RICE QUALITY AND PROCESSING Functional Properties of Commingled Rice-Cultivar Lots

Commingling of rice cultivars commonly occurs during harvest, drying, and storage operations. As different cultivars often have different functional properties, there is a need to study the impact of commingling on these properties. Two long-grain, hybrid cultivars, Clearfield (CL) XL745 and CLXL729, and two long-grain, pure-line cultivars, CL151 and Wells, were used to prepare hybrid/pure-line, hybrid/hybrid, and pure-line/ pure-line commingles in various proportions. Gelatinization and pasting properties, as indicators of functional performance, were measured for all individual lots and commingled samples. When two cultivar lots with different onset gelatinization temperatures (Tos) were commingled, the To of the commingled sample was similar to the To of that cultivar in the commingle with the lower To. Other gelatinization properties, as well as peak, breakdown, and final viscosities of commingled samples generally increased or decreased according to the mass percentages of the cultivars in the samples. INTRODUCTION Gelatinization and pasting properties of rice have a significant impact on enduse applications. These properties can differ among cultivars, impacting final product characteristics and process costs when manufacturing on an industrial scale (Juliano, 1998). Gelatinization is a process in which starch undergoes order-disorder transitions with the application of heat to kernels that have been soaked (Sivak and Preiss, 1998). Determining the temperature and energy required for gelatinization is therefore of particular importance to food processors who need to optimize cooking conditions and reduce process costs (Bao and Bergman, 2004). After becoming gelatinized, starch granules form a paste comprising a viscous material of starch granules and leached AAES Research Series 626 322 starch molecules. Thus, pasting properties are important indicators of cooking behavior of starch and final product quality (Manaois, 2009). Commingling of rice cultivars commonly occurs during harvest, drying, and storage operations. As different cultivars often have different starch structure and milling properties (Siebenmorgen et al., 2006), commingling could impact functional properties, particularly when dissimilar cultivars are commingled. PROCEDURES The study was conducted using four long-grain cultivars, CLXL729 and CLXL745 (hybrids), and CL151 and Wells (pure-lines), each grown at various locations in Arkansas in both 2011 and 2012. The 2011 lots were selected to have high head rice yields (HRYs), while the 2012 lots were selected to have lower, in order to determine if commingling had a similar effect on rice of different levels of milling yield. All lots were cleaned using a dockage tester (Model XT4, Carter-Day Co., Minneapolis, Minn.) and conditioned to 12 ± 0.5% (wet basis) moisture content. Samples from the cultivar lots were commingled in various ratios as presented in Table 1. To prepare for milling, 150-g rough rice samples were prepared for each commingling ratio. The masses of the individual cultivars in the commingled samples were 15/135 g, 38/112 g, 75/75 g, 112/38 g, and 135/15 g, respective to the 10:90, 25:75, 50:50, 75:25, and 90:10 commingling ratios. The individual lots of rough rice were first divided into a close approximation of the required quantities using a grain divider (Boerner Divider, Seedburo Equipment Co., Chicago, Ill.), weighed accurately to the above-mentioned values, and thoroughly mixed. Each 150-g rough rice sample was first dehulled in a laboratory sheller (THU 35B, Satake, Hiroshima, Japan), then milled using a laboratory mill (McGill No. 2, RAPSCO, Brookshire, Texas), having a 1.5-kg mass placed on the lever arm, 15 cm from the centerline of the milling compartment. Head rice was then separated from brokens using a sizing device (Model 61, Grain Machinery Manufacturing Corp., Miami, Fla.). Surface lipid content (SLC) of head rice was measured using a lipid extraction system (Soxtec Avanti 2055, Foss North America, Eden Prairie, Minn.). Individual-cultivar lots and commingled samples that had been milled for durations that produced a degree of milling (DOM) closest to 0.4% SLC, a typical industry standard, were used for measuring gelatinization and pasting properties. Gelatinization properties of samples were measured using a differential scanning calorimeter (DSC) (Diamond, Perkin-Elmer, Shelton, Conn.). Samples of head rice (20 g) were ground using a cyclone mill (3010-30, UDY, Fort Collins, Colo.), equipped with a 100-mesh (0.5-mm) sieve. The DSC cycle comprised heating from 25 °C to 120 °C at a rate of 10 °C/min. Data output was in the form of a thermogram, in which the temperature at which gelatinization started (To), peaked (Tp), and concluded (Tc), as well as the energy required to gelatinize (ΔH), were determined by DSC system software (Pyris Data Analysis, Perkin-Elmer, Shelton, Conn.). Pasting properties of rice flour were measured using a Rapid Viscoanalyser (RVA) (model 4, Newport Scientific, Warriewood, NSW, Australia). Exact amounts of flour