| Peanut is an important source of oilseeds protein. Peanut protein has poorer functionalproperties compared with other plant proteins, therefore has limited industrial applications.Glycation is known to be a green method for the protein modification and could greatlyimprove the functional properties of food proteins. In this study, it was found that solubility,emulsifying properties and physiochemical properties of peanut protein films has beensignificantly improved by glycation, as well as the physiochemical properties and structuralproperties of films were significantly affected by the degree of glycation, flavor encapsulationand controlled release were also accomplished in glycated peanut protein films. Thesefindings have provided fundamental theoretical basis for value-added development of peanutprotein and its application in active package. The specific findings were listed below:1. Peanut protein isolate (PPI) was able to conjugate with dextran (Dex) or gum arabic(GA) through glycation under dry-heated treatment, and PPI was more inclined to glycatewith GA than Dex. Conarachin II in PPI could more easily participate in the glycationreaction. After7days glycation, α-helix in PPI-Dex and PPI-GA conjugates decreased to57.4%and53.2%, the conjugates were also possessed of more flexible protein sencondarystructure, lower surface hydrophobicity and less compact tertiary structure than native PPI.Moreover, the solubility of PPI-Dex conjugates was greatly improved for pH3-9, while thatof PPI-GA conjugates was improved at pH>7and the isoelectric point was not obvious. Theemulsifying ability index of PPI-Dex and PPI-GA conjugates increased to207.0and242.9m2/g, respectively. Compared with films prepared from PPI-polysaccharides mixtures, filmsprepared from the conjugates had darker color, lower moisture content (MC) and total watersolubility (TSM), better elongation and decreased water vapor permeability (WVP).Compared with films prepared from PPI-Dex conjugates, films prepared from PPI-GAconjugates had increased ΔE value and poorer elongation, however, PPI-GA glycated filmshad decreased TSM and WVP as well as increased tensile strength (TS).2. Compared with classical heating, ultrasonic treatment was able to accelerate theglycation within shorter time, and structure feature analyses suggested that glycated PPIobtained by ultrasonic treatment had less α-helix and more β-structures, higher surfacehydrophobicity and less compact tertiary structure. These structural modifications may be thereason of improved solubility, emulsifying ability and stability of the ultrasound treatedconjugates compared with classical heating treated conjugates. However, films prepared fromultrasound treated conjugates had darker color, higher MC and TSM, poorer mechanicalproperties and higher WVP than those prepared from classical heating treated conjugates. PPIwas more inclined to glycate with Dex than GA under both classical heating and ultrasonictreatment. Films prepared from PPI-Dex conjugates was more plastic, while those preparedform PPI-GA conjugates had better TS and lower WVP. Among all three glycation methods,emulsifying ability of conjugates prepared from classical heating and ultrasonic treatmentwere poorer than that prepared from dry-heated treatment, and the overall performance offilms prepared from dry-heated conjugates were better than films prepared from the other two methods, with films prepared from PPI-GA dry-heated conjugates the best.3. Conarachin II in PPI first participate in the glycation reaction, as the glycationcontinued to6days, acid arachin also participate in the reaction process. As the dry-heatingtime increased, the degree of graft of PPI-GA conjugates increased gradually, and PPI-GAconjugates gradually had more flexible secondary structure, less compact tertiary structure, aswell as three-dimensional network less resistant to flow. After3days glycation, PPI-GA filmshad increased ΔE value, MC and TSM decreased to9.43%and48.81%, respectively, WVPvalue decreased to71.2×10-11g m-1s-1Pa-1, TS increased to1.76Mpa, while elongationremarkably decreased to37.4%. As the glycation continued, the color of films become darker,the tensile strength decreased, and the WVP, elongation, MC and TSM increased gradually,the films become more plastic. Moreover, the degree of crosslinking between PPI and GA infilms also increased as the glycation continued, the strength of water/conjugates andglycerol/conjugates chains interactions in the films gradually become more present, andthermal stability of films were gradually enhanced. Structural analysis indicated that PPI-GAfilms had more amorphous structures, as well as more stable film structure network as thedry-heating continued. Hydrophobic interactions and hydrogen bonds still existed in the filmnetwork prepared from PPI and PPI-GA mixtures, after glycation, disulfide bonds played apredominant role in the film network.4. The retention of nonpolar flavor compounds was better than that of polar flavorcompounds in PPI-GA films. The retention of1-decanol significantly increased, and the initialrelease rate and first-order kinetic constant during the storage both significantly decreasedafter glycation. As the glycation continued, the retention of1-decanol gradually increased,while the initial release rate and first-order kinetic constant during the storage also graduallyincreased. After3days glycation, the TS increased to1.47Mpa, elongation decreased to38.9%, WVP value decreased to83.6×10-11g m-1s-1Pa-1, and contact angle values increased to94o. However, TS gradually decreased, elongation and WVP gradually increased, and thestructure of films become more uniform as the glycation continued. Pearson correlation testshowed that the retention of1-decanol was correlated with the emulsifying ability of PPI-GAconjugates, as well as the elongation of films, while the release rate of1-decanol duringstorage was correlated with TS, WVP values and contact angle values of PPI-GA films. |
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