Sarah B. Lanning

Impacts of Preharvest Factors During Kernel Development on Rice Quality and Functionality

Rice quality and functionality are characterized in many ways, depending largely on the industry segment using the rice. These characteristics include appearance, milling, and cooking parameters. Recently, variable quality of rice grown in the United States has been reported, but the cause was not well documented. Agronomic impacts include planting time, irrigation and fertility, cultivar selection, and harvest conditions. However, recent research suggests that ambient air temperature, specifically elevated nighttime air temperature (NTAT) during grain filling, dramatically affects the variability of rice milling quality, in terms of milled- and head-rice yields; appearance, in terms of chalkiness; and functional characteristics, including viscosity profiles, gelatinization temperatures, and proximate concentrations. Future research is needed to develop cultivars that are resistant to stress resulting from elevated NTAT during the critical period of grain filling, and, for the near term, to develop altered production management practices that mitigate elevated-temperature stress.

Comparison of Milling Characteristics of Hybrid and Pureline Rice Cultivars

Milling characteristics vary among rice cultivars due to inherent differences in physicochemical properties. Hybrid cultivars have gained popularity due to their favorable production performance, but may exhibit different milling characteristics than pureline cultivars. A study was conducted to compare milling characteristics of two long-grain, pureline cultivars (Wells and Francis) and four long-grain, hybrid cultivars [XL723, Clearfield (CL) XL729, CL XL730, and CL XL745]. Rough rice samples of each cultivar were conditioned to 12.5% moisture content (MC) (w.b.) prior to milling, and sub-samples of four cultivars (Wells, Francis, CL XL729, and CL XL745) were conditioned to 10.5%, 11.5%, and 13.5% MC in order to evaluate the effect of MC at time of milling. Samples were milled for durations of 10, 20, 30, and 40 s. Results showed that hybrids generally reached the target surface lipid content (SLC) in a shorter duration than purelines, and that the color of hybrid head rice was generally whiter and less yellow than purelines after milling for any duration. Slopes of head rice yield (HRY) versus SLC, indicating the rate of change in HRY per unit change in SLC, varied significantly among cultivars. Milling MC had an effect on milling curves, in that rice milled at greater MC exhibited lesser SLC values and greater rates of change in HRY with respect to SLC than rice milled at lesser MC. The findings indicate a need to consider SLC in order to equitably compare milling performance and functional properties of different rice cultivars.

Effects of Nighttime Air Temperature During Kernel Development of Field-Grown Rice on Physicochemical and Functional Properties

ABSTRACT Elevated nighttime air temperatures (NTATs) occurring during critical grain-filling stages affected rice physicochemical properties, which impacted functional quality. Six cultivars were grown at multiple field locations from northern to southern Arkansas during 2007 to 2010. Nighttime temperatures were recorded throughout production at each of the locations, and 95th percentiles of NTATs were calculated for each cultivars reproductive (R) stages. Amylose content and crude protein content decreased linearly, whereas total lipid content increased linearly, with increasing NTATs occurring during the grain-filling stages (R6–R8). Effects of NTAT on proximate composition influenced functional properties. Peak viscosities increased linearly as NTAT increased, whereas setback viscosities decreased. Setback viscosities were linearly correlated to NTATs for medium-grain cultivars, but correlations were quadratic for the long-grain cultivars. Gelatinization temperatures increased linearly with increasing...

Impact of Elevated Nighttime Air Temperatures During Kernel Development on Starch Properties of Field-Grown Rice

ABSTRACT The structural features of starch were examined to better understand the causes of variability in rice quality resulting from nighttime air temperature (NTAT) incidence during kernel development. Starch samples were isolated from head rice of four cultivars (Bengal, Cypress, LaGrue, and XL723) field-grown in four Arkansas locations (Keiser, Pine Tree, Rohwer, and Stuttgart) in 2009 and 2010. Average NTATs recorded during the grain-filling stages of rice reproductive growth in the four locations were 3.0–8.4°C greater in 2010 than 2009. Elevated NTATs altered the deposition of starch in the rice endosperm. Means pooled across cultivars and locations showed that amylose content was 3.1% (percentage points) less for the 2010 sample set. The elevated NTATs in 2010 resulted in a decrease in the percentage of amylopectin short chains (DP ≤ 18) and a corresponding increase in the percentage of long chains (DP ≥ 19) by an average of 1.3% (percentage points). The greater NTATs in 2010 also produced greate...

Effects of Preharvest Nighttime Air Temperatures on Whiteness of Head Rice

ABSTRACT The effects of nighttime air temperature (NTAT) on the color of milled rice were investigated. Elevated NTATs occurring during the critical grain-filling stages of kernel development impacted the color of head rice. Six cultivars, grown at multiple field locations from northern to southern Arkansas during 2007–2010, were evaluated for head rice color, using whiteness (L*) and yellowness (b*) indices, and for chalk. Nighttime temperatures were recorded throughout production at each of the selected locations, and the 95th percentiles of NTAT frequencies (NT95) were calculated for each cultivars reproductive (R) stages. Head rice color values were analyzed in relation to NT95 occurring during the grain-filling (R6–R8) stages and in relation to percent chalkiness. Whiteness generally increased with increasing NTAT and with increasing chalkiness. Yellowness decreased as chalkiness increased. Moreover, kernel whiteness increased even when measured in the absence of chalky kernels, suggesting that star...

A Review of Hygroscopic Equilibrium Studies Applied to Rice

Equilibrium moisture content (EMC)/equilibrium relative humidity (ERH) studies pertaining to rice and rice products were reviewed. Methods of determining rice and rice component EMC/ERH data varied, using procedures involving static and dynamic equilibration methods, as well as direct gravimetric methods and indirect ERH-measurement methods. Methods for measuring rice and rice component moisture contents also varied. The Modified Henderson and Modified Chung-Pfost equations were most frequently recommended for predicting the sorption behavior of rice. Among rough rice components, for any given temperature and relative humidity, the EMC of milled and brown rice were consistently the greatest, generally followed by rough rice, bran, and hull. The hysteresis effect was apparent in rice. The magnitude of hysteresis decreased with repeated cycles of drying and rewetting and with increasing temperature. EMC/ERH relationships were affected by rice cultivar, but harvest location was not a significant factor. As such, in order to be most accurate, EMC/ERH equations for each rice cultivar need to be determined.