Structural,Functional And Rheological Properties Of Rice Dreg Protein As Impacted By Transglutaminase And Glycosylation Induced Crosslinking

The cheap by-product of rice syrup as a raw material, the alkali extraction and acid precipitation method for extracting can get a purity of more than 90% of the rice dreg protein(RDP). Transglutaminase(TG) can make small molecule form polymer, changing the structure of RDP and affect its functional properties and rheological properties; glycosylation reaction is also a way to improve the functional properties of the protein. The effect of TG in the Maillard-type glycation on the plant protein were investigated. The effects of different molecular weights sugar with cross-linked rice dreg protein in wet reaction conditions were carried out.The RDP were dispersed in deionized water(containing 4% protein, w/w). Then TG was added at an enzyme to protein substrates ratio(0, 5, 10, 20, 50 U/g protein) and incubated at 37 °C shaking for 3 h. The reaction was stopped immediately by cooling the samples to 4 °C in an ice water bath for 30 minutes and then the samples were freeze-dried for further use. The extent of TG induced cross-linked of of RDP on the structure, properties and in vitro digestibility were investigated. SDS-PAGE showed the disappeared of some small fragments and the formation of high molecular mass. With the extent of cross-linking broading, fourier transform infra red spectroscopy(FTIR) indicated that ?-sheet groups increased and ?-turn was evidently decreased, which might be concerned with the total and exposed free sulphydryl groups declined. The cross-linked protein exhibited higher surface hydrophobicity and emulsifying activity, and then declined when TG level increased to 10 U/g protein. Meanwhile, the cross-linked protein exhibited lower emulsion stability and water binding capacity, but better oil binding capacity than RDP. The solubility of the cross-linked decreased, while rheological poperties and in vitro digestibility of the RDP were gradually and significantly improved with the increasing extent of cross-linking. These results suggest that adding appropriate transglutaminase to form cross-linking in RDP could be a useful way to improve functional properties of RDP.In order to investigate the effect of TG in the Maillard-type glycation on the plant protein. In this study, RDP glycated with glucose, ribose, and maltodextrin under a mass ratio 1:1 by dry-heated Maillard reaction with / without TG(10 U/g RDP) were investigated. We studied structural Characteristics and rheological Properties of RDP-Sugars Conjugates Products as Impacted by TG. The results showed that the Maillard reaction products(MRPs) of RDP with ribose exhibited the highest degree of substitution(DS) and TG could improve DS; the ?max of the intrinsic fluorescence were red shift and their intensity decreased, and the structures of MRPs were different; while TG had little impact on the structure of MRPs. Glycosylation reaction could reduce the surface hydrophobicity; Lys and Arg were mainly reduced during the Maillard reaction, ribose was more conducive to free amino reaction. TG promoted the increase of surface hydrophobicity, while had little impact on the structure of MRPs and amino acid composition. Rheology measurement indicated that all MRPs solution were pseudoplastic fluid, the maximum apparent viscosity was ribose grafted product, and TG promoted the apparent viscosity increased. Mechanical spectra showed the dynamic shear modulus of the three kinds of MRPs varies with increasing frequency, MRPs of ribose with RDP exhibited gel-like characteristics(G' > G ") and TG improved G' and G" values of MRPs from ribose or glucose glycosylated and cross-linked RDP.In order to investigate the effect of different molecular weight sugar on plant protein in glycosylation reaction. The 10 U/g cross-linked RDP as a novel plant protein glycated with glucose/ lactose/ ribose/ gum arabic mass ratio 1 : 1 in 2% solution under wet Maillard reaction. The glysocylation reaction product prepared with cross-linked RDP with ribose showed the greatest improvement in functionality, followed by glucose, lactose and gum arabic. The DS increased during the initial 15 min and remained rather constant upon continued heating. In the rheological properties, the apparent viscosity of gum arabic and lactose in maillard reaction product obtained less than the original cross-linked RDP; the apparent viscosity of the reaction product of mono sugar is higher than the cross-linked RDP.