| At this stage,the frozen dough has developed rapidly in China due to its safety and convenience.Gluten was also an important part of the dough.Studies have shown that the migration of gluten protein during the freezing period causes the occurrence of ice crystal growth and recrystallization,which causes the quality of gluten protein during the frozen storage to deteriorate,which seriously affects the food quality and commercial value of frozen dough products,which limits its a wider range of applications.The addition of Poly-γ-glutamicacid can significantly inhibit the moisture migration of gluten protein during freezing,improve its protein network structure,and effectively improve its freezing stability.In this paper,the effects of Poly-γ-glutamicacid on hydration,structure,rheological properties and freezing stability of gluten protein were studied by using rotational rheometer(DHR),nuclear magnetic resonance(NMR),and fourier transform infrared(FITR),scanning electron microscope(SEM),thermogravimetric analyzer(TGA),differential scanning calorimeter(DSC),etc.Through the study on the stability of glutenin freezing and the stability of gliadin freezing,the mechanism of Poly-γ-glutamic acid affecting the stability of gluten protein frozen storage was explored.The main conclusions are as follows:(1)The addition of γ-PGA significantly increased the water retention of gluten protein,improved the viscous properties of gluten protein,and reduced the elastic properties of gluten protein.When 1%γ-PGA was added,the bound water content in gluten protein increased significantly by 3.2%,and the free water content decreased from 4.27%to 0.86%.Microstructural observations indicate that the addition of γ-PGA results in a more uniform,finer pore size protein network structure for gluten protein.This indicates that γ-PGA binds the area protein to water more tightly,improves the three-dimensional network structure of gluten protein,changes rheological properties and enhances its water retention capacity,thereby changing the functional properties of gluten protein.(2)The addition of 1%γ-PGA significantly reduced the conversion of weakly bound water to free water during gluten during freezing,inhibiting the decrease of α-helix and the increase of random curl in the secondary structure of gluten.It indicates that the orderedto-disorder conversion caused by the freezing was effectively suppressed.Moreover,the addition of γ-PGA has the effect of protecting the three-dimensional network structure of the protein,so that the gluten protein can maintain a continuous network structure after being frozen.Thereby,the thermodynamic properties of gluten and the decrease of viscoelasticity were improved,and the freezing stability of gluten protein was improved.(3)The addition of γ-PGA to glutenin causes partial free water to be converted to weakly bound water,and the tendency of free water to increase during freezing was suppressed,while suppressing the rise of irregular curl in the secondary structure of the protein.Through observation of the microstructure,it was found that 1%γ-PGA slightly increased the glutenin pores in the early stage of frozen storage,and still maintained a good network structure.Although it was difficult to avoid agglomeration in the late frozen period,γ-PGA maintains the glutenin continuity consistently,thus effectively protecting the thermodynamic properties of glutenin.It was also found that γ-PGA effectively improved the reduction of glutenin elastic properties,but had no significant effect on viscous properties.(4)NMR showed that the weakly bound water of gliadin during the freezing period was transformed into the bound water,and the thermal denaturation temperature decreased obviously,and the structure damage was significant.The addition of γ-PGA improved the water migration during the storage of gliadin,and inhibited the decline of protein denaturation temperature and denaturation enthalpy.It shows that the stability of the frozen reservoir was improved and the structural retention was better in the microstructure. |
