Composition and Molecular Weight Distribution of Carob Germ Protein Fractions

Abstract

Biochemical properties of carob germ proteins were analyzed using a combination of selective extraction, reversed-phase high-performance liquid chromatography (RP-HPLC), size exclusion chromatography (SEC) coupled with multiangle laser light scattering (SEC-MALS), and electrophoretic analysis. Using a modified Osborne extraction procedure, carob germ flour proteins were found to contain approximately 32% albumin and globulin and approximately 68% glutelin with no prolamins detected. The albumin and globulin fraction was found to contain low amounts of disulfide-bonded polymers with relatively low M(w) ranging up to 5 x 10(6) Da. The glutelin fraction, however, was found to contain large amounts of high molecular weight disulfide-bonded polymers with M(w) up to 8 x 10(7) Da. When extracted under nonreducing conditions and divided into soluble and insoluble proteins as typically done for wheat gluten, carob germ proteins were found to be almost entirely ( approximately 95%) in the soluble fraction with only ( approximately 5%) in the insoluble fraction. As in wheat, SEC-MALS analysis showed that the insoluble proteins had a greater M(w) than the soluble proteins and ranged up to 8 x 10(7) Da. The lower M(w) distribution of the polymeric proteins of carob germ flour may account for differences in functionality between wheat and carob germ flour.