Date of Graduation

12-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Food Science (PhD)

Degree Level

Graduate

Department

Food Science

Advisor/Mentor

Ya-Jane Wang

Committee Member

Andronikos Mauromoustakos

Second Committee Member

Griffiths Atungulu

Third Committee Member

Scott Osborn

Fourth Committee Member

Suresh Thallapuranam

Keywords

Arabinoxylans, Bran yield, Breaking force, Head rice yield, Porosity, Rice bran thickness

Abstract

Rice is typically consumed as whole kernel, which makes the economic value of whole kernels twice that of brokens. Macro-structural defects such as fissures and chalkiness have been recognized to weaken kernel mechanical strength, and thereby increase breakage during milling. However, high percentages of brokens are sometimes recorded even though these defects are controlled prior to milling. It was hypothesized that rice milling characteristics are influenced by endosperm porosity from the structural arrangement of chemical components and by bran thickness and composition. Thus, this study aimed to modify chemical components by applying treatments to alter rice porosity and its associated physicochemical properties, and to investigate the factors that influence bran removal during milling. Brown rice kernels were subjected to protein denaturation (PD) via heat treatment and/or lipid removal (LR) via hexane extraction and then characterized for porosity, breaking force, swelling power, water solubility, gelatinization, and pasting properties. The bran thickness of brown rice kernels was measured, and then milled to varying times. Bran fractions were then collected, quantified, and analyzed for their chemical compositions. The results showed that although porosity was generally negatively correlated with kernel hardness, porosity was influenced by the quantity of proteins and lipids, whereas kernel hardness was primarily affected by protein composition. Gelatinization temperatures were increased by PD but decreased by LR. Both PD and LR resulted in reduced pasting viscosities and swelling properties. Milling characteristics were not significantly impacted by bran thickness, but rather by the chemical components of arabinoxylans and proteins. The results demonstrate the impacts of rice physical and chemical properties on rice milling characteristics. Results gained will assist rice breeders to develop cultivars with desired chemical compositions and help rice processors optimize processing conditions to improve rice milling quality.

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