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Protein Analysis in Some Selected Rice Varieties of Bangladesh

FATEMA BEGUM
Grain Quality and Nutrition Division, Bangladesh Rice Research Institute, Gazipur-1701, Bangladesh.

N. H. CHOWDHURY
Grain Quality and Nutrition Division, Bangladesh Rice Research Institute, Gazipur-1701, Bangladesh.

Abstract/ Executive Summary:

Four varieties of rice including two locally improved (Rajasail and Habiganj IV), one high yielcling (BR3) and one glutinous (Binni) rice were analyzed for protein by Micro Kjeldahl and SDS-PAGE analysis. The protein content varied from 5.5 - 7.3% with an average protein level of 6.0% (± 0.87). Protein content of glutinous rice (Binni) was not significantly different from non-glutinous rice BR3 and Rajasail. Prolamin fraction of Binni and Rajasail were similar. BR3 was low in prolamin and Binni was low in albumin and glutelin. Rajasail was rich in globulin and prolamin. 50S-PAGE and densitometer traces obtained for albumin, globulin, prolamin and glutelin fractions showed them to be different. A high molecular weight protein band (MW above 26,000 daltons representing globulin fraction was missing in Habiganj IV and Rajasail varieties. On the other hand a protein band (MW above 15,000 daltons) representing albumin fraction was absent in Rajasail and Binni varieties.

Keywords: Protein analysis, Rice

Location: Bangladesh Rice Research Institute, Gazipur-1701, Bangladesh.

Start Date:

End Date:

Program Area: Quality and Nutrition

Commodity: Rice

Objectives:

To estimate and fractionate the protein of some selected rice varieties of Bangladesh.

Methodology:

Four rice samples BR3, Habiganj IV, Rajasail and Binni were collected from the Bangladesh Rice Research Institute, Joydebpur. Among them Binni is glutinous and others are nonglutinous. The rough rice was dehulled by Satake Rice Mill. The resulting brown rice was polished for 45 second in a Satake Grain Testing mill TM 05. This polished rice was ground by a Hammer mill, (mill size 8"). Fine powder was collected by 250 μm seived and powder was used for fractionation of protein. Rice powder (10 g) was taken in 50 ml of 0.5 M NaCl solution under mild stirring for two hours. The suspension was centrifuged for 25 minutes using a Beckman J2HS high speed 17 centrifuge. The supernatants was decanted and the extraction process was repeated twice. The pooled supernatants were dialyscd against distilled water for 20 hours. The dialyzed sample was centrifuged to separate globulin (salt soluble protein) from supernatant albumin (water soluble protein). The residue was then washed out with distilled water to remove salt. Prolamin was extracted after removal of albumin and globulin from rice flour. The extraction process of prolamin was the same as albumin and globulin excepting that 70% ethanol was used instead of NaCI. Glutelin fraction was extracted from residue (after removal of albumin, globulin, prolamin) by NaOH (0.1 M). The NaOH soluble fraction was dialyzed against distilled water to remove alkali. The four soluble fractions (albumin, globulin, prolamin and glutelin) were freeze dried. The final residue was dried in an oven for 20 hours at 100?. The protein fractions were used to determine the composition of protein by SDS Gel electrophoresis. SDS-PAGE was performed according to the method of Laernmli on a slab gel of 7.5-18% acrylamide. The electrophoresis was run in a 0.15 ern thick gel. Bovine albumin, (MW 66,000 daltons), egg albumin (MW 45,000 daltons), glyceroldehyde 3-P dehydrogenase (MW 36,000 daltons); bovine carbonic anhydrase (MW 29,000 daltons); trypsinogen (bovine pancreas) (MW 24,000 daltons); soybean trypsin inhibitor (MW 20,000 daltons); alfa- lactalbumin (bovine milk) (MW 14,200 daltons) were used as protein standard. The gel was stained with coomasie brilliant blue R-250 and then destained with methanol until the gel background was clear for photography. The molecular weight of the different fractions were calculated from calibration curves (MW plotted versus the distance migrated). The relative amount of protein in each SDS-PAGE protein band was determined by a densitometer traces. Nitrogen content was estimated by Micro Kjeldahl method and per cent of protein was calculated from per cent of nitrogen multiplied by 5.95. This factor is based on the nitrogen content (16.8%) of the major rice protein glutelin.

Source of Information: Journal of The Asiatic Society of Bangladesh Science. Vol. 23, (No-1), pp: 87-94, June-1997

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Achievement/Findings:

Protein content was higher in Habiganj IV. Other three varities BR3, Rajasail and Binni had low but similar content. This showed that low amylose content as in glutinous Binni variety had no effect on protein content. The banding pattern of individual protein fractions of different rice varieties showed substantial difference in their sizes ranging from low to high molecular weight polypeptides. The albumin and glutelin fraction of binni variety were low. High MW protein was missing in globulin fraction of Rajasail and Habiganj IV varieties. Low MW protein was missing in glutelin fraction of BR3. Per cent of protein and MW of prolamin in Rajasail was close to BR3. Thus this study revealed some significant differences between the protein fractions of four cultivars of rice. The variation of molecular size within a fraction varies from variety to variety indicating that this variation is genetically controlled. These information will be useful for the development of new variety of rice with improved protein quality.

Knowledge Management: Journal