Extraction and Purification of Globulin from Juglans mandshurica Maxim and Characterization of Its Functional Properties
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Abstract:
Globulin is a major protein component of walnuts (Juglans mandshurica Maxim) from the Changbai mountain. The walnut is rich in proteins; therefore, it must be further developed and processed for appropriate utilization of the protein resources. Walnut globulin was extracted by optimized Osborne method, and purified by ion-exchange chromatography. Walnut globulin was subjected to a preliminary structural analysis; subsequently, its functional properties were comprehensively compared (and analyzed) against those of soy protein isolates (SPI), in order to provide a theoretical basis for its application in food processing. The prepared globulin contained 80.71% protein content. Anion-exchange chromatography showed four peaks; the relative molecular weights corresponding to these peaks were concentrated in the ranges 14.3~27.0 kU, 18.0~21.0 kU, 30.0~37.0 kU, and 44.3~59.0 kU, as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The essential amino acid content of the prepared globulin conformed to the Adult Standard Recommendation of the FAO/WTO. The differential scanning calorimetry (DSC) spectrogram of the prepared globulin revealed two endothermic peaks, indicating denaturation temperatures of 98.08°C and 155.33°C, corresponding to enthalpy values of 13.06 J/g and 764.80 J/g, respectively. The Fourier transform-infrared (FT-IR) spectrum revealed that the prepared globulin mainly consisted of alpha helical secondary structures. The functional properties of the prepared globulin, excluding foamability and water absorption (which were significantly lower than those of SPI), were observed to be comparable to those of SPI.
