Date of Graduation

12-2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Food Science (PhD)

Degree Level

Graduate

Department

Food Science

Advisor

Terry J. Siebenmorgen

Committee Member

Ya-Jane Wang

Second Committee Member

Ruben O. Morawicki

Third Committee Member

Han-Seok Seo

Fourth Committee Member

Andronikos Mauromoustakos

Fifth Committee Member

Scott Osborn

Keywords

Drying, End-use, Functional properties, Gel texture, Rice, Tempering

Abstract

Heated-air drying followed by tempering (HAT) is effective for increasing rough-rice drying rates without compromising head rice yield (HRY). However, heat exposure could affect rice end-use properties. Hypothesizing that the total amount of heat exposure incurred by rice during heated-air drying determines the trend and magnitude of changes in end-use properties, this dissertation sought to 1) characterize the effects of drying and tempering regimen on changes in end-use properties, 2) derive an index to quantify and compare the amount of heat exposure that rice kernels incur during active drying and, 3) relate values of this index to changes in rice end-use properties. A series of drying experiments were conducted on a long-grain rice cultivar. Paste viscosities and texture of rice gels prepared from flour obtained from dried (12.5% MC) rice samples were evaluated. A theoretical framework was developed and employed alongside time-temperature data collected from drying experiments to derive an index for quantifying thermal exposure, Graham-Acquaah’s Thermal Exposure (GATE) value, during drying. Paste viscosities and gel texture were not only dependent on drying air temperature but also on how long the rice was exposed to a given temperature during drying and tempering. Air relative humidity (rh) had an indirect effect on end-use properties. Using different HAT regimens, peak viscosity was altered by 16%, breakdown by 24%, and setback by >500% compared to control samples. Gel strength was increased by approximately 40% with HAT regimens. The GATE values had strong and significant (p

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