Rice Grain Quality By JF Rickman and M

Rice Grain Quality By JF Rickman and M Gummert, IRRI, Los Banos Philippines

What is rice quality? Rice quality is a combination of physical and chemical characteristics which are required for a specific use by a specific user.

Genetic Properties • • Chemical characteristics Shape Size Color Chalkiness Bulk density Thermal conductivity Equilibrium Moisture Content • Flow ability

Acquired properties • • • Moisture content Grain purity Pest damage Physical damage Immature grains Milling characteristics • Chalkiness

Quality Characteristics Genetic Acquired • chemical characteristics such as gelatinization temperature, gel consistency, and aroma • moisture content • grain shape and size • color and chalkiness • bulk density • purity • thermal conductivity • damage • equilibrium moisture content • cracked grains • immature grains • milling-related characteristics (head rice recoveries, whiteness and milling degree) are also included as relevant measures of quality because they are of concern to consumers

Paddy rice characteristics • • Moisture content Degree purity Varietal purity Grain dimensions Cracked grains Immature grains Damaged grains

Milled rice characteristics Physical characteristics • Milling degree • Whiteness • Translucency • Grain length • Foreign material • Head rice • Chalkiness Chemical characteristics • Amylose content • Gelatinization temperature • Gel consistency

Milling Degree • Amount of bran removed in milling process • Measured by whiteness meter or amount in weight of bran removed

Whiteness A combination of • Varietal physical characteristics • Post harvest management and • Degree of milling.

Head rice • The amount of whole kernels after milling • A whole kernel is 75% +

Chalkiness • Endosperm opacity or white belly • Opaqueness has an overall chalky texture caused by interruption of final filling of the grain. • Loosely packed starch cells

Grain length • Length to width ratio stable varietal property • Japonica-short and bold • Indicia long and slender

Foreign matter content • Purity is related to the presence of dockage in the grain. • Dockage refers to material other than paddy and includes chaff, stones, weed seeds, soil, rice straw, stalks

Milled Rice Standards (Philippines) Grade Specifications GRADE Premium Grade 1 Grade 2 Grade 3 Head rice (min %) 95. 00 80. 00 65. 00 50. 00 Brokens (max %) 4. 90 19. 75 34. 50 49. 00 Brewers (max %) 0. 10 0. 25 0. 50 1. 00 Defectives: · Damaged grains, max % · Discolored grains, max % · Chalky and immature grains, max % · Red grains, max % · Red streaked grains, max % Foreign matter (max 5) Paddy (max no. /kg) Moisture content (max %) 0 0. 50 2. 00 0 1. 00 0 1 14. 00 0. 25 2. 00 5. 00 0. 25 3. 00 0. 10 8 14. 00 0. 50 4. 00 10. 00 0. 50 5. 00 0. 20 10 14. 00 2. 00 8. 00 15. 00 2. 00 10. 00 0. 50 15 14. 00

Chemical characteristics of milled rice Gel consistency measures the tendency of the cooked rice to harden on cooling. Gelatinization temperature determines the time required for cooking the rice High amylose content? Rice grains cook dry, are less tender, and become hard upon cooling. Low-amylose content? Rice grains cook moist and are sticky

Amylose content Classified as : • Waxy (1 -2%) • Non waxy (>2%) • Very low (2 -9%) • Low (10 -20%) • Intermediate (20 -25%) • High (25 -30%) High amylose • High volume expansion, dry and flaky during cooking, hard upon cooling

Amylose Content 25 -30% amylose content is classified as High Intermediate amylose rice is preferred in most ricegrowing areas of the world except where low amylose japonicas are grown 20 -25% amylose content is classified as Intermediate. 10 -20% amylose content is classified as Low 10% HIGH MEDIUM LOW 20% 30%

Gelantization temperature • Time required for cooking • Measured by alkali spread factor • Environment affect- higher temperature during growing high gelatinization temperature Classification: • 1 -2 high (74. 5 -80 oc), • 3, high intermediate, • 4 -5, intermediate (70 -74 o. C), 6 -7, low (<70 o. C

Gel Consistency If then Gel Cooked rice tends to be less sticky. consistency Harder gel consistency is associated is hard, with harder cooked rices and this feature is particularly evident in highamylose rice. Gel Cooked rice has a higher degree of consistency tenderness. This is a preferred is soft, characteristic Classific ation Length of gel (mm) Hard 27 -35 Medium Hard 36 -40 Medium 41 -60 Soft 61 -100

Maintaining and improving grain quality • Variety • Crop management • Post production

Variety Selection • Short and medium type grains produce higher head yield • Earlier maturing varieties produce less head rice than late maturing varieties • Uniform filling varieties have higher grain density and less chalkiness • Flower unevenly also ripen unevenly.