Date of Graduation

12-2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Food Science (PhD)

Degree Level

Graduate

Department

Food Science

Advisor/Mentor

Siebenmorgen, Terry J.

Committee Member

Atungulu, Griffiths G.

Second Committee Member

Osborn, G. Scott

Third Committee Member

Mauromoustakos, Andronikos T.

Fourth Committee Member

Saxena, Ashok

Keywords

Fissuring; Grain inverters; Head rice yield; Rice drying; Rice quality; X-ray imaging

Abstract

Rice kernels with internal fractures of the endosperm, fissures, tend to break during milling, leading to head rice yield (HRY) reductions. Minimizing kernel fissuring is thus an important goal of the rice industry. To minimize fissuring during the drying process, a better understanding of the fissuring process and the kinetics thereof is required. The goal of this research was to use X-ray imaging and glass transition principles to better understand rough rice kernel fissuring. First, because the instance when the fissuring process is initiated and completed during the drying process is not well known, an X-ray imaging setup that allows for in-situ rough rice drying was used to elucidate rough rice fissuring kinetics. For harsh drying air conditions, fissuring occurred and appear instantaneously whereas, for mild conditions, a time delay was required before fissures appeared. Second, a hypothesis known as the glass transition hypothesis has been used to explain fissure formation during the drying process. However, the hypothesis has not been validated from a fundamental fissuring standpoint. With the availability of an X-ray system for fissure visualization in rough rice kernels during the drying process, the glass transition hypothesis was evaluated. Results showed that the glass transition principles proposed to explain fissure formation are valid for various drying air temperatures, rice moisture contents (MCs), and drying air equilibrium MCs associated with rough rice. Third, tempering rice immediately after drying has been shown to minimize fissure formation. However, the effect of tempering on minimizing fissure formation has not been quantified. This study showed that drying followed by tempering can reduce kernel fissuring by up to 50% and increased the percentage points (pp) of MC reduction that can be safely achieved in a single drying pass by 1-2 pp. Finally, grain inverters have been used in commercial cross-flow dryers to improve MC uniformity across the grain column. However, the effect of grain inversion on fissuring and HRY reduction is not known and was therefore evaluated. Results showed that grain inverters in a cross-flow dryer can significantly minimize fissuring and HRY reduction at plenum air temperatures between 55°C and 60°C.

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