Plant Bioproducts by Guanqun Chen & Randall J. Weselake & Stacy D. Singer

Author:Guanqun Chen & Randall J. Weselake & Stacy D. Singer
Language: eng
Format: epub
ISBN: 9781493986163
Publisher: Springer New York

8.4.4 Bean Protein

Dry beans including navy (Phaseolus vulgaris), pinto (Phaseolus vulgaris), lima (Phaseolus lunatus), kidney (Phaseolus vulgaris), black (Phaseolus vulgaris), white (Phaseolus vulgaris), red (Vigna angularis and Vigna umbellata), pink (Phaseolus vulgaris), lentil (Lens culinaris, also known as Lens esculenta), black eye (Vigna unguiculata), black gram (Vigna mungo), garden pea (Pisum sativum), chickpea (Cicer arietinum), moth bean (Vigna aconitifolia), jack bean (Canavalia ensiformis)and tepary bean (Phaseolus acutifolius) are important food sources in many countries. Common dry bean (Phaseolus spp.) seeds contain 15 to 30% protein, on a dry weight basis (Sathe 2002; Yin et al. 2008). The major classes of proteins in dry beans are water-soluble albumin and mildly alkali-soluble globulins. There are also some minor proteins, such as enzyme inhibitors and lectins. Albumin and globulin account for ~80% of the total storage protein with their molecular masses ranging from 10 to 400 kDa. The quantities and ratios of albumins to globulins depend on the species and variety of the dry bean. Generally, dry beans contain 10–30% albumins and 45–70% globulins (Sathe 2002).

Globulins are further grouped by their solubilities at different ionic strengths and by sedimentation in ultracentrifugation. They are classified into vicilin/phaseolin and legumin with coefficients of sedimentation of 7S and 11S, respectively (Danielsson 1949). Both vicilin and legumin can also be distinguished by their oligomeric organization and polypeptide structures. The 7S vicilin/phaseolin is a glycoprotein of three single peptide chains with molecular mass of 50–75 kDa, while 11S legumin is a hexameric protein linked by disulphide bond(s) between acidic α- and basic β-subunits with molecular mass of ~40 and ~60 kDa, respectively. Six polypeptides are linked together to constitute the legumin molecule with a molecular mass of 320–400 kDa (Lawrence et al. 1990; Sathe 2002). The 7S protein accounts for 50–55% of the total globulin protein content in dry beans on a dry weight basis (Sathe 2002). There is an inverse relationship between 7S and 11S concentrations (e.g. increase in the quantity of 7S causes a proportional decrease in the amount of 11S and vice versa, so the net protein concentrations remain constant) (Ogawa et al. 1989). Dry beans have small amounts of other storage proteins in addition to the globulins, including lectins (a tetrameric glycoprotein of 7S) or phytohaemagglutinin with molecular masses of 27–37 kDa, arcelin (a 2S dimer glycoprotein) with a molecular mass of 35–42 kDa, sulphur-rich protein (a 3S dimer glycoprotein) with a molecular mass of 29–32 kDa and enzyme inhibitor proteins (Sathe 2002).

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