Study On The Factors Affecting Interaction Between Soy Protein Isolate And Fruit Flavor Compounds

Soybean protein isolate(SPI)has superior amino acid balance and ascendant functional properties,which are important protein resource and important ingredient resource in food industry.Due to that the flavor compounds of soy protein and juice/yogurt are difficult to fusion and protein selective adsorption and release of flavors,it exists flavors of containing soy protein food deterioration problems more or less,and result to consumers difficult to accept.flavor deterioration problems is difficult to solve so far even add essence,that make it harder for soybean protein to used in the beverage of high value-added system,candy and other processed foods.The problem is mainly due to the interaction between SPI and flavor compounds,which is less study,the data analysis model is controversial.The conformation changes of SPI during processing,solution pH change,the different structural homologue flavor compounds under the condition of coexistence,adding food ingredients of SPI and interaction effect of flavor compounds is lacking,leading to flavor systems containing soy protein improving ways was lack of technology.Based on this,this study is aimed the system interaction between typical flavor compounds of fruits and SPI,with fruit flavors with SPI incompatibilities as the breakthrough point,aiming at the typical fruit flavor compounds of small molecules.First of all,research method,the analysis model and flavor compounds the influence of the concentration of SPI interact with flavor compounds was studied;On this basis,the influence of SPI structure change on the interaction between SPI and flavor compounds in aqueous solution,the influence of solution pH value on the interaction between SPI and flavor compounds were studied.Finally,the main components of pear flavors were taken as the research object to explore the interaction between various flavor compounds and SPI while they coexisted,so as to provide a basis for regulating the flavor of food systems containing SPI in the future.Firstly,the influences of two methods of SPME and SH technologies,as well as two data analysis models of Klotz and Hill on the interaction between SPI and flavor compounds were compared and studied after SPI was mixed with different concentrations of flavor compounds.Flavors of citronellate propionate,citronellate acetate,citronellol,α-pinene and terpinene were selected.The concentration of flavor compounds was in the range of 0.04-0.16 m M in low concentration system and 0.4-1.6 m M in high concentration system.After the interaction parameters were obtained,fluorescence spectrum,Zeta potential(ξ),particle size and surface hydrophobicity were used to characterize the changes of protein structure and aggregation state,which further confirmed the interaction mechanism.The results showed that while the concentration of flavor compounds citronellal,citronellate propionate,citronellate acetate and citronellol at high(0.4-1.6 m M)was suitable for the determination of the concentration by SH technique and the analysis by Hill model with a high binding energy,which can induce significant changes in the conformational changes of SPI and generate new binding sites.The order of conformational change intensity of SPI induced by four flavor compounds in water phase was: citronelaldehyde > citronella propionate > citronelloate acetate > citronellol,the binding was nonlinear.While the concentration of citronellal,citronellate propionate,citronellate acetate and citronellol was low(0.04-0.16 m M),SPME and Klotz model was suitable for the determination and analysis,the binding energy of the four flavor compounds with SPI was small,and there was no significant change in the conformation of SPI in aqueous solution(p < 0.05),the binding was linear.The interaction of α-pinene and terpinene with SPI at both high and low concentrations did not induce conformational changes of SPI(p < 0.05).SPI promoted the release of α-pinene and terpinene in aqueous solution,based on the "saltingout" effect of proteins on the solubility of non-polar gases.Based on the appropriate concentration measurement method and data analysis model,and the then focuses on soybean protein structure change influence on its interaction with flavor compounds,respectively using SPME method and the model of science at lower levels flavor compounds(0.012-0.08 m M),interaction of 4 kinds of natural SPI and 80℃,90℃ and 100℃ thermal denaturation SPI with 8 kinds of typical structure and fruit flavor compounds were discussed in detail;The effects of 10 flavor compounds mixed with SPI after heating and SPI after heating on their interaction were compared and studied.The effects of SPI on the isomerization of citral and the condensation degradation of reverse hydroxyl aldehyde were also discussed.The results showed that there were primary and secondary binding sites for hexyl acetate and heptyl acetate with natural SPI and SPI with only 7S denaturation.However,the primary binding sites of SPI would disappear when all 7S and 11 S denaturation occurred.The binding capacity of the protein to hexyl acetate and heptyl acetate is reduced by the expansion,dissociation or aggregation of part or all of the structure of SPI.The relatively large spatial structures of linalool formate,linalool acetate,geraniol and linalool only had secondary binding sites with SPI.7S denaturation can increase the number of binding sites and decrease the binding constant between SPI and these flavor compounds.However,the further degeneration of SPI resulted in the decrease of binding sites and the increase of binding constants.As the denaturation degree of SPI increased,the release promoting effect of SPI on laurene and limonene decreased,and the decrease of "salting out" was related to the dissociation and aggregation of SPI and the increase of surface hydrophobicity.The chain length of flavor compounds increased,and the binding constant of flavor compounds with SPI increased.Flexibility increased result binding sites increased;The position isomers had little effect on the binding parameters.The interaction between flavor compounds and denatured SPI was less affected by the prebinding of flavor compounds to SPI.The effect of SPI structure expansion and aggregation on the interaction between SPI and flavor compounds was much greater than the effect of flavor compounds addition order.SPI can catalyze the isomerization of geranial and neral which are two isomers of citral.Citral in SPI solution can also produce methylheptenone and acetaldehyde by condensation and degradation of reverse hydroxylal by SPI catalyzed.This isomerization and condensation and degradation of reverse hydroxylal can change the flavor of food system containing citral.The catalytic rate of alcohol-washing SPI is higher than that of natural SPI and higher than that of highly thermal denaturation SPI,suggesting that partial structure expansion is favorable for catalytic isomerization,while high aggregation is unfavorable for catalytic isomerization.In order to clarify the influence of pH changes on the interaction between SPI and flavor compounds,SPME method and Klotz model were used to investigate the interaction between SPI and flavor compounds of 8 typical fruits under pH 3,6,7 and 9 at low concentration of flavor compounds(0.012-0.08 m M).The effect of pH on SPI catalyzed condensation degradation of citral against hydroxyl aldehyde was also studied.The results showed that there were first and second binding sites between hexyl acetate and heptyl acetate and SPI at pH 6.0,7.0 and 9.0,the first binding sites disappeared when pH was changed to 3.0.While pH is shifted to 9,the binding constant of the first binding site can be greatly increased,and the total binding capacity can be greatly improved compared with the other pH conditions.There were only secondary binding sites between linalool formate,linalool acetate,geraniol,linalool and SPI with relatively higher steric hindrance.While pH shifted from 3.0 to 9.0,the binding ability of protein to linalool formate,linalool acetate,geraniol and linalool increased.The promotive release of limonene and laureene tended to decrease.pH has a significant effect on SPI catalytic degradation of reverse hydroxyl aldehyde condensation.The methyl heptenone generation rate increased as pH increased.While the pH value is lower than 6,the methyl heptenone generation rate is almost zero.On the basis of the above studies on the interaction between single flavor compounds and SPI,the interaction between SPI and various flavor compounds with different concentrations was studied by taking 15 pear flavor compounds as the object.The interaction of heptyl acetate and octyl acetate,as well as undecaldehyde and carvone,which have different structures with SPI in high and low concentrations,single presence and pair coexistence were studied.The release of limonene,laureene and undecaldehyde was investigated when they were single and when they coexisted in pairs.The effects of SPI concentration,solution pH value,SPI thermal denaturation,hydrophilic colloid and other factors on the interaction with SPI in the coexistence of 15 typical flavor compounds in pear flavor system were studied.The results showed that hexyl acetate and heptyl acetate,homologous compounds with similar structure,had competitive binding with SPI in coexistence at both low and high concentrations.Two flavor compounds with different steric hindrance and flexibility,such as undecanal and carvone,have little influence on each other’s interaction with SPI.Whether the four compounds exist singly or coexist in pairs,there is a phenomenon that the compound concentration increases and the binding force increases.These results indicated that SPI structure expansion,whether it was caused by the increase of flavor compound’s own concentration,or the SPI structure expansion caused by the presence of other flavor compounds in aqueous solution,was conducive to the increase of its binding sites,and the overall binding ability was improved.While limonene,laureene and undecanal were mixed in pairwise,the release promoting effects of SPI aqueous solution on limonene and laureene were all enhanced compared with that of limonene and laureene alone,while the release of undecanal had no significant difference.SPI concentration had no effect on the release of linalol,geraniol and citronellol.With the increase of SPI concentration,the release of limonene,α-pinene and cinnamene was promoted,while the release of the other 9 compounds was weakened.The release effects of pH on the 15 flavor compounds were in two forms.Except limonene,α-pinene and laurene,the release promoting effect of these three compounds was enhanced with the increase of pH,while the release rate of all the other compounds decreased with the increase of pH,that is,the binding force with SPI increased.The degree of SPI denaturation was more complex.With the increase of SPI denaturation,the release rates of linalool,geraniol and citronellol decreased.The release promoting effect of limonene,α-pinene and laureene was weakened.Methylheptenenone and carvone decreased their release promoting ability with the denaturation of 7S,but their release promoting ability increased again with further denaturation.The release rate of other compounds increased,that is,the binding force with SPI decreased.Different stabilizers had different effects on the release of 15 pear flavor compounds in SPI solution.Guar gum affects only a few ester compounds,including heptyl acetate,citronella acetate,linalool acetate and linalool formate.However,xanthan gum was relatively close to CMC and had significant effects on all 15 compounds,significantly reducing the release capacity of each compound,and even reversing the promoting release effect of limonene,α-pinene and laureene.Above results indicate that Flavor compounds of released in SPI system,affected by many factors,affected by the concentration of SPI,SPI structure(or heat denaturation degree),concentration of flavor compounds,flavor compounds pH and itself structure,system of other compounds such as stabilizer and effect of the coexistence of a variety of flavor compounds.Mechanism of action and influence each other more complex.In the future,it should be adjusted according to the interaction factors and influence amplitude of flavor compounds with SPI.