Starch granule architecture, water sorption, and interactions with surfactants
Abstract
Properties based on the granular structure of starch from various plant sources were investigated. Granular structures were observed using confocal microscopy and an array of fluorescent and reflective probes of various sizes. Results showed that probes up to 0.2 μm in diameter may be capable of penetrating the granule matrix, in contrast to the commonly accepted exclusion limit for starch (1000 da). Use of fluorescent microspheres demonstrated that channels in corn starch exist under pristine native conditions at all developmental stages and, thus, are not artifacts produced from drying or solvent treatment. Methods for determining water sorption of granular starch were investigated with the ultimate goal of monitoring water sorbed during chemical derivitization under high salt/pH conditions. Blue dextran exclusion (including alternative polymer-dyes) and NMR relaxometry techniques were investigated. Key problem areas of the blue dextran method were identified as the adsorption of aromatic ring-containing functional groups (dye), which is aggravated by the presence of lyotropic salts, and the insolubility of leached amylose and its incompatibility with dextran and other water-soluble polymers. It was found that heating mixtures was a requirement for significant losses of blue dextran to occur. Using relaxometry, water contents of maize (Zea mays L.) starch could be accurately determined only in the absence of bulk water. The granular structure of several maize genotypes was investigated by examining interactions with surfactants during gelatinization and the resultant amylose-surfactant complexes. The amount of complexation, determined from DSC endotherms upon reheating the sample, was directly proportional to amylose content. Subtraction of gelatinization endotherms obtained with and without surfactant present produced an exotherm which occurs Concomitantly with the gelatinization endotherm. The exotherm is proposed to be the formation of starch-surfactant complexes. It was also demonstrated that ionic surfactants, i.e. both anionic and cationic, were granule destabilizing at a hydrocarbon tail-length of 12. Neutral surfactants, or those with longer tail-lengths, did not exhibit the effect.
Degree
Ph.D.
Advisors
BeMiller, Purdue University.
Subject Area
Food science
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