Christiane Mercier

Determination of Starch with Glucoamylase

Publisher Summary This chapter focuses on the determination of starch with glucoamylase. Isolation and purification of the enzyme, glucoamylase, have led to the development of a more specific method for starch determination. The use of glucoamylase allows the quantitative transformation of starch into d -glucose, which can be determined specifically with glucose oxidase. The method is applicable to starch determination in complex media, including all starchy products—food and feed, digestive contains—and glycogen. The results obtained are neither affected by the presence of polysaccharides formed from residues other than d -glucose nor from d -glucose residues bound by linkages. By using a total hexose in conjunction with this method, it is possible to determine the total amount of normal and modified starch products present in a sample.

Molecular structure of unmodified and chemically modified manioc starches

Unmodified (1) and a modified (2, O-2-hydroxypropyl distarch phosphate) manioc starch were hydrolyzed with pullulanase, beta-amylase, and/or amyloglucosidase and the hydrolyzates fractionated on Sephadex G-50. The amylopectin of 1 had one chain of d.p. 45 to 7.5 chains of d.p. 15. Debranching of2 with pullulanase yielded only one half of the d.p. 15 chains obtained from 1. The further beta-amylolysis of the debranched 2 was incomplete, although all of the debranched d.p. 15 chains were converted into maltose and maltotriose. Beta-amylolysis of 1 and 2 was 61 and 34%, respectively, and hydrolysis by amyloglucosidase was 93 and 49%, respectively. The relative amounts of the chromatographed fractions suggest that about one-half of the d.p. 15 chains of 2 contained no modifying groups. A model depicting the possible sites of 2-hydroxypropyl and/or phosphate groups on the modified manioc amylopectin molecule is presented.

Gelatinization and melting of maize and pea starches with normal and high-amylose genotypes

Abstract Normal and high-amylose maize and pea starches (gene ae and ra respectively) were studied during gelatinization by their swelling and solubility patterns, as well as by differential scanning calorimetry. High-amylose (> 60%) starches showed restricted swelling and solubility, compared to normal maize (25%) and pea (35%) genotypes. At low water volume fractions (ν 1

Macromolecular structure of wrinkled- and smooth-pea starch components☆

Abstract Starches from wrinkled and smooth pea (Pisum sativum L.) have been fractionated quantitatively, using successive thymol or 1-butanol complexation and differential ultracentrifugation. The fine structures of their components were determined by using sequential treatment with isoamylase and/or beta-amylase, followed by gel-permeation chromatography. Amylose (70.9%) and amylopectin (7.8%) of wrinkled-pea starch are similar structurally to their smooth-pea equivalents (33.2% and 64.7%, respectively). The average molecular weights were higher for the smooth-pea components (amylose: M n 170,000, M v 697,000; amylopectin: M w 80.6 × 106) than for the wrinkled-pea components (amylose: M n 125,000, M v 430,000; amylopectin: M w 19.4 × 106). An intermediate fraction (18.9%) of low molecular weight ( M n 25,100), isolated only from wrinkled-pea starch, was composed of the same short (S, d.p. 15) and long (L, d.p. 45) linear chains as amylopectin, but the ratio S/L was 3.6 in contrast to 9.6 for wrinkled-pea and 8.1 for smooth-pea amylopectins.

Interactions of concanavalin A with α-d-glucans

Abstract The interaction of α- d -glucans with Concanavalin A has been studied by turbidimetry. Amylopectins from various botanical sources and two glycogens were characterised for their fine structure [% (1→6)-α-linkages, % beta-amylolysis, iodine interaction] and their molecular size (intrinsic viscosity, gel permeation). Branched α- d -glucans with defined structures were prepared either by enzymic (beta-amylolysis or phosphorolysis of oyster glycogen and amylopectins) or mild acid hydrolysis of waxy-maize amylopectin. Selection of high concentrations of Con A (>0.9 mg/mL) and (20m m , Tris-HCl) buffer allow high sensitivity for studying the interactions. Two structural features of branched polysaccharides are demonstrated to be major parameters for the interaction, namely, the hydrodynamic volume and the external chain-length. At pH 7.0, the Con A interaction modifies the beta-amylolysis kinetics by decreasing the affinity constant of beta-amylase, whereas no modification was detected at pH 5.2.