The characterization of starches and maltodextrins by proton nuclear magnetic resonance spectroscopy

Krueger, William James

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https://hdl.handle.net/2142/20990 Copy

Description

Title

The characterization of starches and maltodextrins by proton nuclear magnetic resonance spectroscopy

Author(s)

Krueger, William James

Issue Date

1995

Doctoral Committee Chair(s)

Artz, William E.

Department of Study

Food Science and Human Nutrition

Discipline

Food Science and Human Nutrition

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Chemistry, Analytical
• Chemistry, Biochemistry

Language

eng

Abstract

• A new method to quantify the degree of branching in $\alpha$-glucans using proton nuclear magnetic resonance (NMR) has been developed. Instrument parameters and sample conditions were investigated for their effect on determining the $\alpha$-(1,4)/$\alpha$-(1,6) linkage ratios of starches. Two methods were developed using 0.6 N potassium hydroxide-d/deuterium oxide (KOD) (Method I) and dimethyl sulfoxide-d$\sb6$ (DMSO-d$\sb6$) (Method II) as the solvents. A 90 degree pulse width for the (1,4) and (1,6) protons and minimal recycle time were used to eliminate interference from the monodeuterated water (HOD) signal in Method I. The HOD signal was not a problem in Method II. Potassium hydroxide was added to deuterium oxide (D$\sb2$O) to enhance the solubility of amylose in physical mixtures of waxy maize amylopectin and isolated normal corn amylose. Phasing of spectra, drift correction, width of narrowed spectra, and integral size are factors that were found to influence ratio determinations.
• These newly developed methods were used to determine the degree of branching in waxy maize, corn, rice, tapioca, wheat, potato, pea, and high amylose maize starches. The ratios generally increased with increasing amylose content. Amylose content of the starches was determined using the (1,4)/(1,6) ratios of the starches and ratios of several amylopectins assigned as standards. The amylopectin standards were categorized as amylopectin I, II, and III based on their (1,4)/(1,6) ratios of 19, 21, and 30 respectively. Wheat, pea, tapioca, and rice were categorized as containing amylopectin I, maize and potato as amylopectin II, and the high amylose starches most likely belonging to the lightly branched amylopectin III. Results were obtained in less than 30 minutes by this method and were comparable to those obtained by the iodine affinity method, which requires one to two days.
• Attempts were made to correlate various physical properties to (1,4)/(1,6) ratios. Viscosity profiles of starches obtained by a Rapid Visco-Analyzer were found to be dependent on the source of starch. X-ray patterns and granular sizes of the starches were identified. No definite correlations were revealed between these physical properties and the (1,4)/(1,6) ratios.
• An additional proton NMR method was developed to determine the average degree of polymerization, molecular weight, and dextrose equivalent of maltodextrins. This method employed DMSO-d$\sb6$ as an alternative to the more common solvent D$\sb2$O. A small portion of D$\sb2$O or trifluoroacetic acid was used to remove the interference of the hydroxyl signals. The results were comparable to those determined by high performance liquid chromatography. Attempts to utilize this same method for higher molecular weight starches failed due to lack of instrument sensitivity.

Type of Resource

text

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Copyright and License Information

Copyright 1995 Krueger, William James

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