| Quinoa is the only food in which a single plant can meet the basic nutritional needs of the human body.In 2020,the planting area of quinoa in China is about20,000 hectares,of which Gansu Province has a planting area of about 10,000hectares,and"Longli 1"is the main variety in Gansu.Quinoa is a high quality source of plant protein,with a protein content of 12～23%.In recent years,much attention has been paid to the development and utilization of high quality plant proteins.In order to further develop and utilize quinoa albumin,the main variety"Longli 1"in Gansu Province was used as experimental material and ultrasonic assisted extraction was used in this study.By optimizing the extraction process parameters and the physicochemical properties of albumin（subunit distribution,amino acid composition,endogenous fluorescence,UV spectrum,thermal stability,scanning electron microscope,Fourier transform infrared spectrum（FTIR）,600MHz nuclear magnetic resonance）,functional properties（solubility,oil holding capacity,foaming and foam stability,emulsification and emulsion stability,flexibility）,and in vitro digestion characteristics（hydrolysis degree,the release of free amino acids,antioxidant activity,FTIR and structure under scanning electron microscope）were studied in detail.The purpose of this study is to provide a basis for further processing and utilization of quinoa albumin.The research results are as follows:1.The protein content of quinoa seed of"Longli 1"was 15.78±0.37%.According to Osberne classification,the contents of albumin,globulin,prolamin and glutenin were 34.96%,23.86%,9.22%and 3.49%,respectively.The extraction yield of quinoa albumin can reach 63.25 mg/g under the conditions of ultrasonic power 354W,ratio of material to liquid 1:25.5 g/m L,ultrasonic time 40min and water bath temperature 36.9℃.2.The isoelectric point of seed albumin from"Longli 1"is 3.4,which is composed of multiple subunits,and the relative molecular weights of subunits are37.34,33.94,28.95 and 17.97 KDa,respectively.Albumin contains 17 kinds of amino acids by acid hydrolysis,in which the ratio of essential amino acids to total amino acids is 32.95%.The contents of Glu,Asp and Arg of albumin are relatively high,and cysteine（Cys）is the first limiting amino acid of albumin.At room temperature,the contents ofα-helix,β-folding,random coil andβ-angle of albumin were 30.85%,30.58%,27.38%and 11.19%,respectively.3.The structure of albumin changed obviously after heat treatment at 50～121℃for 30min.Before 80℃,the free thiol and disulfide bond contents of albumin increased with the increase of temperature,while the disulfide bond decreased gradually.The free thiol reached the maximum value of 2.15 nmol/mg at 80℃,while the disulfide bond reached the minimum value of 3.75 nmol/mg at 80℃.The maximum pyrolysis temperature of albumin is 316℃,and the maximum peak value of DTG increases between 100℃and 121℃.After heat treatment at 50～121℃for30min,the endogenous fluorescence intensity（FI）decreased continuously,and the maximum absorption wavelength(λmax)increased.The ultraviolet absorption intensity decreases continuously,and the maximum absorption wavelength(λmax)has a blue shift of 4nm.The content ofα-helix decreased gradually,and the content of random coil increased.The protein structure unfolded and changed to disorder.Scanning electron microscopy（SEM）showed that the albumin was disaggregated and then aggregated again,forming a compact aggregate.The surface pores increased gradually,and the surface morphology changed significantly at 121℃,and the pores reached the maximum.The 600 MHz NMR spectra showed that the normalized relative percentage of albumin in the range of 1.77～2.28 ppm and 2.28～2.79 ppm was the lowest at 121℃,which were 13.66%and 0.02%,respectively,and were 6.80%and6.16%lower than that in the untreated group.In the range of 2.79～3.30 ppm,the normalized relative percentage was the smallest at 70℃,which was 8.95%.In the range of 3.30～3.81 ppm,the maximum normalized relative percentage was 5.70%at70℃.4.When the temperature was 60℃,the solubility,emulsification and emulsion stability of albumin reached the maximum value,which were 94.73%,13.40 m2/g and 70.96%,respectively.At the temperature of 70℃,the oil holding capacity and foaming capacity reached the maximum values,which were 4.55 g/g and 103.17%,respectively,but the foam stability was the minimum,which was 39.85%.After that,with the increase of temperature,its solubility,emulsification and emulsification stability,oil holding ability and foaming ability began to decrease with varying degrees,but the foam stability increased continuously.From 50℃to 121℃,the flexibility increases with the increase of temperature,and reaches the maximum of0.348 at 121℃.5.When the concentration of NaCl was 0.75 mol/L,the solubility and foaming ability of albumin from"Longli 1"seed were 97.73%and 109.83%,respectively.When the concentration of NaCl was 0.50 mol/L,the emulsification and emulsion stability were the best,which were 13.76 m2/g and 66.68%,respectively.The foam stability was the best when the concentration of NaCl was 1.00～1.25 mol/L.6.When albumin was digested in simulated stomach digestion environment for 2h,the degree of hydrolysis（DH）was 18.56%,and the content of free amino acid was0.876 mg/100m L.The particles of protein were significantly smaller,disordered arrangement showed dense structure,and there were many pores.The contents ofβ-angle,β-fold,α-helix and random coil structure were 16.30%,49.48%,18.88%and 15.34%,respectively.After simulated digestion of small intestine for 3.0h,DH was 39.60%,the content of FAA was 4.546 mg/100m L,the particles of protein became flocculent particles,the surface area was further increased,The contents ofβ-angle,β-fold,α-helix and random coil structure were 17.29%,33.11%,34.57%and 15.02%,respectively.After gastrointestinal simulated digestion,the DPPH·,ABTS+·clearance rate,total reducing power,Fe2+chelating rate and Cu2+chelating rate of albumin digested products reached 58.43%,79.67%,0.280,67.99% and 15.74%,respectively. |
