The Saccharide Graft Modification Of Rapeseed Protein Isolated And Its Functional Properties, Construction, Digestion And Absorption Characteristics

In this paper, the rapeseed protein isolated(RPI) and saccharides were used as the main materials to prepare the RPI-saccharide conjugates with the wet heating and ultrasound-assisted wet heating methods. The conjugates characteristics of function,construction, digestion and absorption were studied. It is expected to provide theoretical and technical basis for proper controll of the degree of protein greafting reaction in industrial scale production.Firstly, the reaction conditions of the wet heating, ultrasound-assisted wet heating and the type of reducing sugar were studied. The effects of reaction time, the ratio of RPI and reducing sugar, reaction temperature, pH and ultrasonic frequency on degree of graft(DG) have been analyzed in single factor experiments to obtain suitable conditions. The results showed that dextran than glucose is more easilier conjugate with RPI both in wet heating and ultrasound-assisted wet heating methods.The optimum conditions for wet heating graft reaction were as follows: reaction time3 h, the ratio of RPI and dextran 1:1, reaction temperature 90℃, pH 10. Meanwhile,the optimum conditions for ultrasound-assisted wet heating graft reaction were as follows: ultrasonic time 60 min, ultrasonic frequency 28 kHz, the ratio of RPI and dextran 1:1, reaction temperature 90℃, pH 10.The RPI-dextran conjugates with different DG were prepared. The effects of different DG on the physicochemical properties and structure of the conjugates were investigated. Compared with the RPI, the solubility, thermal stability, emulsifying properties of the RPI-dextran conjugates were improved significantly, and increased with DG rising. Surface hydrophobicity of conjugates decreased with the DG rising.Amino acid analysis showed that when RPI was grafted with dextran, the contents of lysine, cysteine and arginine decreased with the increasing of DG. According to the analysis of SDS-PAGE, the 7S subunit of RPI engaged in the grafting reaction, and12 S and 2S also participate in a small amount. By the analysis of HPLC, the contents of high molecular weight RPI-dextran conjugates were increased with the rising of DG, especially at low DG. It was proved by FTIR that the grafting reaction couldcause the strong vibration of the C-O bond in RPI, and RPI molecules were grafted with the dextran molecules by the covalent bond. In addition, the number of hydroxyl groups increased in the protein molecule. CD spectra showed that the α-helix decreased, while random coil increased after grafting. The structure of the conjugates displayed more flexibility. It was observed by SEM that the surface structure of the RPI-dextran conjugates was different with the native RPI. It became looser with the increasing of DG with wet heating grafting. Meanwhile, the surface structure of RPI-dextran conjugates have honeycomb structure with the increasing of DG with ultrasound-assisted wet heating grafting.The in vitro digestion and absorption characteristics of the conjugates were studied in this paper. It showed that the digestion and hydrolysis of RPI and RPI-dextran conjugates were mainly in the tryptic hydrolysis stage, and the ability of digestion characteristic decreased with increasing of DG. However the hydrolysis performance was a little affected by the DG. At the same DG, the RPI-dextran conjugates by ultrasound-assisted wet heating method are difficultly to be digested,but easily to be hydrolyzed compared with the conjugates by wet heating method.After the pepsin digestion stage, the RPI and RPI-dextran conjugates molecular weight between 110 kDa and 85 kDa were digested completely. The digestibility of RPI-dextran conjugates whose molecular weight is more than 6.4 kDa decreased with the increasing of DG. After the tryptic digestion stage, the RPI and RPI-dextran conjugates whose molecular weight between 85 kDa and 70 kDa were digested completely.The in vitro absorption characteristics of the conjugates analysis showed that the concentration of peptides in RPI and RPI-dextran conjugate’s absorption samples were 2 to 3 times than digestive samples, and increased with the increasing of DG with wet heating grafting, but decreased with the increasing of DG with ultrasound-assisted wet heating grafting. The absorption in vitro of RPI-dextran conjugates displayed no significant difference with RPI. Combined with the results of in vitro digestion analysis, the digestibility of RPI decreased slightly after grafting,but has no effect on the in vitro absorption of digestion products.