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Enzyme Susceptibility of High-Amylose Starch Precipitated from Sodium Hydroxide Dispersions

¹2200 East Eldorado Street, Decatur, IL 62522.²331 Food Science Building, Dep. Food Science, University Park, PA 16802.³Corresponding author. Phone: 814-863-0481. Fax: 814-863-6132. E-mail address: dbt1@psu.edu

Type III resistant starch (RS) is understood to be due to the ordered structure formation in the process of retrogradation. Most treatments of granular high-amylose maize starch (HAMS) do not completely eliminate the original ordered structure. We hypothesized that residual ordered structure would constrain subsequent physical reassociation of chains and the formation of RS. The objective was to generate differences in enzyme susceptibility using two means of precipitation of fully dispersed starch and to relate differences in enzyme susceptibility to the structure of the precipitates. Dispersions in sodium hydroxide were precipitated either with ethanol or ammonium sulfate. RS and the timecourse of digestion were determined. Crystallinity and helicity were estimated using wide-angle X-ray diffraction and solid-state ¹³C CP/MAS NMR, respectively. Precipitation of whole starch with ethanol led to lower RS values (≈24%) than precipitation with ammonium sulfate (≈39%) and also to higher reaction rate constants for an early component of digestion. Ethanol precipitation of a branched starch fraction gave essentially no RS, whereas ammonium sulfate precipitation of the same branched material had >20% RS. Ethanol precipitates contained single helices, in most but not all cases, contributing to V-type crystallinity. Ammonium sulfate precipitates had double helices contributing to B-type crystallinity.