Drying Characteristics and Milling Quality of Rough Rice Dried in a Single Pass Incorporating Glass Transition Principles

Abstract

The objective was to study the drying characteristics and milling quality of rough rice subjected to single-pass drying while controlling kernel material states. Drying experiments were conducted at 60, 70, and 80°C and relative humidities ranging from 13 to 83%. For all drying air temperatures and tempering conditions, milling quality was not significantly different from the controls when the relative humidity of the drying air was maintained above 63% (kernel core and surface maintained in a rubbery state) and rice was tempered immediately after drying, in sealed plastic bags and at the drying air temperature, for at least 60 min.

Keywords:

• Drying
• Glass transition
• Relative humidity
• Single pass
• Tempering

Notes

Immediately after drying, the samples were exposed to ambient air for 0, 60, 120, and 180 s before tempering in sealed plastic bags for 60 min, after which they were spread in thin layers and exposed to ambient air for 10 min. Head rice yields are an average of four measurements; that is, two replications with each replicate head rice yield measured in duplicate. Head rice yields are statistically compared within rows. Significant differences between sample means were established using Tukey's test at α = 0.05. Values designated by the same superscript letter are not significantly different.

The empirical constants A, B, and C of the modified Chung–Pfost equation were estimated by Ondier and Siebenmorgen.^{[ 33 ]}