Chalkiness in Rice

Prelims – Current events of national and international importance | Science & Technology.

Why in News?

Recently, scientists in China discovered a gene that helps prevent rice grains from breaking during milling.

Layers of Rice

Husk – The outermost layer of the rice that has to be removed.
Bran – It is inside of husk that is also removed to whiten the rice.
Removal of layers – Traditionally, these were removed by pounding the paddy rice with grinders in a mortar, then winnowing the grains from the chaff.
Currently, mechanical rollers graze the layers by a process called milling.

Chalkiness – It is a trait found in rice grains that significantly increases breakage during milling.
Chalky grain rate – It is measured by the proportion of chalky grains among all rice grains and the degree of chalkiness, which reflects the extent of chalkiness in them.
Properties – Chalky rice grains have an opaque appearance after milling and a brittle structure, which leads to higher breakage during milling.
Determinants – Chalkiness in rice varieties is influenced by many genes and by environmental factors like high temperature and nutrient availability.
Small stretch DNA on chromosome 9
- If present - Strongly associated with low chalkiness
- If absent – It is associated with high chalkiness.
Low-chalkiness varieties showed higher expression of Chalk9 in endosperms compared to high-chalkiness varieties.

The endosperm is the part of the paddy grain that makes up the bulk of the milled rice.

Impact - Higher chalkiness leads to more breakage during milling, reduces the yield and affects rice quality.
It disappears during cooking and does not affect the taste & aroma.
Modern breeding technique – It has selected for the low-chalkiness version (Chalk9-L), improving rice quality over time.
Breeders can directly introduce the Chalk9-L variant into high-chalkiness varieties to reduce breakage and enhance grain quality.

Reference

The Hindu| Chalkiness in Rice