Structure of rice starch and its relation to cooked-rice texture

Black rice is well known as healthy food. Nowadays, some people try to change their diet with this rice. However, it still has a problem with long preparation time and hard texture. Parboiling is a hydrothermal process that changes rice starch from crystalline to amorphous. The parboiling process of rice consists of soaking in sodium citrate solution, high-pressure cooking, freezing-thawing and drying. The aim of this research was to find the optimum condition from three processing variables: concentration of sodium citrate (0, 2, 5 and 5%, w/v), cooking period in an autoclave (5, 10 and 15 min) and a number of freeze-thaw cycles (1, 2.5 and 4). The optimum condition was achieved with 3.8% sodium citrate concentration, 5 min cooking in an autoclave, and 3.8 freeze-thaw cycles. This optimum condition resulted in parboiled black rice with 25.84 min cooking time, 4.93 total colour difference 101.80 N hardness of cooked rice, 49.04 N chewiness of cooked rice, 5.32 kg rice grain hardness.

Download Full-text

High-amylose Rice: Starch Molecular Structural Features Controlling Cooked Rice Texture and Preference

Proceedings ◽

10.3390/proceedings2019036082 ◽

2020 ◽

Vol 36 (1) ◽

pp. 82

Author(s):

Tao ◽

Yu ◽

Sangeeta ◽

Gilbert

Keyword(s):

Amylose Content ◽

Structural Characteristics ◽

Starch Synthesis ◽

Rice Flour ◽

Structural Features ◽

Size Exclusion ◽

Rice Starch ◽

Eating Quality ◽

Cooked Rice ◽

High Amylose

Cooked high-amylose rices have slower digestibility, giving nutritional benefits, but inferior eating qualities. In this study, Rapid Viscosity Analysis, quantitive descriptive sensory analysis with all panellists from China and Textural Profile Analyser (TPA) have been used to measure rice texture and eating quality of cooked rice. Molecular structural mechanisms for this inferior eating quality are found here using structural analysis by size-exclusion chromatography of both the parent starch and starch leached during cooking. All commonly-accepted sensory attributes of cooked rice were characterized by a trained human panel. Hardness, with the strongest negative correlation with panelist preference, is the dominant but not sole factor determining palatability. Rice with larger amylopectin size can bond more water, thereby have lower hardness value. Meanwhile, hardness is controlled by the amounts of medium and long amylopectin chains and amylose in the starch, and by amylose content and amount of longer amylopectin chains in the leachate. With this, it is concluded for the first time that rice containing 19~ 25% amylose content are most preferred by the panel. Meantime, it is showed that breakdown viscosity and swelling power of native rice flour can be and should be used as indicators for predicting rice eating quality. This gives knowledge and understanding of the molecular structural characteristics of starch controlling cooked-rice preference: not just high amylose but also other aspects of molecular structure. This can help rice breeders to target starch-synthesis genes to select slowly digested (healthier) rices with acceptable palatability.

Download Full-text