Changes in Cracking Behavior and Milling Quality of Selected Australian Rice Varieties Due to Postdrying Annealing and Subsequent Storage

Abstract

This study investigated the effect of drying temperatures, annealing regimes, and storage conditions on the level of rice kernel fissuring, mechanical strength, and head rice yield of three Australian-grown rice varieties, namely, Kyeema (long grain), Amaroo, and Reiziq (medium grains). Paddy samples were dried at 40, 60, and 80°C and then annealed for 0, 40, 80, and 120 min at the same drying temperature. It was found that annealing slightly improved the head rice yield with an increase in stiffness of rice kernels. The number of fissured kernels decreased with prolonged annealing duration of 80–120 min. During the storage period of up to 4 months at 4, 20, and 38°C, all measured parameters, such as percentage of fissured kernels, hardness, stiffness, head rice yield, and pasting properties, also showed increasing trends. A relatively rapid change in these physical properties of all rice samples was observed during storage at 38°C. A significant increase in stiffness of rice during storage at 38°C suggested that physical aging occurs during storage of rice below its glass transition temperature (55°C).

Keywords:

• Annealing
• Drying
• Mechanical strength
• Milling quality
• Rice
• Storage
• Tempering

ACKNOWLEDGMENTS

The authors are grateful to the Collaboration for Agriculture and Rural Development (CARD) Program, Vietnam, for providing funding support for this study. CARD is an AusAID-funded project for Vietnam to promote agriculture and rural development through the application and adaptation of research, technology, skills, and management practices with a focus on smallholders.

Notes

^a Brown rice–based measurements.

^b Milled rice flour analyses.

All data are mean values ±standard deviations. The same superscripts in the same row indicate no significant difference at P > 0.05.

δ = drying temperature; τ = annealing time.

All values are means ±standard deviations. The same superscripts in the same column indicate no significant difference at P > 0.05.

^a SE mean is computed as the pooled standard error mean for each variety. The same superscripts in the same row indicate no significant difference at P > 0.05.

^a SE mean is computed as the pooled standard error mean for each variety.

The same superscripts in the same column indicate no significant difference at P > 0.05.

Δ = drying temperature; δ = storage temperature; τ = storage duration.

All values are means of two measurements. Pooled standard deviations for each value are expressed in the same column.

The same superscripts in the same column indicate no significant difference at P > 0.05.

All values are means ±standard error.