Degree Type

Dissertation

Date of Award

1992

Degree Name

Doctor of Philosophy

Department

Food Science and Human Nutrition

First Advisor

Patricia A. Murphy

Abstract

Soy proteins have excellent functional properties that can be utilized in improving the quality of processed foods. The off-flavor problem in soy proteins caused by short chain aliphatic aldehydes interacting with them makes these products unacceptable to the consumers. Upto date the complete removal of the off-flavor from soy products has not been reached. Complete reversibility of flavor binding to soy proteins was assumed in studying ligand binding to soy proteins, which is contradictory to the fact that removal of the off-flavor from soy proteins is almost not feasible. In order to test the validity of this assumption it was necessary to measure the amount of aldehyde bound to soy proteins directly. This necessitated the use of a radiolabeled aldehyde ligand;[superscript]14C-Heptanal was synthesized by incorporating Na[superscript]14CN into iodohexane by nucleophilic substitution in dimethyl sulfoxide. The resulting heptanitrile was selectively hydrogenated by diisobutyl aluminum hydride in methylene chloride at -80°C to yield [superscript]14C-heptanal. The synthesized radiolabeled aldehyde was used to study the reversibility of aldehyde flavor binding to glycinin and [beta]-conglycinin, by using exhaustive elution on a Sephadex-G-25m gel filtration column. Protein unfolding using urea, together with exhaustive elution was used to examine the involvement of flavor entrapment within the protein as the cause of tight interaction of aldehyde with soy proteins. Sequential blocking of some amino acid residues of the polypeptide chain was carried out to determine the functional groups involved in the tight interaction of aldehydes;The [superscript]14C-heptanal was synthesized in 55% yield, while the purity was 90% and the incorporation of the [superscript]14C-label was 52%. Both soy proteins had high binding capacities for [superscript]14C-heptanal such that saturation was not reached at 1000 ppm [superscript]14C-heptanal. The interaction between [superscript]14C-heptanal and both soy proteins was not completely reversible due to the presence of a significant level of tight interaction. Entrapment of aldehyde and Schiff base formation with the [epsilon]-amino group of lysine were not major contributors to the tight interaction of [superscript]14C-heptanal with soy proteins. Hydrophobic interactions were found to be the sole contributor to tight interaction between the [superscript]14C-heptanal and the soy proteins in an aqueous medium.

DOI

https://doi.org/10.31274/rtd-180813-13050

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Sharma Marini Cooray

Language

en

Proquest ID

AAI9234800

File Format

application/pdf

File Size

93 pages

Share

COinS