Study On Structure And Properties Of Maillard Reaction Products Of Yak Casein-Glucose

Yak casein is a unique resource of the Qinghai-Tibet Plateau.Its primary product is called Qu-La,which is made by the herdsmen in Tibetan areas.It is one of the main raw materials for industrial casein products in China.In order to improve the functional properties of yak casein and expand its application scope,this study chose glucose to modify Yak casein by wet method glycosylation.The structure and functional properties of glycosylated casein were studied systematically,and compared to Holstein casein.The glycosylation conditions were p H 9.0,reaction temperature 100°C,and reaction time 3h.The results of the study are as follows:?1?As the glucose concentration increases,the pH of the Yak casein-glucose system decreases;the content of intermediate increases dramatically at 0.5:1?glucose:casein,g/g?,then increases slightly,decreased afterwards;the browning intensity showed a slight change;the fluorescence of Maillard reaction products reached its maximum at 1.5:1,then decreased;the free amino group content decreased significantly except for 2.5:1.?2?With glycosylation under different concentration glucose for Yak casein,UV absorption spectra of the products were in the order of 2.5:1,2:1,1:1,1.5:1,0.5:1,0:1according to the maximum absorbance.As to the FTIR spectra of glycosylated Yak casein,the absorbance of the C-OH vibration was found in the range of 950-1170cm^-1,and-NH₂bending vibration weakened under 1560cm^-1.C-N bending vibration of those increased at1080cm^-1.Compared with the control group which was heated without sugar,the irregular content of secondary structure decreased and the turn content increased except for 1.5:1.The the maximum intrinsic fluorescence intensity of glycosylated Yak casein decreased.The maximum emission wavelength increased gradually with the increase of glucose concentration<2:1,then decreased.The intensity of ANS fluorescence decreased significantly.The maximum emission wavelength of ANS fluorescence increased.The surface hydrophobicity index of Yak casein-glucose system model decreased as the glucose concentration increased.?3?The emulsifying activity,10min and 30min emulsion stability of Yak casein-glucose Maillard reaction products reached the maximum values at 2:1,which were 16.745m²/g,46.271%and 42.421%respectively.Foaming capacity and foam stability at 5min,10min and30min of those reached the maximum values at 2:1,which were 168.222%,98.218%,97.293%,and 94.458%,respectively.Glycosylation reduced the soluble nitrogen content and white color of Yak casin-glucose system,but its oil absorption increased.With the increase of glycosylation degree,the digestibility of the products decreased.The oil absorption of the products increased and reached the maximum at 2:1,then decreased.?4?The reducing power of Yak casein-glucose Maillard reaction products increases with the increase of its concentration.When its concentration is higher than 4mg/mL,the higher the sugar ratio,the stronger the reducing power of at the same concentration.The DPPH free radical scavenging activity of the products at each concentrations increased significantly at0.5:1,which reached the maximum at 1.5:1 at different concentrations.When the concentration of the products was 1mg/ml,Fe²⁺chelating capacity of each group slightly increased.The lipid peroxidation inhibition ability of those increased with the increase of its concentration.In summary,the glycosylation modification improves the functional properties and antioxidant activity of Yak casein.Therefore,the industrial application of Yak casein could be expanded by glycosylation through Maillard reaction.