|RAGAB, KHIR - University Of California|
|THOMPSON, JAMES - University Of California|
Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2013
Publication Date: 4/1/2013
Citation: Ragab, K., Pan, Z., Thompson, J.F. 2013. Influence of rice sample preparation and milling procedures on milling quality appraisals. Transactions of the ASABE. 56(3):1051-1060.
Interpretive Summary: Improving the consistency and accuracy of rice milling appraisals is an increasingly important goal in the rice industry, as the monetary value of a rice lot is appraised based on its milling quality. In the U.S., the milling process is typically conducted according to the official procedures of the USDA Federal Grain Inspection Service. These standards mainly specify procedures for milling dried rice. There is no documented information on the procedures neither for preparing rice samples nor for the time required to store dried rice samples that are to be used in milling quality appraisal. Head rice yield was significantly affected by variation in initial MC, drying temperature, storage time after drying, and milling procedure. It decreased significantly with increased initial MC and drying temperature. The low-temperature milling and normal milling procedures significantly improved head rice yield up to 4.8% and 2.8%, respectively. Head rice yield significantly increased with increase in storage time of dried rice up to four days, after which it was not affected by storage time. This research documents development of a standard methodology for sample preparation in order to achieve consistent and reliable milling quality appraisals.
Technical Abstract: The objective of this research was to investigate the effect of sample preparation and milling procedure on milling quality appraisals of rough rice. Samples of freshly harvested medium-grain rice (M202) with different initial moisture contents (MCs) ranging from 20.2% to 25.1% (w.b.) were used for this study. To create rough rice with varying quality, the samples were dried from their initial MC to a moisture content of 13.1% ±0.3% (w.b.) using air at different temperatures. Before milling, the MC of the samples was measured using three different methods: standard oven method, Dickey-John GAC 2100 (DKJ), and single-kernel moisture meter (SKM). The samples were milled using a McGill No. 3 mill. Three milling procedures were used: the standard western milling procedure, referred to as normal milling (NM), the southern milling procedure (SMP), and low-temperature milling (LM). The effect of storage after drying on quality appraisals was evaluated. Milling quality was compared based on total rice yield (TRY), head rice yield (HRY), whiteness index (WI), and lipid content (LC). HRY was found to be significantly affected by variation in initial MC, drying temperature, storage time after drying, and milling procedure. WI and LC were not significantly affected by these parameters. HRY decreased significantly with increased initial MC and drying temperature. The LM and SMP procedures significantly improved HRY up to 4.8% and 2.8%, respectively. HRY significantly increased with increase in storage time of dried rice up to four days, after which HRY was not affected by storage time. Regression models were successfully developed to predict HRY under tested rice conditions and milling procedures. The DKJ and SKM instruments, which are widely used in the rice industry, need to be calibrated at the full moisture range to ensure accurate results in MC measurement. The obtained results provide valuable information to achieve consistent, accurate, and reliable milling quality appraisals.