Effect Of Ultrasound On Structure And Antioxidant Of Maillard Products Of Whey Protein Isolate And Its Hydrolysate

Whey protein is considered to be a quality protein resource,and its widely used in food industry due to its functional properties.In recent years,it has been found that the Maillard reaction has a strong effect on the antioxidant activity of proteins and peptides,and has the characteristics of high efficiency,low toxicity and so on,therefore,it is commonly concerned in food applications.Ultrasound is a kind of new environmental-friendly processing technology,and it may change the properties of raw materials because its unique hole effect can produce tremendous pressure,shear force.At present,the application of ultrasound in the Maillard reaction system is mainly focused on the reaction between protein and reducing sugar.However,the study on the effect of ultrasound on the Maillard reaction system of protein hydrolysates and reducing sugars has been few reported.In this experiment,the Maillard reaction between whey protein isolate(WPI)and its hydrolysate(WPH)and galactose(Ga)was studied under the condition of ultrasound assisted water bath heating.And the process of the Maillard reaction,the structure and antioxidant activity of Maillard reaction products have been studied.The research contents and results are as follows:(1).Different times(0,1,2,3,4,5 h)of hydrolysis of whey protein hydrolysates and different sugars(glucose,galactose,lactose,dextran,isomaltooligosaccharide)were reacted to identify the particular time and the type of sugar by reduing power.The results showed that the reducing power of the Maillard reaction products reached the maximum 0.63 when the hydrolysis time of whey protein hydrolysate was 3 h,and the reducing sugar was galactose.The following hydrolysis time and the types of reducing sugar were determined by this.(2).The effects of ultrasound time and ultrasound power on the process of the Maillard reaction were studied by analyzing the browning intensity,the intermediate products,the degree of grafting and the fluorescence spectrum.The results showed that the browning intensity of WPI-Ga and WPH-Ga reached the minimum of 0.24 and 0.29,respectively non-ultrasound,intermediate products of WPI-Ga and WPH-Ga reached maximum when ultrasound 60 min and non-ultrasound,respectively,and the values were 1.37 and 1.08.When the time of ultrasound was 60 min,the crest vlaue of intermediate products were 1.37 and 1.10 when ultrasound 200 W and 100 W.The degreeof grafting of WPI-Ga reached the maximum of 20.89% when ultrasound 30 min,which was significantly higher than that of the non-ultrasound group(P<0.05).However,the degree of grafting of WPH-Ga non-ultrasound reached the maximum of 21.80%.The influence of ultrasound power on the degree of grafting is more complex.The degree of grafting in both groups was the highest in the absence of ultrasound.The results of fluorescence spectra showed that the appropriate ultrasound treatment could promote the formation of the Maillard reaction products of WPI-Ga and WPH-Ga.Therefore,appropriate ultrasound treatment could promote the process of the Maillard reaction.(3).The effects of ultrasound treatment on the structure of the Maillard reaction products of WPI-Ga and WPH-Ga were studied by analyzing the intrinsic fluorescence spectra,UV spectra and fourier transform infrared spectroscopy.The intrinsic fluorescence spectra showed that the maximum emission wavelength of WPI-Ga and WPH-Ga would be red shifted with the increase of ultrasound time and ultrasound power,which indicated that ultrasound could make the structure of Maillard reaction products loose.UV absorption spectra showed that the maximum absorption peaks of WPI-Ga and WPH-Ga products with ultrasound were significantly higher than those wihtout ultrasound,indicating that the hydrophobic residues were exposed gradually,and the corresponding UV absorption values increased.IR spectra showed that the structure of WPI and its hydrolysates were changed by the attachment of sugar to them.Meanwhile,the second level structure of the Maillard reaction products could be changed through ultrasound.Therefore,ultrasound treatment could affect the structure of the Maillard reaction products.(4).Through the determination of the reducing power,ABTS+ radical scavenging ability,DPPH radical scavenging activity,hydroxyl radical scavenging ability,and inhibition of lipid peroxidation,we analyzed the effect of ultrasound time and ultrasound power on the antioxidant activity of the Maillard reaction products.The results showed that the reducing power of both groups of the products of WPI-Ga and WPH-Ga reached the maximum of 0.481 and 0.699 when ultrasound was 200 W and 60 min,which were significantly higher than those of the non-treated group(0.419,0.622)(P<0.05).The ABTS+ radical scavenging ability of WPI-Ga and WPH-Ga products reached the maximum of 44.85% and 51.71% in the ultrasound 200 W,60 min,which was significantly higher than that of the control group(38.97%,43.16%)(P<0.05).The DPPH radical scavenging ability of WPI-Ga and WPH-Ga products reached the maximum of 54.89% and83.83% when the ultrasound power was 200 W,which was significantly higher than that without ultrasound(49.95%,73.24%)(P<0.05).The DPPH radical scavenging ability of both group reached the maximum of 54.56% and 81.08% when the ultrasound time was 60 min.The hydroxyl radical scavenging capacity of WPI-Ga and WPH-Ga products was the strongest at 93.05% and93.39% when the ultrasound time was 60 min,which was significantly higher than that without ultrasound(85.70%,86.44%)(P<0.05).The hydroxyl radical scavenging capacity of WPH-Ga products reached the maximum of 94.59% and 96.47% at 400 W when the ultrasound time was fixed.The inhibition of lipid peroxidation of WPI-Ga and WPH-Ga products reached themaximum of 56.59% and 63.71%,which was significantly higher than that without ultrasound(61.15% and45.96%)(P<0.05).With the increase of ultrasound power,the inhibition of lipid peroxidation of WPI-Ga was the largest at 51.48% when the ultrasound power was 200 W,but that of WPH-Ga was the largest at 65.63%% when the power was 400 W.In addition,except for hydroxyl radical scavenging ability,other antioxidant indexes of WPH-Ga products were significantly higher than those of WPI-Ga products(P<0.05).Therefore,the appropriate ultrasound treatment might improve the antioxidant capacity of the Maillard reaction products.Compared with common antioxidants of VC(Vitamin C,0.1mg/m L)and BHA(butyl hydroxy anisole,0.1mg/m L),the reduction ability and hydroxyl radical scavenging capacity of WPI-Ga and WPH-Ga products were higher than those of Vc and BHA with ultrasound of 200 W,60 min(P<0.05).ABTS+ radical scavenging capacity was significantly higher than Vc(P<0.05),but lower than BHA(P < 0.05).DPPH radical scavenging capacity of VC was the strongest,followed by WPH-Ga products,BHA and WPI-Ga products.The inhibition of lipid peroxidation of BHA was the strongest,followed by WPH-Ga products.In general,the WPI-Ga and WPH-Ga products showed better antioxidant ability,and the ultrasound treatment groups were higher than that without ultrasound.