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Advanced Ohmic Heating for Rice Cooking: Quality Factor Assessment.

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Title:Advanced Ohmic Heating for Rice Cooking: Quality Factor Assessment.
Authors:Liu, Junhuang
Contributors:Food Science (department)
Date Issued:Aug 2018
Publisher:University of Hawaiʻi at Mānoa
Abstract:Conventional thermal processing of foods containing particulates significantly relies on
several heat transfer steps, including conduction and convection, which usually take longer
cooking times for the solid-liquid mixture foods and tend to be overly conservative ensuring
microbial safety, thus compromising quality. Rice is one of the world’s biggest cereal crops next
to wheat and maize and is one of the most important staple foods for the world population. Asian
people consume cooked rice at almost every meal. Existing methods of cooking are about 10-15%
thermally efficient. The ever-increasing population will need more amount of energy and water to
be spent on rice cooking. Advanced food processing technologies such as ohmic heating and
microwave heating have been developed in the last few decades as alternatives to conventional
processing methods. The advanced technologies could contribute to shortening processing times,
energy savings, and high-quality safe food. The microwave heating has been employed to cook
rice and can reduce the cooking time by more than 40% compared to the conventional cooking
method. However, the energy consumption was nearly doubled. Therefore, a new concept to use
ohmic heating for rice cooking has been extensively evaluated. This technology was an attractive
alternative method with high energy transfer efficiency, time savings, and high quality of purpose.
In this study, an alternative cooking method that offers both high energy efficiency and
short cooking time was developed, and a static ohmic heater was designed and fabricated to heat
treat rice-water mixtures. The energy consumption, textural characteristics of rice, and simulation
of the electrical field in ohmic heater were investigated. Two types of rice were used in this study:
white rice and brown rice respectively. The electrical conductivities of rice-water mixtures at
various volume ratios were measured during the rice cooking process. The endpoint of rice cooking
by using ohmic heating was identified. The results showed that the rice cooked by the ohmic
heating method has significantly different textural properties from rice cooked by an electric rice
cooker. The magnitude of texture difference was dependent on the type of rice. The electrical
conductivities of white rice, and the brown rice mixture were approximately 0.03-0.08, 0.04-0.1,
0.06-0.12 S/m at volume ratios of 1:0.8, 1:1.2, 1: 1.5 and 0.025-0.16, 0.032-0.2 S/m at volume
ratios of 1:1.5 and of 1:2 respectively. The research also found that ohmic heating required a
cooking time of around 17-18 min. The estimated amount of energy consumed by the ohmic
heating process was about 1/4 of the total energy consumed by electric rice cooker. The developed
ohmic heating technique showed a great potential over the conventional electric cooker regarding
the high energy efficiency, shorter cooking time, and lower water usage.
Description:M.S. Thesis. University of Hawaiʻi at Mānoa 2018.
URI:http://hdl.handle.net/10125/62437
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections: M.S. - Food Science


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