bands of a relative concentration of 42.2% (MW = 23 200) and 57.8% (MW = 30 300). The cryoinsoluble fraction (6.5S, 11.3S and 17.4S) from method II was electrophoretically heterogeneous with molecular weights ranging from 26 600 to 47 200 while the cryosoluble protein (6.7S) exhibited only a single band with MW of 22 200. The study shows that coconut protein is grouped into roughly the same fractions as soy protein by sedimentation analysis.