course:grain quality module 6: determining the chemical characteristics of milled rice

Course : Grain QualityModule 6 : Determining the Chemical Characteristics of Milled RiceLesson 1 : What are the three chemical characteristics of milled rice that determine quality?

Gel consistency measures the tendency of the cooked rice to harden on cooling.

Gelatinization temperature determines the time required for cooking the rice

High amyclose content?Rice grains cook dry, are less tender, and become hard upon cooling.

Low-amylose content?Rice grains cook moist and are sticky


• Alkali test • Amylose test • Gel consistency test • Kernel elongation test • Aroma test

FREQUENTLY ASKED QUESTIONS (FAQs)

1. What are the specific physicochemical tests used to determine the cooking and eating qualities of rice?

The appearance of milled rice is important to the consumer, which makes it also important to the producer and the miller. The consumer prefers rice with a clear endosperm and pays a premium rice for it, even though capacity disappears during cooking and does not affect eating quality. Grain with opaque areas in the endosperm, caused by the loose packing of the starch and protein particles, breaks more readily during milling than clear grain, greatly reducing its market value.


2. Why is endosperm appearance a major breeding consideration?


Most breeders attempt to estimate the milling behavior of pedigree selections n the basis of grain length and shape and on endosperm appearance. Grain traits that contribute to increased breakage, singly and in combination with other traits, include grain length, excessively slender or bold shape, partial flatness, and appreciable white belly.


3. Of what importance are grain length, shape and endosperm appearance to the breeder?


It allows the breeders, in certain cases, to use the simple gelatinization temperature test to estimate the amylose content, which is considerably more difficult to measure directly.


4. How does the limited association of gelanization temperature and amyclose content help the breeders?


Gelatinization temperature directly affects the physical properties of the starch granule, which in turn influences the quality ratings of cooked rice. Rice with a high gelatinization temperature becomes excessively soft and tends to disintegrate when overcooked. Under standard cooking procedures, this type of rice tends to remain undercooked. It requires more water and time to cook than those with low or intermediate gelatinization temperature. Thus, gelatinization temperature correlates positively with the time required to cook rice. Soaked milled rice of high gelatinization temperature elongates less during cooking than rices with low or intermediate gelatinization temperature.


5. How is gelatinization temparature related to the physical cooking properties of rice?


Varietal differences in gel consistency exist among varieties of similar high amylose content (more than 25%). The gel consistency test separates the high-amylose rices into three categories:

• very flaky rices with hard gel consistency (length of gel = 40 mm or less)

• flaky rices with medium gel consistency (length of gel = 41 to 60 mm)

• soft rices with medium gel consistency (length of gel > 61 mm).


6. Why test for gel consistency?


Aging increases water absorption and volume expansion during cooking, resulting in a more flaky cooked rice than freshly harvested grains.


7. Why should paddy rice be stored for at least 4 months after harvest before tasting panels evaluate promising lines?


Course : Grain QualityModule 6 : Determining the Chemical Characteristics of Milled Rice Lesson 2 : Why is amyclose content important and how is it measured?

If then

Amylose content is high,

the rice grains will show high volume expansion (not necessarily elongation) and a high degree of flakiness. The rice grains cook dry, are less tender, and become hard upon cooling.

Amylose content is low,

the rice grains will cook moist and sticky.

Course : Grain QualityModule 6 : Determining the Chemical Characteristics of Milled RiceLesson 2 : Why is amyclose content important and how is it measured?

10-20% amyclose content is classified as Low

25% amyclose content is classified as Intermediate. Intermediate amyclose rice is preferred in most rice-growing areas of the world except where low -amyclose japonicas are grown.

20-30% amyclose content is classified as High

CLASSIFICATION RANGES

Course : Grain QualityModule 6 : Determining the Chemical Characteristics of Milled Rice Lesson 3 : Why is gelatinization temperature important and how is it measured?

Gelatinization Gelatinization temperature determines temperature determines the amount of time it the amount of time it takes for a particular takes for a particular variety of rice to cook.variety of rice to cook.

LowVarieties with a gelatinization temperature below 70°C. Most Japonica varieties have a low gelatinization temperature.

IntermediateVarieties with a gelatinization temperature between 70°C – 74°C. Most tropical Indica varieties have intermediate or low gelatinization temperature.

HighVarieties with a gelatinization temperature greater than 74°C. If GT is very high, then the rice will become excessively soft and disintegrate when overcooked. It will also require more cooking and water than rice with a lower GT.

Course : Grain QualityModule 6 : Determining the Chemical Characteristics of Milled RiceLesson 3 : Why is gelatinization temperature important and how is it measured?

Course : Grain QualityModule 6 : Determining the Chemical Characteristics of Milled RiceLesson 4 : Why is gel consistency important and how it is measured?

If then

Gel consistency is hard,

the cooked rice tends to be less sticky. Harder gel consistency is associated with harder cooked rices and this feature is particularly evident in high-amylose rice.

Gel consistency is soft,

the cooked rice has a higher degree of tenderness. This is a preferred characteristic

Classification Length of gel (mm)

Hard 27-35

Medium Hard 36-40

Medium 41-60

Soft 61-100

Gel consistencyHard and soft gel consistencies

course:grain quality module 6: determining the chemical characteristics of milled rice

Documents

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rice grains

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type of rice

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qualities of rice

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