Date of Graduation

12-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Food Science (PhD)

Degree Level

Graduate

Department

Food Science

Advisor/Mentor

Terry Siebenmorgen

Committee Member

Jean Meullenet

Second Committee Member

Andy Mauromoustakos

Third Committee Member

Scott Osborn

Fourth Committee Member

Griffiths Atungulu

Keywords

Airflow Rate, Cross-flow Drying, Glass Transition, Head Rice Yield, Paddy, Rough Rice

Abstract

After harvest, rough rice is dried, then dehulled and typically milled before consumption. A broad objective of the “rice drying process”, which comprises drying and tempering, is to maximize the yield of “whole, intact milled kernels”, quantified by the “head rice yield” (HRY). Since rough rice is commonly dried using cross-flow (CF) dryers in the United States of America, the aim of this research was to assess the effect of drying and tempering treatments on milling yields when rice was dried in an experimentally-simulated CF drying column. First, because airflow rate was found to be the least-studied “drying variable”, its effect on drying air conditions and rice moisture content profiles was assessed. Additionally, the impact of airflow rate on the material state behavior of rice kernels was considered as a means to explain head rice yield reductions (HRYRs). Second, the effect of tempering approach following CF drying on milling yields was investigated. For the same rice and drying conditions, tempering approach significantly affected HRYs, especially HRYs of samples that were located near the heated-air plenum during CF drying. Third, drying treatments were selected based on the glass transition temperature of rice kernels and applied in the drying column. When kernels did not undergo material state transitions during drying, there was negligible HRYR, regardless if samples had been tempered or not. But, when kernels underwent material state transitions during drying, significant HRYRs occurred, and HRYRs of tempered samples were significantly less than those of non-tempered samples.

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