Fractionation of Regular Corn Starch: A Comparison of Aqueous Leaching

Starch is an extraordinarily versatile polymer used in a wide array of products from paper to prepared foods. Despite its current wide usage, its potential for additional applications continues to be explored. Unfortunately, new creative developments are hampered, in part, because of a lack of detailed structure and function studies on all but the basic amylose and amylopectin molecules. To better understand the relationship between starch molecular structure and its functional attributes, pure fractions of amylose and amylopectin with unique molecular weights (MW) or branching patterns would be desirable. Detailed structure and function data would not only partially aid in the development of new uses for starch but would also assist plant breeders and biotechnologists to develop specialty grains with specific molecular structures. For years, separation and classification of starch into respective amylopectin and amylose components has proven difficult. The most troublesome limitations have been the coexistence of amylopectin and amylose within the starch granule, the existence of an intermediate MW fraction (Whistler and Doane 1961), and the fragile nature of the larger amylopectin molecule. Because granule solvation is a prerequisite for further polymer isolation procedures, these limitations make it practically impossible to yield a sol from which one starch polymer can be precipitated without being contaminated by the other. Most successful fractionation methods cited in the literature have involved aqueous (aq) dispersion (Adkins and Greenwood 1969) or aq leaching (Kerr and Severson 1943, Meyer et al 1949, Banks et al 1959) of granules, and selective retrogradation (Schoch 1945) or alcohol precipitation (Schoch 1945, Whistler and Doane 1961) of one polymer from a starch dispersion. Studies detailing the sequential combination of these general methods, however, are less numerous. In addition, Lansky et al (1949) noted that the lack of standards or methods by which starch fractions could be measured for purity and extent of degradation has hindered progress. Not until recently has high-performance size-exclusion chromatography (HPSEC) begun to play a pivotal role in the classification of starches based on MW distribution (Takagi and Hizukuri 1984, Kobayashi et al 1985, Jackson et al 1988, Jackson et al 1992). HPSEC can also be an important tool in the assessment of starch fraction purity. The objective of this study was to compare the effectiveness of different fractionation procedures in obtaining amylose and amylopectin from regular corn starch.