Date of Graduation

5-2017

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

Seo, Han-Seok

Second Committee Member

Wang, Ya-Jane

Third Committee Member

Sadaka, Sammy S.

Keywords

Biological sciences; Applied sciences; Decontamination; Drying; Grain; Microwave; Processing; Rice

Abstract

An industrial microwave (MW) system operating at 915 MHz frequency was used to dry high moisture content (MC) (23% to 24% wet basis) medium-grain rough rice samples (cv. Jupiter). The rice beds were contained in a modified tray that accommodated up to 9 kg of rice separated by thin fiberglass mesh in 3 kg increments. Each layer of rice was fitted with fiber optic sensors connected to a real time data logger during MW treatments. It was determined that drying rice to a MC of 14% to 16% was feasible with the application of MW specific energy at 600 kJ/kg-grain followed by 4 hours of tempering at 60°C. Resulting head rice yield (HRY) was not significantly different from that of control samples dried gently using natural air. Increasing MW specific energy resulted in an increase in rice surface lipid content (SLC), rice protein content, final and peak viscosities. Total color differences (TCD) decreased with increasing MW specific energies. Increasing MW specific energy resulted in decreases in rice microbial loads. At the highest specific energy of 900 kJ/kg-grain, the reduction of the aerobic bacterial and aflatoxigenic fungal loads was 4.56 and 2.93 log CFU/g-grain, respectively. Varying rice bed thickness had significant effects (p < 0.05) on rice final surface temperature, HRY, milled rice yield (MRY) and aerobic bacteria count. Highest MRY and HRY were observed at the top and middle layer with bottom layer having the smallest. Similar trends were observed for the aerobic bacteria response. Optimization analyses suggest that a power of 10.00 kW and a heating duration of 6.00 min are preferred for optimum aerobic bacteria and A. flavus mold count, MRY, HRY and FMC of rice beds of equivalent bed thickness of 15 cm. These factor levels equate to a specific energy of 400.00 kJ/kg-grain. At these parameter settings, a ton of freshly harvested rice the energy required to dry a ton of freshly harvested rough rice was 111.11 kWh. Drying at this MW specific energy for batch processes will cost $9.88 per ton of rice.

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