Position of acetyl groups on anhydroglucose unit in acetylated starches with intermediate degrees of substitution

Jianteng Xu; Yong-Cheng Shi

doi:10.1016/j.carbpol.2019.05.059

Position of acetyl groups on anhydroglucose unit in acetylated starches with intermediate degrees of substitution

Carbohydr Polym. 2019 Sep 15:220:118-125. doi: 10.1016/j.carbpol.2019.05.059. Epub 2019 May 21.

Authors

Jianteng Xu¹, Yong-Cheng Shi²

Affiliations

¹ Department of Grain Science and Industry, Kansas State University, Manhattan, KS 66506, USA.
² Department of Grain Science and Industry, Kansas State University, Manhattan, KS 66506, USA. Electronic address: ycshi@ksu.edu.

PMID: 31196529
DOI: 10.1016/j.carbpol.2019.05.059

Abstract

Waxy, normal, and high-amylose maize starches were acetylated to various degrees of substitution (DS) in aqueous medium. A stepwise addition of acetic anhydride enhanced reaction efficiency and DS was in the order of high-amylose maize starch (DS 1.72) > waxy maize starch (DS 1.60) > normal maize starch (DS 1.03) when 240% (w/w) acetic anhydride was added. Starch acetates were further fully esterified to DS 3.0 using acetic anhydride-d₆ or propionic anhydride to analyze position of acetyl groups on anhydroglucose unit (AGU) by ¹H NMR. Regioselective 2-O-acetyl starches were produced when the DS was lower than 0.14. At DS 1, the distribution of acetyl groups was ca. 44%, 32%, and 24% at C-2, C-3, and C-6 positions, respectively, regardless of amylose content. Deuterated acetyl group was a preferred secondary substituent over propionyl group in subsequent ¹H NMR analysis because it resulted a clean spectrum without interference from propionyl methyl protons.

Keywords: (1)H NMR; Peracetylation; Starch acetate; Substituent distribution.