Transglutaminase treatment of brown rice flour: A chromatographic, electrophoretic and spectroscopic study of protein modifications |
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Authors: | Stefano Renzetti Juergen BehrRudi F Vogel Alberto BarbiroliStefania Iametti Francesco BonomiElke K Arendt |
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Affiliation: | a Department of Food Science, Food Technology and Nutrition, National University of Ireland, Cork, Ireland b Biotransfer Unit, University College Cork, Ireland c TU-München, Lehrstuhl für Technische Mikrobiologie, D-85350 Freising, Germany d Dipartimento di Scienze Molecolari Agroalimentari, Università degli Studi di Milano, Italy |
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Abstract: | Recently, it was shown that transglutaminase (TGase) treatment of brown rice (BR) flour results in textural improvements of gluten-free bread. In this study, changes in the protein profiles of BR flour and protein fractions induced by TGase treatment were investigated to better understand the activity and specificity of the enzyme. Size-exclusion HPLC (SE-HPLC) profiles of flour extracts, under reducing conditions, revealed the presence of macromolecular protein complexes, as well as low molecular weight proteins. After TGase treatments (10 U/g of proteins) a general reduction in peak intensities indicated the polymerisation of BR proteins into larger, insoluble complexes. Microchip capillary electrophoresis and two-dimensional (2D) gel electrophoresis revealed that the α and β glutelin subunits were primary substrates for the polymerisation reaction, whereas albumins and globulins were only slightly affected. SE-HPLC of the protein fractions revealed glutelins’ polymerisation into high molecular weight structures after TGase treatment. Dynamic light scattering measurements showed that new supramolecular aggregates of glutelins co-existed with the macromolecular complexes already present in the untreated fraction. Front-face fluorescence approaches indicated that TGase treatment caused a decrease in protein surface hydrophobicity of BR flour, but not of the glutelin suspensions. It is concluded that the large protein complexes resulting from glutelin polymerisation and the stronger hydrophobic interactions among proteins result in the improved textural properties of TGase-treated BR bread. |
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Keywords: | ANS 1 8 anilinonaphthalene sulfonate sodium salt BR brown rice DLS dynamic light scattering Fmax surface hydrophobicity HMW high molecular weight Kd apparent dissociation constant LMW low molecular weight MCE microchip capillary electrophoresis MW molecular weight SE-HPLC size exclusion-HPLC TGase transglutaminase SDS-PAGE SDS-polyacrylamide gel electrophoresis |
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