Extractability and chromatographic separation of rice endosperm proteins |
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| Institution: | 1. K.U. Leuven, Laboratory of Food Chemistry, Kasteelpark Arenberg 20, 3001 Leuven, Belgium;2. Remy Industries N.V., Remylaan 4, 3018 Wijgmaal, Belgium;1. Program of Food Technology, School of Agro-Industry, Mae Fah Luang University, Chiang Rai 57100, Thailand;2. Institute of Food Technology, Department of Food Science and Technology, BOKU - University of Natural Resources and Life Sciences, Vienna, Austria;1. College of Agronomy, Nanjing Agricultural University, Nanjing 210095, PR China;2. Jiangsu Collaborative Innovation Center for Modern Crop Production, Nanjing 210095, PR China;1. Key Laboratory of Carbohydrate Chemistry and Biotechnology Ministry of Education, Jiangnan University, Lihu Road 1800, Wuxi 214122, China;2. National Engineering Laboratory for Cereal Fermentation Technology, School of Food Science and Technology, Jiangnan University, Lihu Road 1800, Wuxi 214122, China;3. Jiangsu Provincial Research Center for Bioactive Product Processing Technology, Jiangnan University, Lihu Road 1800, Wuxi 214122, China;1. State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi 214122, China;2. School of Food Science and Technology, Jiangnan University, Wuxi 214122, China;3. National Engineering Research Center for Functional Food, Jiangnan University, Wuxi 214122, China;1. School of Food and Biological Engineering, Hefei University of Technology, 193 Tunxi Road, Hefei, Anhui 230009, PR China;2. Engineering Research Center for Agricultural Products Bioprocessing, Ministry of Education, Hefei University of Technology, Hefei, Anhui 230009, PR China |
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| Abstract: | The molecular weight (MW) distribution of proteins extracted with different solvents from defatted rice endosperm was examined by size exclusion-high performance liquid chromatography (SE-HPLC) with 2.0% sodium dodecyl sulfate (SDS) (w/v) as mobile phase. The resulting protein peaks were further characterized by SDS-PAGE. Under the experimental conditions, 2.0% SDS extracted 64% of the proteins. Adding 6.0 M urea resulted in a 15% increase in extractability (up to 79%). With using 20–100 mM NaOH, 70–81% of the proteins were extractable. Maximum extractability was reached with 2.0% SDS, 6.0 M urea and 0.5–1.5% dithiothreitol (DTT). Apparent MW profiles of rice endosperm proteins allowed classification into six fractions of decreasing apparent MW. Fraction VI contained the low MW albumin, globulin, and prolamin protein material. Fractions IV and V originated from α and β glutelin subunits, respectively. The polypeptides of fraction III consisted of an α and a β subunit linked by an intermolecular disulfide bond. The polypeptides of fractions I and II were dimers, trimers or more highly polymerized forms of the (α–β) glutelin subunit dimer in fraction III. While the work confirmed that rice glutelin is composed of polymers of α and β subunits, remarkably, higher MW glutelin aggregates (fractions I–III) only partly dissociated on reduction. Low MW protein material (fraction VI) was entrapped in the aggregated protein network and was released on reduction. The rapid and reproducible SE-HPLC method developed for rice protein separation allows a more quantitative approach than SDS-PAGE. |
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