Date of Graduation

8-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Food Science (PhD)

Degree Level

Graduate

Department

Food Science

Advisor/Mentor

Griffiths G. Atungulu

Committee Member

Sammy Sadaka

Second Committee Member

Andy Mauromoustakos

Third Committee Member

Philip G. Crandall

Fourth Committee Member

Rusty Bautista

Keywords

Industrial microwave, rice drying

Abstract

The 915 MHz industrial microwave is a novel technology that has the potential to achieve one-pass drying of rice within a short drying duration and reduce rice drying losses. However, processing recommendations for the commercialization of this technology for rice drying is lacking. The goal of this research is to provide processing conditions that are useful for the commercialization of the 915 MHz industrial microwave technology for rice drying. This was achieved by studying the impact of microwave specific energy and processing conditions such as harvest moisture content, milling duration, and aging on the physicochemical properties of a 915 MHz microwave-dried rice. Two rice cultivars, a medium grain cultivar Titan and long grain hybrid cultivar XL753 with harvest moisture contents of 16%, 18% and 20% (wet basis) were used for the study. The rice samples were treated with two different drying methods, natural air drying as control and microwave heating at 915 MHz frequency (specific energies ranging from 360-720 kJ/kg-grain) followed by tempering and natural air cooling. The rice samples were dehulled and milled for 30 s, 45 s, and 60 s. Physicochemical and functional properties of the head rice samples were analyzed. Furthermore, some head rice samples were stored for 6 months at 4°C and 25°C representing non-aged and aged samples respectively. Physicochemical properties of the aged and non-aged rice samples were determined. Results indicate that microwave specific energy had a significant effect (p-value <0.0001) on moisture removal and head rice yield. The most desirable specific energy for moisture removal that maintains rice quality characteristics (relative to control samples) was 525 kJ/kg-grain. Statistical models predicted harvest moisture content of 20% and milling durations of 45 s and 42 s for processing microwave-dried rice cultivars Titan and XL753 respectively, to obtain rice with good quality characteristics. Furthermore, aging/storage significantly increased the setback viscosity, cooked rice hardness and gumminess, and significantly decreased the peak viscosity and solid loss of microwave-dried rice. Aged microwave dried rice that was treated at 360 and 525 kJ/kg-grain were practically equivalent in terms of hardness and solid loss. Therefore, microwave specific energy of 525 kJ/kg-grain is recommended for rice drying because it produces rice with desirable drying, physicochemical properties and functional properties. This research provides science-based information that is vital for optimizing processing conditions of rice dried using the 915 MHz industrial microwave and for selecting microwave parameters that will achieve desirable physicochemical characteristics required for different rice products.

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