Masters Theses

Sze-chin Chen

Date of Award

8-1969

Degree Type

Thesis

Degree Name

Master of Science

Major

Food Science and Technology

Major Professor

Melvin R. Johnston

Committee Members

Jimmie L. Collins, J. A. Corrick Jr

Abstract

The objective of this study was to determine the effect of hot water followed by microwave energy and microwave energy followed by boiling water on the heating, inactivation rate of peroxidase and the firmness of small whole potatoes. In experiment one, lots of potatoes receiving the hot water followed by microwave energy treatments were held first in hot water for 1, 3, and 5 min. periods. At each of these periods samples of potatoes were subjected to microwave energy for 0, 1, 2, 3, 4, and 5 min. This design which permitted 18 treatments was replicated 3 times. Under the conditions of this experiment the following results were found: 1. The minimum period of time for treatment found to completely inactivate peroxidase were as follows: 1 min. hot water followed by 4 min. microwave energy, and 3 min. hot water followed by 3,1 min. microwave energy and 5 min. hot water followed by 2,15 min. microwave energy. 2. The heat gradient was from the periphery to the core. 3. Temperature for inactivation of peroxidase at 1,5 cm. depth was higher than at 0.75 cm. This was due to the longer heating period required at the depth of 1,5 cm. 4. Firmness of potatoes at the point when peroxidase was just inactivated were: 95 lb., 1 min. hot water followed by 4 min. microwave energy; 150 lb., 3 min. hot water followed by 3.1 min. microwave energy; and 160 lb., 5 min. hot water followed by 2.15 min. microwave energy. In experiment two, treatments consisted of heating samples for 0.5, 1.0, 1.5, and 2 min. by microwaves. Samples from each of the microwave treatments were heated subsequently in boiling water for periods of 0, 1, 2, 3, 4, and 5 min. This design which permitted 24 treatments was replicated 3 times. Under the conditions of this experiment the following results were obtained: 1. When the potatoes were heated by microwaves a heat gradient developed from the core toward the periphery. 2. Because of the heat gradient of the potatoes, the temperature at a 1.5 cm. depth was higher than that at 0.75 cm. This heating phenomenon was different from the finding of experiment one. 3. Due to the heat patterns produced by microwaves followed by boiling water, there were two zones of enzyme inactivation prior to complete inactivation. These zones of inactivation occurred initially at the core and periphery. 4. The minimum treatment time found to completely Inactivate peroxidase and the firmness values after these treatments were as follows: 119 lb., 1.5 min. microwave energy followed by 3 min. boiling water and 124 lb,, 2 min. microwave energy followed by 2 min. boiling water. 5. When the procedure of experiment one was followed, a longer period of time was required to inactivate peroxidase in the whole potato than when the procedure of experiment two was utilized. However, the firmness of tubers from experiment one was higher than the firmness of potatoes from experiment two.

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