30C-14 |
Biochemical characterization of Val bean (Dolichos lablab L.) proteins |
M. VENKATACHALAM, H. H. Kshirsagar, R. Tiwari, and S. K. Sathe. Department of Nutrition, Food and Exercise Sciences, Florida State University, 402 Sandels Bldg., College of Human Sciences, Tallahassee, FL 32306-1493 Val bean is an underexploited tropical legume that is valued for its nutritional and sensory attributes. It is also known by several other names such as butter bean, helmet bean, Egyptian kidney bean, lubia bean, and hyacinth bean; to name a few. Although agronomic and nutritional characteristics of Val bean have been investigated, Val proteins remain largely unexplored. Val bean seeds were ground to approximately 40-mesh flour and defatted using petroleum ether. Seed protein content was determined by micro-Kjeldahl procedure (N X 6.25). Albumin, globulin, prolamin, and glutelin fractions were prepared from defatted flour. Polyacrylamide gel electrophoresis was used to study protein polypeptide composition. Protein fractions were stained by Periodic acid-Schiff staining to detect presence of glycoproteins. Amino acid composition of proteins was determined by Waters Pico-Tag column amino acid analyzer. Protein in vitro digestibility was assessed at 370C using pepsin (protein to pepsin ratio of 100:1 w/w) and 50 mM HCl as the digestion buffer. On a dry weight basis, Val contained 30% protein. Albumin, globulin, prolamin and glutelin respectively accounted for approximately 20, 48, 1 and 31% of the total seed proteins. Val globulin is a glycoprotein composed of at least three polypeptides in the molecular weight range 51-64 kDa. Sulfur amino acids were the first limiting amino acid in total seed proteins. Both native and heat denatured albumin and glutelin fractions were easily hydrolyzed by pepsin in < 1 min at 370C. Native globulin was resistant to pepsin however heat denatured globulin (1000C, 30 min, boiling water bath) was rapidly digested, in < 1 min, by pepsin at 370C.
Session 30C, Food Chemistry: Proteins
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