| Macadamia nut is rich in nutritional value and with excellent health benefits,considered as one of the sources of high-quality edible oils and proteins.This work took macadamia defatted meal as the raw material,extracted protein fractions and isolate then investigate the physicochemical,structural and functional properties systematically.The research content mainly includes using Osborne extraction method to obtain albumin,globulin and glutelin,comparing physicochemical and nutritional properties with protein isolate;Further investigate the functional properties of macadamia protein fractions and isolate at different pH values;Comparative analysis the structural characteristics of macadamia protein fractions and isolate as well as changes in secondary and tertiary structures at different pH values.The results showed that:(1)Using Osborne extraction method to obtained three protein fractions and via alkali extraction and acid precipitation method to obtained protein isolate.The purity of albumin,globulin,glutelin and protein isolate was 84.59%,92.33%,81.53% and84.32%,with the yield was 2.39%,11.62%,4.45%,and 12.97%,respectively.The zeta potential result showed that the potential of macadamia proteins ranged from-30 m V to 25 mV at pH 3.0-7.0,and the isoelectric point of the four proteins ranged from 4.49 to 5.61.The amino acid composition showed that the essential amino acid content of macadamia nut protein meets the recommended adult standards of FAO/WHO/UNO with rich in lysine,valine and isoleucine,macadamia proteins can be added as nutritional supplement to foods.It is suggested that the Osborne method can effectively fractionate macadamia nut protein,and the extracted four kinds of macadamia nut are nutritious and have potential for application in the food industry.(2)To investigate the functional properties of macadamia protein fractions and isolate at different pH values.The pH-solubility curve of macadamia proteins was showed a U-shaped.Among them,albumin showed the best solubility at all pH values.The solubility of albumin,globulin as well as protein isolate were reached75% under neutral condition.Similarly,the water-soluble albumin and the salt-soluble globulin also exhibited better foaming and emulsifying properties,and the alkali-soluble glutelin and protein isolate by alkali extraction and acid precipitation are poor in emulsify ability but showed better oil holding capacity.It is suggested that there are significant differences in the functional properties of albumin,globulin,glutelin,and protein isolate,which may be related to differences in molecular composition and conformation due to the extraction environment.(3)To explore the differences in molecular composition and microscopic morphology of macadamia nut proteins,and then study the changes in secondary and tertiary structures at different pH values.The microstructures of albumin and globulin were mainly rod-shaped and globular,while glutelin and protein isolate exhibited disordered structures such as irregular flakes.The SDS-PAGE pattern showed that the glutelin and protein isolate contained more macromolecular subunits,and the albumin was mainly consisted of small molecular weight subunit,meanwhile the globulin contained a relatively high content of intermolecular disulfide bonds.In addition to the main secondary structure of albumin is ?-helix,the main secondary structure of the other three macadamia proteins is ?-sheet.The secondary structure of macadamia proteins under acidic conditions has a higher degree of change than the alkaline environment.Intrinsic fluorescence scanning showed that the macadamia proteins were highly denatured in the acidic environment,and globulin had a higher degree of folding conformation than the other three proteins.It is indicated that different solvent extraction caused structural denaturation of the macadamia protein in different degrees,resulting in difference of its functional properties. |
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