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United States Department of Agriculture

Agricultural Research Service

Research Project: New Sustainable Processing Technologies to Produce Healthy, Value-Added Foods from Specialty Crops and their Co-Products

Location: Healthy Processed Foods Research

Title: Effect of milling temperature and post-milling cooling procedures on rice milling quality appraisals

Authors
item Pan, Zhongli
item Khir, Ragab -
item Thompson, James -

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 8, 2012
Publication Date: May 1, 2013
Citation: Pan, Z., Khir, R., Thompson, J.F. 2013. Effect of milling temperature and post-milling cooling procedures on rice milling quality appraisals. Cereal Chemistry. 90(2):107-113.

Interpretive Summary: There is a great need to quantitatively understand the effects of milling conditions and post-milling handling procedures on the milled rice temperature, moisture loss, cooling rate, single and multiple fissuring rates that eventually affect milling quality. This study showed that the improper milling conditions significantly reduced appraised milling quality of rough rice. However, milling under cooling with ice water and room temperature water significantly reduced milled rice temperatures, and single and multiple fissuring rates, but improved head rice yield (HRY). Additionally, suitable post-milling cooling procedures led to improved milling quality. Open container and pan cooling methods are not recommended since they had more moisture losses and resulted in lowered appraised quality than closed container cooling. Integrated positive effect for milling under cooling conditions followed by closed container cooling improved total rice yeild (TRY) and head rice yield (HRY) by 0.9 and 1.5 percentage points, respectively. There was no significant effect of milling temperature and post-milling cooling conditions on WI and TLC. To accurately and reliably appraise rice milling quality, it is concluded that milling under cooling conditions followed by closed container cooling should be applied.

Technical Abstract: The objective of this research was to study the effects of different milling conditions and post-milling handling procedures on appraised milling quality of rough rice. Samples of medium grain rough rice (M202) with moisture content (MC) of 11.5±0.2% were used for this study. To create different milling temperatures, the samples were milled with McGill No. 3 mill under four milling conditions, including normal milling, milling at high temperature, milling with cooling using ice water and room temperature water as a cooling media. The milled rice samples were cooled in closed and open plastic containers, and open pans with three temperatures, 15, 23, and 35°C. The effects of milling and post-milling conditions on milled rice temperature, moisture loss, cooling rate, single and multiple fissuring rates, total rice yield (TRY), head rice yield (HRY), Whiteness Index (WI), and total lipid content (TLC) were evaluated. Results showed that high single and multiple fissuring rates and low TRY and HRY were inherent in improper milling and post-milling conditions. The averages of single fissuring rates were 15.9 and 17.6% for rice samples milled under normal and high temperature of milling conditions, respectively. The corresponding values of multiple fissuring rates were 3.5 and 7.2 %. Cooling methods using open containers and pans had more moisture losses and further resulted in lowering appraised milling quality than in the closed containers. The low temperature milling conditions followed by cooling in closed containers significantly reduced single and multiple fissuring rate and improved TRY and HRY by 0.9 and 1.5 percentage points, respectively. The effects of tested milling and post-milling conditions on WI and TLC were not significant. Obtained results constitute valuable information for developing the milling and cooling procedures to achieve consistent, accurate and reliable milling quality appraisals for rough rice.

Last Modified: 7/28/2014
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