Modification Of Alcohol Leached Soy Protein Concentrate Under Controlled Heating Conditions

Alcohol leached soy protein concentrate (ALSPC) has lower NSI (5-12%) and poor functionality due to denaturation of protein by alcohol. Thus modification of ALSPC through heating treatment was studied systematically to extend its application.Commercially available ALSPC was used as raw material. Modified soy protein concentrates (MSPC) were prepared by controlled the condition of heating modification. The effects of different heating conditions on solubility, emulsifying property and gelation property were investigated. Subsequently the functionality and protein structure of MSPC were further studied to clarify the mechanism for heating modification of ALSPC, and also to supply some theoretical basis for modification and application of ALSPC.First the effects of heating modification under controlled techniques including heating temperature, protein concentration and the amount of NaOH on the functionality of MSPC were studied. The results showed that the solubility of ALSPC was obviously improved by heating modification (NSI approximate 60%) through 110°C to 150°C, the emulsifying strength was increased from 18g to 110g after treatment, and the gelation strength was apparently improved from 37g to 400g.We found the best technology was that the temperature was 140°C,the protein concentration was 8% and the alkali addition was 0.5% through orthogonal experiment,the gelation was 400.068 under this technology which is close to that of commercial functional soy protein concentrate (FSPC).This indicated that heating modification had the highest impact on the gelation of ALSPC.Subsequently the effects of heating modification on the gelation and protein structure of MSPC were further investigated. The strength and storage module G'of MSPC gel increased with the increase of heating temperature, and the space between storage module G'and loss module G''also increased.The microstructure of soy protein gels obtained by SEM has witnessed the results from large deformation textural and rheological determination.The results from size exclusion chromatography showed that the contents of soluble aggregates in MSPC also increased with the increase of heating temperature. The results from electrophoresis reflected the variation of soy protein structures during heating.Heating modification didn't cause large changes on the subunits of soy protein.But the aggregates linked by the disulfide bonds occurred with the heating modification,especially the temperature above 130°C.These aggregated seems to be related with the gelation property of MSPC.The surface hydrophobicity of MSPC increased compared with the controlled ALSPC. The determination of free SH content and total SH content showed that new disulfide bonds occurred by the linkage of free SH, which is also contributed to the gelation property.Finally the application of ALSPC and MSPC on sausage was studied. The results showed that the sausage with MSPC content of 7% obviously improved its textural, sensory and water-holding property and reduced the losing of braise and cook.