Optimization Of Maillard Reaction Conditions For Chicken Liver Protein Enzymatic Hydrolysate And Its Product Characteristics

Chicken liver is a large yield of by-product in poultry with low utilization rate and highprotein content(more than 20%).However,it is difficult for consumers to accept because of its special smell.Therefore,except a small amount of chicken livers are eaten fresh and deep processing,most of them are simply processed into animal feed and cannot be deeply developed,which not only wastes precious resources but also pollutes the environment.In response to the above problems,chicken liver was taken as the research object to modify chicken liver protein and optimize Maillard reaction(MR)conditions.Meanwhile,the structure and properties of Maillard reaction products(MRPs),formation mechanism of flavor substances and changes in biological activity were explored.This study provided theoretical basis and practical guidance for high-value utilization of chicken liver and its application in food processing and pet food.The details are as follows:(1)Optimization of MR conditions for chicken liver hydrolysatesIn order to study the optimal reaction condition between chicken liver protein hydrolysate and reducing sugar,we studied the effect of chicken liver protein hydrolysis degree(DH),reducing sugar species,reaction p H,reaction time,and reaction temperature on the MR process,respectively.Through single factor and response surface optimization tests,taking the absorbance of browning degree and intermediate products of the products as indexes,the optimal reaction conditions were obtained as follows:reaction temperature 138.78?,initial p H 7.99,reaction time 93.14 min.In these conditions,the browning degree of the product was 2.091.Three times verifications test showed the browning degree of the obtained reaction product is 2.104,which had 99.35%coincidence degree.The browning degree of MRPs of chicken liver protein was 0.170 under the same conditions.Therefore,the degree of reaction between chicken liver protein hydrolysate and xylose increased significantly.(2)Effect of MR on properties of chicken liver protein hydrolysateIn this part,the color,particle size,fluorescence spectrum,differential scanning calorimetry(DSC)of the products before and after the MR were measured to analysis the changes of characteristics.The results indicated that the color and particle size of the chicken liver protein MRPs(CLPM)and the chicken liver protein hydrolysate MRPs(CLPHM)were significantly increased(P<0.05),and the fluorescence intensity and thermal stability were significantly increased(P<0.05).(3)Effect of MR on structure of chicken liver protein hydrolysateIn this part,size exclusion chromatography-high performance liquid chromatography(SEC-HPLC),ultraviolet spectrum scanning,endogenous fluorescence spectrum,X-ray diffraction(XRD)and Fourier transform infrared spectroscopy(FT-IR)of the products before and after the MR were measured to analysis changes of the structure.The results indicated that the molecular weight of the CLPHM(<1.35 KDa)was higher than that of the CLPM,and the molecular weight in 1.35?17 KDa was lower than that of the CLPM.The results of ultraviolet spectrum and endogenous fluorescence spectrum showed that the structure of the CLPHM has been changed,and the tertiary conformation of the product became loose.The FT-IR and the XRD showed that the secondary structure of the products had been changed.Therefore,proteolytic treatment will have a certain effect on the structure of the MRPs.(4)Effects of MR on volatile flavor compounds of the CLPHIn this section,in order to investigate the effect of MR of the CLPH on the volatile flavor substances,the volatile flavor substances,taste and amino acid components of the products before and after MR were determined.The results showed that a total of 86 volatile flavor compounds were identified,including 21 aldehydes,17 alcohols,7 esters,9 ketones,16alkenes and 16 other compounds.The volatile compounds with higher proportion in the CLPM and the CLPHM were aldehydes and ketones.The proportion of olefins and alcohols in the CLP and the CLPH were higher.The bitterness and salty taste of the CLPHM decreased significantly,and the delicate flavor also decreased.The loss rate of hydrolyzed amino acids of the CLPHM is as high as 57.36%and the loss rate of free amino acids is as high as 79.33%.Therefore,the CLPHM was able to produce more flavor substances and enrich aroma.(5)Effects of MR on biological activities of the CLPHIn this section,in order to investigate the effect of MR of the CLPH on their biological activities,the antioxidant and antibacterial activity of the products were measured.The result of antioxidant activity of the MRPs showed that the reducing power of the CLPHM was significantly higher than the CLPM(P<0.05).When the concentration of the products was 0.5 mol/m L,the CLPHM was effective against hydroxyl radicals,DPPH·free radicals and ABTS~+free radicals were 55.3%,85.5%,and 94.68%respectively,which were significantly higher than those of the CLPM(P<0.05).This indicated that the MR could increase the antioxidant activity of the products.For the antibacterial activity of the MRPs,the results showed that the CLPHM could effectively inhibit the growth of S.saprophyticus,while its inhibitory effect on E.coli was weaker.Therefore,it showed that MR could increase the antibacterial activity of the chicken liver protein.(6)Effects of MR on the pet palatability experiments of the CLPHBased on the above researches on the color,properties,and flavors of MRP,in order to verify the application of the CLPHM in the actual food of pet dog,the pet palatability experiments(first bite preference test and two bowls test)of the MRPs were performed.The results showed that the dog food sprayed with 3%the MRPs,the first mouth test and the two bowl test of the CLPHM were significantly higher than those of the control group(CLPM)(P<0.05).Therefore,the palatability of the MRPs could effectively improve by proteolytic hydrolysis,and it promoted the color and flavor of the MRPs.