Date of Graduation

8-2023

Document Type

Thesis

Degree Name

Master of Science in Food Science (MS)

Degree Level

Graduate

Department

Food Science

Advisor/Mentor

Atungulu, Griffiths G.

Committee Member

Ubeyitogullari, Ali

Second Committee Member

Bautista, Rusty

Keywords

Contemporary rice cultivars; Glass transition temperature; Material state diagram; Nitrogen; Rice

Abstract

Rice is typically harvested at high moisture content (MC) levels which necessitates drying to low MC levels for safe storage. However, drying at inappropriate temperatures and durations can lead to deterioration of kernel quality such as fissure formation. Kernels with these fissures are typically associated with reduced head rice yields and significant economic losses. Material state diagrams for rice have been created by the University of Arkansas Rice Processing Program (UARPP) as a tool to aid in predicting the ideal temperatures to use during drying and tempering (a process of holding rice at the drying temperature for some duration). The diagram is made up of the glass transition temperature (Tg) of rice at various MC levels. The Tg is used to define the boundary of the rice material’s glassy and rubbery states and hence having accurate data on the Tg of rice is imperative to ensuring proper drying and tempering operations. Presently, the current rice material state diagrams were developed for old rice cultivars which may be inadequate for controlling the drying and tempering of the contemporary rice cultivars. Additionally, soil nitrogen application is stipulated to increase rice’s amylose content, which tends to increase the Tg of rice starches. Therefore, the objective of this study was to generate material state diagrams for contemporary rice cultivars as well as determine the impact of soil Nitrogen on the Tg of a contemporary rice cultivar. The study involved conditioning samples of 23 rice cultivars harvested in 2022 to MC levels ranging from 20% to 12% as well as treating a long-grain pure-line cultivar (Diamond) with 6 different nitrogen rates (0, 100, 134, 168, 201, and 235 kg/ha) at the pre-flood stage. A differential scanning calorimeter was used to determine the Tg of these rice samples. The study revealed the average Tg of the rice samples to be 39, 41, 43, 45, and 47°C at MC levels of 20, 18, 16, 14, and 12%, respectively. Rice material state diagrams with these updated Tg were then developed. At a harvest MC of 20%, the brown rice in this study exhibited a slightly higher Tg of approximately 39 ℃ compared to that of previous studies (approximately 36 ℃), along with a better model accuracy of R² = 0.72. The study also revealed that the application of soil nitrogen at 100 and 168 kg/ha caused the Tg of the rice samples to significantly increase. Using this newly generated information, contemporary rice cultivars can be better controlled during drying and tempering.

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