Studies On The Thermal Stability Of Barley Protein By Maillard Reaction

Brewing barley is the most important raw materials in beer production. The protein in thebarley plays an important part in the quality of malt and beer, and the heat-stable protein playsimportant roles on formation and stability of the beer foam. It was reported that the functionalproperties of protein could be modified by Maillard reaction. The effect of the thermalstability of barley protein by Maillard reaction was studied in this thesis in order to study theHeat-resistant mechanism of barley protein in theory. Paper provide a theoretical reference tomodified proteins and have a good academic significance.The effects of glycation reaction on the thermal stability of barley protein were discussed indetail. Covalent compounds in heat resistance as an index, through the sugar screening todetermine the glucose as sugar-based donor during the Maillard reaction. The improvement ofthermal stability of the conjugates combined with graft degree, browning, pH value of thesystem were studied in order to optimize the reaction conditions. Single-factor experimentshown that barley protein reacted with glucose (WR=1:1) at pH9.0,90℃water bath for40min has excellent functional properties. The graft degree of the Pr-G was23.5%.We have analysed the stability change of four kinds of proteins (water-soluble proteins,salt-soluble proteins, hordeins and alkali-soluble proteins) of barley towards heat (95～125℃) and direct investigated four kinds of proteins of barley glycated by Maillard reactionstoward heating. Sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE)patterns indicate that glycated proteins (water-soluble proteins-glucose and salt-solubleproteins-glucose) exhibited higher thermal stability than the native proteins towards a widetemperature conditions.It was also found that major component of proteins was a molecularmass of40kDa exhibited a lower thermal stability at120℃than nonspecific lipid transferprotein1(LTP1).The structure of the Pr-G conjugates were analyzed by florescence analysis, FTIR,SDS-PAGE, DSC and amino acid analysis. The conjugates have the strongest florescenceintensity when emission was347nm and the excitation was425nm. The result ensured that the Maillard reaction was happened．The FTIR analysis of the sample showed the sameconclusion that glucose was grafted to barley protein by covalent band. According to theanalysis of SDS-PAGE，the new bands of the grafts subunits were closer to the upper ofseparating gel, Subunit protein molecules undergo some changes. Thermal denaturationtemperature DSC analysis shows that the structure and composition of the graft may havequite different before and after. The amino acid analysis shown that the content of Cysteine,Lysine, Proline and Arginine was decreased by glycation.