| As an important new resource food,Haematococcus pluvialis is not only a "concentrated product" of natural astaxanthin,but also a potential protein resource.Algal protein has various biological activities such as anti-oxidation,blood pressure lowering,anti-tumor,anti-thrombosis and immune regulation,and it will have broad development prospects in the fields of food,health products,medicine and dyes.It is estimated that in 2030,the size of the global plant protein market will soar from US$4.6 billion to US$85 billion.Algae,due to its advantages of strong controllability,high unit land production,low carbon and even negative carbon production,may surpass soybeans and become The largest source of alternative protein.At present,the cultivation scale of Haematococcus pluvialis in my country is continuously expanding,and the production of by-products of Haematococcus pluvialis after extracting astaxanthin has increased,resulting in a large loss of protein resources.In order to improve the added value and comprehensive utilization of Haematococcus pluvialis,this paper used alkaline extraction and acid precipitation to extract Haematococcus pluvialis protein,and systematically studied the structure and functional characteristics of Haematococcus pluvialis,the main research results are as follows :(1)To study the effect of repeated freeze-thaw method,grinding method and high-speed homogenization method on the protein extraction rate of Haematococcus pluvialis.The research results show that the high-speed homogenization method has the best extraction effect,the extraction rate is high and the time is the shortest,and the extraction rate can reach about 70% after the wall is broken in 30 minutes;the grinding method is followed by the extraction rate of 60% after 90 minutes of grinding.The extraction effect by the melting method is the worst,and the extraction rate is only about 30% in 36 h.(2)Explore the influence of the four factors of extraction solution pH,material-liquid ratio,extraction time and extraction temperature on alkaline extraction of Haematococcus pluvialis protein.The best extraction conditions were obtained through single factor test and response surface optimization test: pH 12,material-to-liquid ratio 1:44,extraction time 150 min,extraction temperature 56?.Under these conditions,the protein extraction rate reached 82.19%.(3)The isoelectric point of Haematococcus pluvialis residue protein is 4.2.Isoelectric point precipitation method and two-step ammonium sulfate precipitation method are used to precipitate protein,and the protein precipitation rates are 98.88% and 87.63% respectively,so the isoelectric point precipitation method is used to precipitate protein.(4)To characterize the structure of algal protein in the residues of Haematococcus pluvialis,systematically study the properties of the subunit composition,secondary structure and microstructure of algal protein.There are 17 kinds of amino acids in Haematococcus pluvialis measured by amino acid analyzer.The amino acid composition is reasonable,which is close to the FAO/WHO model,and is expected to develop into a new protein resource.There are three main subunit bands of Haematococcus pluvialis protein,and their molecular weights are distributed near 14.4 KDa,18.4 KDa,and 38 KDa.Using Fourier infrared spectroscopy(FTIR)analysis and analysis,it is concluded that the secondary structure of Haematococcus pluvialis protein is mainly ?-turn structure,accounting for about 40%,followed by disordered structure,accounting for about 26%.The content of ?-helix is the lowest,accounting for about 14%.It can be observed by scanning electron microscopy that the Haematococcus pluvialis protein is mainly rod-shaped and large-scale,relatively complete,without small fragments,smooth edges,rough surface,there are many tiny holes,more holes mean that protein to water,the oil has better adsorption capacity.The denaturation temperature of Haematococcus pluvialis protein is 30?.Excessive temperature will cause protein denaturation,which will affect the functional characteristics.Therefore,Haematococcus pluvialis protein should be stored in a low temperature environment.The stability of algal protein gradually decreased with the extension of light time.The effect of light on protein stability was not obvious within 3 days.After 3 days,light decreased the content of algal protein rapidly,and the stability became significantly worse.(5)Study the functional properties of the water absorption,oil absorption,solubility,emulsification and foaming properties of algal protein in the residues of Haematococcus pluvialis.The oil absorption of algal protein is 2.49 g/g,and the water absorption reaches the lowest value at pH 4,which is 2.21 g/g,and the water absorption away from the isoelectric point is enhanced.The influence of pH on the solubility of algal protein is consistent with water absorption,with the lowest solubility near the isoelectric point;the NaCl concentration is in the range of 0.1-1.0 mol/L,and the solubility of Haematococcus pluvialis protein increases with the ion concentration While increasing,when the NaCl concentration is greater than 1.0 mol/L,the solubility decreases,indicating that the appropriate addition of neutral salts is beneficial to enhance the solubility of the protein.The emulsification of Haematococcus pluvialis protein decreases first and then increases with the increase of pH.When pH 4 is near the isoelectric point,the emulsification is the worst and the emulsification stability is the highest;when the NaCl concentration is 0.8 mol/L,Haematococcus pluvialis protein has the best emulsification and emulsion stability.The latherability and foam stability of Haematococcus pluvialis protein decreased in the range of pH 2-4,and continued to rise after pH was greater than 4,and the latherability was the worst when pH 4 was near the isoelectric point;at 0-1 mol/L Within the range of NaCl concentration,the foaming and foam stability of Haematococcus protein continuously increased,and reached the highest value when the NaCl concentration was 1 mol/L,and then slowly decreased.It is worth mentioning that the emulsification stability and foam stability of Haematococcus pluvialis protein are extremely strong,and the highest can reach more than 90%. |
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