Extraction, fractionation and characterization of bitter melon seed proteins.

Protein fractions (water-soluble/albumin, salt-soluble/globulin, alkali-soluble/glutelin, and alcohol-soluble/prolamin) were extracted from defatted ripe bitter melon seed (Momordica charantia) using water, 1 M sodium chloride solution, alkali/pH 11.0, and 70% ethanol, sequentially. The main protein fraction was albumin (49.3%), followed by globulin (29.3%) and glutelin (3.1%). No prolamin was detected, and 18.3% of the protein was nonextractable. The surface hydrophobicities of albumin, globulin, and glutelin were 757, 1,034, and 292, respectively. The molecular sizes of all the fractions were mostly about 45 and 55 kDa. The denaturation temperatures of albumin, globulin, and glutelin were 111.9, 117.3, and 133.6 degrees C, respectively. The levels of all essential amino acids in the bitter melon protein fractions met the minimum requirements for preschool children (FAO/WHO/UNU) with the exception of Thr. Bitter melon protein fractions with unique protein profiles and higher denaturation temperatures could impart novel characteristics when used as food ingredients.