Date of Award

1984

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Abstract

A study of high temperature drying and tempering of parboiled rice was undertaken to evaluate the effects on grain quality. Thirtysix treatments, with three levels of air temperature, three levels of moisture (of rice after exposure in the dryer), and four levels of tempering, were performed on Saturn variety, medium grain rice, parboiled under fixed conditions. The dried and tempered rice samples were then moisture equilibrated under room conditions and subjected to standard milling procedures. Analyses were performed to evaluate color, texture, protein, and strength characteristics of the milled rice. A time-based study of kernel hardness and strength properties was also performed for 93 hours after drying, on separate samples for a selected treatment combination. The intermediate air temperature of 93.3(DEGREES)C, for any single tempering treatment, produced the highest head yield in the rice samples. This trend was sustained over all the moisture levels to which the samples were dried. This trend, together with the increase of color and strength properties of the rice kernels was attributed to the extended parboiling effect at this temperature. The tempering treatment 2, realized the highest head rice yield especially at the 93.3(DEGREES)C air temperature drying treatment. Tempering treatments, in general, other than treatment 1, were beneficial in terms of improvement of nearly 8% in head yield. The time-based study indicated that grain kernel fissures were not present although breakage still occurred in the samples. Comparison of the strength characteristics from the time-based study with those of the main experiment showed that improvement of strength characteristics persisted for several weeks. A delay of approximately three weeks prior to milling was considered appropriate to realize optimum milled rice yields. The grain quality index developed in this study corroborated the results of the main experiment in ranking the treatments on a basis of preferred characteristics for the end product.

Pages

174

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