Date of Graduation

12-2013

Document Type

Thesis

Degree Name

Master of Science in Food Science (MS)

Degree Level

Graduate

Department

Food Science

Advisor

Terry J. Siebenmorgen

Committee Member

Ya-Jane Wang

Second Committee Member

Andy Mauromoustakos

Keywords

Biological sciences; Fissuring; Grain; Hybrid; Milling; Pureline; Rice

Abstract

Over the past decade, the use of hybrid rice cultivars has greatly increased, and this has led to questions about the processing behavior of hybrid cultivars. This study compares the milled rice fissuring kinetics of hybrid and pureline cultivars. Also, this study elucidates the effects of kernel type (long-grain vs. medium-grain rice cultivars), surface lipid content (SLC), and kernel thickness on fissuring rates.

Three hybrid (CL XL745, CL XL729 and XL753) and five pureline (Wells, CL151, Cheniere, Jupiter and CL261) cultivar lots were procured. Jupiter and CL261 are medium-grain cultivars, whereas the rest are long-grain cultivars. Two experiments were conducted. Experiment 1 quantified the number percentage of fissured kernels of all eight cultivar lots; samples were milled to a SLC of 0.4%, and then exposed to air temperatures of 10°C and 30°C and relative humidities (RHs) of 10, 20, 50, 80 and 90%. Percent fissured kernels were recorded at durations of 4, 8, 16, 32, 60 and 120 min. Experiment 2 quantified the number percentage of fissured kernels of CL XL745 and CL151 cultivar lots; samples of both lots were milled to SLCs of 0.2, 0.4, 0.6, and 0.8%, and then exposed to an air temperature of 30°C and RHs of 20 and 80%. Percent fissured kernels were recorded at 4, 8, 16, 32, 60 and 120 min. In addition, the number percentage of fissured kernels of thin-, medium-, and thick-kernel fractions were exposed to these same air conditions and then analyzed.

When exposed to low- and high-RH air, some hybrid long-grain (H-L) cultivar lots fissured less than some pureline long-grain (P-L) cultivar lots and vice versa. Of the H-L cultivar lots, XL753 significantly fissured the least, and of the P-L cultivar lots, CL151 and Wells significantly fissured less than Cheniere. Initial fissuring rates were greater at 30°C than 10°C, and greater at 10% RH than 90% RH. On average, pureline medium-grain (P-M) cultivar lots were found to significantly fissure more than long-grain cultivars; and at 10°C and RHs of 20 and 90%, milled rice from the hybrid long-grain cultivar group fissured significantly less than the pureline long-grain cultivar group. All other conditions showed no significant difference between the mean percent fissured kernels of H-L and P-L cultivar groups. As for SLC and kernel thickness, significant differences in fissuring rates were seen among SLCs. As SLC decreased, an increase in percent fissured kernels was seen. No significant differences in percent fissured kernels were seen among thin-, medium- and thick-kernel fractions.

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