Physico-chemical characterization of legumin-T from faba bean (Vicia faba L)

Dry bean protein functionality

Dry beans are an important source of proteins, carbohydrates, dietary fiber, and certain minerals and vitamins in the human food supply. Among dry beans, Phaseolus beans are cultivated and consumed in the greatest quantity on a worldwide basis. Typically, most dry beans contain 15 to 25% protein on a dry weight basis (dwb). Water-soluble albumins and salt-soluble globulins, respectively, account for up to 10 to 30% and 45 to 70% of the total proteins (dwb). Dry bean albumins are typically composed of several different proteins, including lectins and enzyme inhibitors. A single 7S globulin dominates dry bean salt soluble fraction (globulins) and may account for up to 50 to 55% of the total proteins in the dry beans (dwb). Most dry bean proteins are deficient in sulfur amino acids, methionine, and cysteine, and therefore are of lower nutritional quality when compared with the animal proteins. Despite this limitation, dry beans make a significant contribution to the human dietary protein intake. In bean-based foods, dry bean proteins also serve additional functions that may include surface activity, hydration, and hydration-related properties, structure, and certain organoleptic properties. This article is intended to provide an overview of dry bean protein functionality with emphases on nutritional quality and hydration-related properties.

Limited tryptic hydrolysis of pea legumin: molecular mass and conformational stability of legumin-T

The investigation of hydrodynamic and thermodynamic properties and the determination of the molecular mass of legumin-T, the product of limited tryptic hydrolysis of the 11-S-globulin from pea seeds, was carried out to ascertain the structural relationship to globulin-T's from other legumin-like proteins. The obtained legumin-T preparation has a molecular mass M(W)=260+/-10 kDa and M(S,D)=270+/-20 kDa. The secondary structure of legumin-T is characterised by a high percentage of beta-sheet conformation, comparable to that of native legumin and a reduced percentage of helical conformation. The conformational stability of legumin-T evaluated by equilibrium unfolding in the presence of guanidinium chloride was only slightly reduced in comparison to the native legumin, whereas the calorimetrically determined denaturation enthalpy and Gibbs energy of denaturation were found to be increased for legumin-T. These physicochemical properties are very similar to those of faba bean legumin-T.

Structural and functional changes of faba bean legumin during super-limited tryptic hydrolysis

The influence of a super-limited tryptic hydrolysis on physicochemical and surface functional properties of faba bean legumin has been studied using size-exclusion HPLC, SDS-PAGE, UV and fluorescence spectroscopy, fluorescence probe techniques, surface tension measurements as well as determination of emulsifying activity index (EAI) and emulsion droplets diameter (D). The extent of legumin hydrolysis comprised the range between about 14 and 60 split peptide bonds per molecule resulting in a stepwise decrease of legumin molecular weight to 240 kDa (legumin-T) via discrete intermediates with characteristic subunit patterns. These changes are accompanied by an increase in the surface hydrophobicity and the exposure of aromatic chromophores. No differences were found in the surface tension between the variously hydrolyzed legumin samples. Best emulsifying properties (highest EAI and lowest D values) were attained after a rather low tryptic hydrolysis (about 30 split peptide bonds per mol). Further hydrolysis impaired the emulsifying parameter which were, however, higher (EAI) or lower (D) than those for native legumin.