INFLUENCE OF RICE SAMPLE PREPARATION AND MILLING PROCEDURES ON MILLING QUALITY APPRAISALS

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%+/- 10.3% (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.