Date of Graduation

8-2023

Document Type

Thesis

Degree Name

Master of Science in Food Science (MS)

Degree Level

Graduate

Department

Food Science

Advisor/Mentor

Griffiths Atungulu

Committee Member

Rusty Bautista

Second Committee Member

Andronikos Mauromoustakos

Third Committee Member

Dongyi Wang

Keywords

Fissures;Rice;Seed germination;Seed rice;Seed vigor;X-ray imaging

Abstract

Improper drying, which causes fissuring of rice kernels, may influence the overall seed health. This study evaluated the impacts of various drying conditions on rice fissures, seed germination and vigor. A long – grain rice cultivar with a moisture content (MC) of 15.5% w.b. (wet basis) was used during the experiments. Samples were dried as thin layers at temperatures of 30 ℃, 40 ℃ and 50 ℃ with a constant relative humidity (RH) of 50% and air velocities (AV) of 0.66 m/s and 1.65 m/s. X – ray imaging was used for fissure detection before and after drying the samples to 13.5% MC w.b. prior to germination and vigor tests. The results correlated drying condition, fissuring intensity, seed germination (SG), and seed vigor (SVI). Findings at 50% RH showed that fissure increased with increase in temperature from 30 ℃ to 50 ℃ for high and low AV, with more intensity recorded at 1.65 m/s. Accordingly, the rise in temperature did not affect germinability of the seeds, with a similar trend observed at both AVs. Having established that the drying boundaries considered had no impact on SG, we hypothesized that the extent of the impact may depend on the type of fissure and its proximity to the germ, where the plant sprouts. For this experiment, two long-grain hybrid cultivars each with two harvest moisture content (HMC) levels ranging from medium (19 – 21%) to high (22 – 24%) wet basis (w.b.) were used. Samples were dried to 12.5% MC w.b. and fissures were induced at air temperature of 60 ℃ and 25% RH and classified based on fissure types and proximity to the germ, with kernels without fissures identified as control samples. Cultivars had the most statistically significant effect on SG and SVI, suggesting that these parameters strongly depend on the rice cultivar used. Fissure classification based on proximity to the germ had no significant effect on the parameters, because the detected fissures were not located very close to the germ. Conversely, since the fissure types identified between the high and medium MC seeds were distinct, fissure types had a significant effect on SG and SVI. Furthermore, we predicted that SG and SVI may be influenced by variations in the drying characteristics exhibited by varying kernel thicknesses within the panicles. To investigate this, two long-grain hybrid cultivars with medium (19 – 21%) and low (15 – 17%) MC were utilized. These samples were size fractionated into thick (> 2.03 mm) and (thin 1.91>>2.03 mm), with non-fractionated samples as the control. Samples were dried to 12.5% MC w.b. at temperatures of 40 ℃ and 60 ℃ with 25% RH, after which seed germination and vigor tests were performed. Thick kernels had significantly higher seed germination (SG) than thin kernels, but there was no significant difference when compared to unsorted kernels. Overall, these findings help to quantify the importance of rice drying and fissure classifications, as well as highlight the role of kernel thickness grading as it relates to seed germination and vigor.

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