https://espace.library.uq.edu.au/view/UQ:372893/UQ372893_OA.pdf

The importance of amylose and amylopectin fine structure for textural properties of cooked rice grains

Starch molecular structure: The basis for an improved understanding of cooked rice texture.

The term rice quality means different things to different people. To some it refers to the quantity of whole kernels remaining after milling (aka polishing), to others it is the visual appeal of the rice after milling, and then some use it to mean the eating quality or palatability of rice compared to local preferences. The term end-use quality is used in this chapter to encompass all of those definitions for rice quality plus the addition of others. Specifically, rice end-use quality is defined here to include its cooking, processing, physicochemical and functional properties, as well as its sensory, nutritional, and bioactive characteristics. This chapter focuses on the analytical methods and instruments available to measure the first three of these properties of rice, that is cooking, processing, physicochemical, and functional properties.

Rice End-Use Quality Analysis

Parboiled rice: Understanding from a materials science approach

A study was made of factors affecting cooking time and the relationship between water:rice ratio (water content) in the rice cooker method and Instron hardness of cooked rice using 10 milled rice samples of diverse properties. Water:rice ratio for acceptable soft texture (< 10 kg hardness) increased with increasing amylose content of the sample from 1.1 (56% water in cooked rice, wet basis) to 1.9 (68% water). The spread in cooked-rice hardness values was higher at a water:rice ratio of 1.9 (68% water) than at 2.65 (75% water), which was equivalent to the water content of rice cooked in excess water for an optimum cooking time. Cooking time correlated better with starch final gelatinization temperature (r=0.75*) than with surface area per gram (r=−0.49) confirming the results of earlier kinetic studies that cooking rate was mainly influenced by the reactivity of the grain constituents with water.

Major factors affecting cooked milled rice hardness and cooking time

The texture of 10 milled rices cooked by a standardized method in excess water was measured in 11 laboratories using various instrument methods that had been developed specifically for national samples. The samples selected represented a wide range of rice textures. Instrument indexes for hardness and stickiness of cooked rice generally were more sensitive than the corresponding taste panel scores in discriminating among the 10 cooked rice samples. Instrument indexes for hardness correlated positively among each other as did those for stickiness. Most hardness indexes showed significant negative correlation with stickiness indexes. Most hardness indexes were positively correlated with amylose content whereas stickiness indexes were negatively correlated with amylose content. The continued use of amylose content as an index of eating quality in a rice breeding program is justified.

Jun'ichi Shiki

Papers

International cooperative comparison of instrument methods for cooked rice texture