Study On Physicochemical,Functional And Antioxidant Properties Of Mung Bean Protein And Its Hydrolysate

Mung bean protein（MBP） contains essential amino acids,which could meet the needs of human body for amino acids.MBP is deemed to be a vital source of dietary protein and has many physiological activities and functional properties.Therefore,MBP was used as raw material to study the extraction and optimization of MBP.The effects of different p H values and enzymatic hydrolysis of different proteases on the functional properties of MBP were studied in depth.Alcalase hydrolysates（MPH）with strong antioxidant activity and protamex hydrolysates（MBH）with strong functional properties were treated with different ultrasonic powers to enhance their antioxidant and functional properties respectively.The results of the experiment are as follows.（1）With mung bean as raw material,alkaline-extraction method was used to obtain mung bean was made by proteins.The effect of mung bean flour and distilled water mass ratio,extraction temperature,extraction time and p H value on the mung bean protein extraction rate were studied by single factor experiment.Optimization of protein extraction from mung bean was made by using response surface methodology.The results showed that the optimum extraction conditions for mung bean protein were the ratio between mung bean flour and distilled water mass 1:15,extraction temperature40℃,extraction time 20 min and p H value 9.0.Under these conditions,the maximal extraction rate of mung bean protein was 88.80%.（2）MBP contained six bands of 64,62,48,32,25 and 23 kDa,among which the64,48 and 32 kDa bands consisted of glycoproteins.MBP in an alkaline environment had higher solubility and free sulfhydryl contents,smaller particle sizes,and lower surface hydrophobicity.Rheological analysis showed that MBP at p H 3.0,5.0,7.0 and9.0 exhibited shear-thinning pseudoplastic fluids.A higher shear stress was needed to initiate flow at p H 5.0 than at p H 3.0,7.0 or 9.0.MBP（130 mg/m L）formed self-supporting gels at p H 7.0 and 9.0.MBP had good foaming capacity（125.00%）,emulsion activity index（117.05 m²/g）and emulsion stability index（20.86 min）in alkaline environment.These results provide fundamental information about MBP for use in neutral and alkaline environments as a functional food ingredient.（3）Enzymolysis with the five proteases decreased average particle size,α-helix,β-sheet of hydrolysates.Alcalase hydrolysate had the lowest molecular weight（<10 kDa） and zeta potential（-33.73 mV）.Protamex and papain hydrolysates had higher foaming capacities,emulsification activity indexes and emulsion stability indexes（235.00%,123.07 m²/g,132.54 min;200.10%,105.39 m2/g,190.67 min）than MBP（135.03%,20.03 m²/g,30.88 min）.Alcalase hydrolysate demonstrated the lowest IC₅₀（mg/m L）in ABTS（0.12）,hydroxyl（2.98）,Fe²⁺chelating（0.22）.These results provide support for application of MBPEHs as foaming agent,emulsifier and antioxidant in food industry.（4）Alcalase-hydrolysed MBP hydrolysate（MPH） contained four bands of 25.6,12.8,10.6 and 4.9 kDa,in which 4.9 kDa was the most abundant.Ultrasonic treatment increased the contents of aromatic and hydrophobic amino acids in MPH.Ultrasonic treatment decreased the content ofα-helix of MPH and increasedβ-sheet andβ-turn compared to MPH.MPH-546W（ultrasonic treatment 546 W,20 min）had the lowest average particle size（290.13 nm）,zeta potential（-36.37 m V）and surface hydrophobicity（367.95 A.U.）.Antioxidant activities of ultrasonicated-MPH increased with the ultrasonic power,achieving the lowest IC₅₀（mg/m L）of 0.1087（ABTS）,1.796（hydroxyl）,1.003（superoxide anion）and 0.185(Fe²⁺chelating ability)in 546 W power.These results indicated ultrasonic treatment would be a promising method to improve the antioxidant properties of MPH,which would broaden the application scope of MPH as bioactive components in the food industry.（5）Protamex-hydrolysed MBP hydrolysate（MBH） contained five bands of 25.8kDa 12.1 kDa 5.6 kDa 4.8 kDa and 3.9 kDa.Ultrasonic treatment increased the contents of essential amino acid in MBH.Ultrasonic treatment decreased the content ofα-helix and random structure of MPH and increasedβ-turn compared to MPH.Ultrasonic treatment（112 W-330 W）increased the zeta potential and fluorescence intensity（intrinsic and surface hydrophobicity）of MBH.MBH-330W（ultrasonic treatment 330W,20 min）had good foaming and emulsification properties.These results showed that ultrasonic treatment could improve the functional properties of MBH.