Study Of Preparation And Emulsiyfing Properties Of Buckwheat Protein Isolate-dextran Conjugates

Buckwheat protein has high nutritional value with balanced amino acids compositionand multiple physiological functions like lowering cholesterol, antioxidation, lowering bloodpressure, antitumor and so on. Currently, the research does not go far enough on thefunctional properties of buckwheat protein as a food ingredient. This paper studied thefunctional properties and structure of buckwheat protein isolate-dextran conjugates preparedby wet-heated Maillard reaction, which aimed at providing scientific theory basis for thecomprehensive development and utilization of buckwheat protein.Buckwheat protein isolate-dextran conjugates were prepared at60℃and70℃. It wasstudied about the effects of different reaction time on solubility, emulsification and browningdegree. The results showed that the emulsifying activity and emulsion stability of theconjugates were both enhanced significantly, compared with the native protein and heatedprotein. The conjugates prepared at70℃for6h or60℃for24h showed good emulsifyingproperties with little browning.The effects of glycosylation on physicochemical properties and structure of buckwheatprotein were analyzed by measuring the physicochemical properties and structure ofconjugates prepared at70℃for6h, which was in order to explore the internal mechanism ofimprovement of functional properties. Compared with the native buckwheat protein isolate,the solubility of the conjugates was higher at pH4-4.5. DSC analysis indicated that thedenaturation temperature of the conjugates was increased to105.45℃with improved thermalstability, while that of native protein is only101.34℃. The measurement results of rotationalrheometer showed that the conjugates had higher viscosity and lower mobility while theconjugates were shear-thinning pseudoplastic fluids just the same as native protein. Thesoybean oil-water interfacial tension absorbed by the conjugates was less than that absorbedby native protein. The fluorescence spectra showed the conjugates had lower polarity andenhanced hydrophobicity. The formation of conjugates was verified by SDS-PAGE (bothprotein and carbohydrate staining). The results of far-UV circular dichroism showed thatbuckwheat protein isolate-dextran conjugates had less α-helix and more random coil in thecomposition of secondary structure.The emulsion stabilized by buckwheat protein isolate-dextran conjugates was preparedby high pressure homogenization and research was carried out about the effects of pH, ionicstrength on the emulsion stability by droplet size analysis and ζ-potential measurement withthe emulsion stabilized by the native buckwheat protein as control group. The results showedthat the droplet size of emulsion stabilized by the conjugates was smaller at the same pH,especially at the isoelectric point and the magnitude of changes of its droplet size was smallwith increasing ionic strength, which indicated the emulsion had good stability and wasprobably because the glycosylation increased the steric stabilization at emulsion dropletinterfaces and delayed or hindered aggregation between droplets. The ζ-potentialmeasurement results showed that the isoelectric point of the conjugates absorbed at emulsion droplet interfaces had slightly acid shift, but the emulsion had smaller absolute value of ζ-potential. Besides, ζ-potential changed more slightly with increasing NaCl concentration. Themorphology of the emulsions observed by Confocal Laser Scanning Microscope also showedthat the emulsion prepared by conjugates had smaller droplet size with better dispersion.Experiments also found that emulsion stability prepared by the conjugates and native proteinhad been improved with varying degrees after heated at95℃for15min.