Preparation Of Soy Protein With Better Emulsifying Stability By Enzymatic Modification And Its Application In Ice Cream

According to the requirement of solubility, emulsifying properties and frozen stability ofprotein in ice cream, this paper evaluated the effect of （a） hydrolysis [2.0%～15.0%degree ofhydrolysis （DH）] with Papain,（b） cross-linking with transglutaminase （TGase） afterhydrolysis and （c） before hydrolysis on the emulsifying properties and emulsion stability ofsoy protein isolate （SPI）, and aimed to create a good food ingredient in improving theemulsifying properties in ice cream．With analysis of supernatant protein content, emulsifying activity index and emulsionstability, the effect of three modifications on solubility and emulsifying properties wereinvestigated. The results showed that: SPI hydrolysates, hydrolysates of cross-linked SPI andthe cross-linked products of SPI hydrolysates displayed increases in solubility andemulsifying properties compared to unmodified SPI. The supernatant protein content andemulsifying activity index of SPI hydrolysates increased with the improvement of DH,compared to the decrease of emulsion stability. At2%DH, hydrolysate （DH2） resulted ingreater emulsifying activity index and emulsion stability than that observed in otherhydrolysates. The cross-linked products of SPI hydrolysates displayed increases in solubilityand emulsifying properties as the DH of SPI hydrolysates increased. Hydrolysates ofcross-linked SPI displayed increases in the supernatant protein content and emulsifyingactivity index. Overall, DH6-C displayed a better emulsifying property. The emulsifyingactivity index of DH6-C were greatly improved at pH3～6, and the emulsifying activityindex of DH6-C at pH4.6increased by526.49%compared to SPI. The emulsion stability ofDH6-C were greatly improved at pH4～6, and the emulsion stability of DH6-C at pH4.6increased by79.42%compared to SPI. The emulsifying properties of DH6-C were increasedwithin protein concentration （0.5%～4.5%w/v）. The emulsifying activity index and emulsionstability of0.5%DH6-C respectively increased by103.37%、115.41%compared to0.5%SPI.With analysis of particle size, centrifugal creaming rate, oiling off and the flocculationand coalescence degree of O/W emulsions, the effect of three modifications on SPI emulsionstability after cold （4℃） and frozen （-18℃） storage for7days were investigated. The resultsshowed that: All of these three modifications could improve SPI emulsion stability after coldand frozen storage. Sauter mean diameter (D_3,2) and centrifugal creaming rate of O/Wemulsions prepared with SPI were increased at cold storage, with higher flocculation degree（292.55%）. Compared to SPI O/W emulsion after cold storage, D_3,2, centrifugal creaming rate,oiling off and the flocculation degree of O/W emulsions prepared with three modificationswere lower, almost without coalescence. The O/W emulsions prepared with lower DHhydrolysates （DH2, DH6） displayed greater decrease in D_3,2, centrifugal creaming rate and oiling off than that of higher DH hydrolysates （DH10, DH15）. The D_3,2, centrifugal creamingrate and oiling off of O/W emulsions prepared with cross-linked products before and afterhydrolysis decreased with the increase of DH （0%～6%）. D_3,2and centrifugal creaming rateof O/W emulsions prepared with SPI were increased at frozen storage, with highercoalescence degree （1063.43%）. Compared to SPI O/W emulsion after frozen storage, D_3,2,centrifugal creaming rate, oiling off, the flocculation and coalescence degree of O/Wemulsions prepared with three modifications were lower. The stability of O/W emulsionsprepared with three modifications at frozen storage displayed the same trend as theseemulsions at cold storage. Overall, the O/W emulsions prepared with DH6-C displayed abetter stability at cold and frozen storage. Compared to SPI O/W emulsions at cold storage,D_3,2, centrifugal creaming rate and oiling off of DH6-C O/W emulsions respectivelydecreased by35.41%,32.49%,60%, almost without flocculation and coalescence. Comparedto SPI O/W emulsions at frozen storage, D_3,2, centrifugal creaming rate and oiling off ofDH6-C O/W emulsions respectively decreased by38.27%,55.05%,48.08%, and theflocculation and coalescence degree decreased by36.72%、93.56%.The effect of the partial substitution of skim milk powder with DH6-C on the qualitycharacteristics of ice cream showed that: The addition of DH6-C at10%～30%levelpromoted an improvement in the viscosity, consistency coefficient and the stability of theregular-fat and low-fat ice cream mix. The increase of DH6-C substitution led to higheroverrun, a greater melting resistance and lower hardness value. Compared to regular-fat icecream control, the consistency coefficient, fat destabilization, overrun of DH6-C at10%levelice cream increased by23.46%,23.55%,8.76%, and the hardness value decreased by10.79%.DH6-C ice cream at30%level greater improved the quality of low-fat ice cream. Comparedto low-fat ice cream control, the consistency coefficient, fat destabilization, overrun of DH6-Cat30%level ice cream increased by214.16%,188.94%,11.87%, and the hardness valuedecreased by1.38%.