Walnuts (Juglans regia L): proximate composition, protein solubility, protein amino acid composition and protein in vitro digestibility

Walnuts contained 16.66% protein and 66.90% lipids on a dry weight basis. N on-protein nitrogen values ranged from 6.24 to 8.45% of the total nitrogen when the trichloroacetic acid concentration was varied within the range 0.2 5-1.0 M. Albumin, globulin, prolamin and glutelin respectively accounted fo r 6.81, 17.57, 5.33 and 70.11% of the total walnut proteins. Walnut protein s were minimally soluble at pH 4.0. The majority of total walnut protein po lypeptides had estimated molecular weights in the range 12 000-67 000. The Stokes radius of the major protein in walnuts (glutelin fraction) was 66.44 +/-1.39 Angstrom. Lysine was the first Limiting essential amino acid in tot al walnut proteins as well as in the globulin and glutelin fractions. Leuci ne and methionine plus cysteine were the second limiting essential amino ac ids respectively for the prolamin and albumin fractions. Hydrophobic and ac idic amino acids dominated the amino acid composition in all protein fracti ons. Native and heat-denatured walnut glutelins were easily hydrolysed by t rypsin, chymotrypsin and pepsin in vitro. (C) 2000 Society of Chemical Indu stry.