| CGM (Corn gluten meal) is the main byproduct of corn after starch extraction, and peanut meal is the main byproduct of peanut after oil extraction. Both of them are rich in protein and low in price, however, the former has poor processing performance while the latter is not meeting the need of food processing completely. Research shows that enzymatic hydrolysis can improves the processing performance of protein and get a lot of bioactive peptides with different physiological activities. A lot of researches have been conducted on peptides prepared from corn and peanut separately, while no research has been conducted on the composite peptides hydrolyzed from the mixture of corn protein and peanut protein. In the paper researched the extraction method of proteins from CGM and peanut crude protein, determined the hydrolysis technological process of the protein mixture flour by a fractional hydrolysis with two enzymes; compared the desalination effects of three desalination methods of the protein mixture hydrolysates synthetically;Separated the protein mixture hydrolysates by Chromatography Column, then compared the ACE-inhibitory activity of each compositions; Compared the antioxidant activity of each compositions separated by ultrafiltration membranes; The processing performance of the hydrolysates were also researched. This paper was providing theoretical basis and technological support for the industrial production of biologically active peptides. The main research content and results are following:1 Study on extraction technology of corn proteins and peanut protein and determination of suitable mixing proportion of proteinsExtraction with ethanol and deposition with acid were adopted for the extraction of corn proteins from CGM. The product thus obtained contained protein at 90.20±0.47%, crude fat 1.82±0.11%, moisture 5.92±0.21% and ash 4.64±0.10%. Alkaline extraction and acid deposition assisted by ultrasonic wave and microwave were used for the extraction of peanut protein from peanut crude proteins, the optimum conditions were as follows:72w microwave power, pH 9.73, the ratio of meal to solvent 1:28, extracting time 500 seconds, pH4.5 for acid deposition of protein, extracted for 2 times. The extraction rate of protein reached 88.37±0.27% under such conditions, and the product thus obtained contained protein at 88.95±0.39%, crude fat 1.47±0.11%, moisture 5.86±0.21% and ash 4.75±0.10%.The analysis of amino acid composition of the mixtures of aforementioned corn protein concentrate and peanut protein concentrate at different proportions showed that the mixture of corn protein concentrate and peanut protein concentrate at the proportion of 3/1 had a high percentage of the hydrophobic amino acids, especially with the high content of Val and Phe. Therefore, it is the ideal raw material for the preparation of bioactive peptides.2 Study on multiple step hydrolization of the protein mixturesThe protein mixture flour was hydrolyzed by a fractional hydrolysis with alcalase protease and flavorzyme and the optimum hydrolytic process was determined. Discuss the effect of enzyme hydrolyzing to the amino acid composition of the protein mixture. The results showed that:first, taking degree of hydrolysis as criterion,5% substrate, alcalase concentration 6300U/g,55℃, pH9.5 and the hydrolysis time was 210 min, the hydrolysis rate of 27.63±0.07% was measured after the enzyme was inactivated. Second, taking concentration of free amino N as criterion, continued hydrolyzed the aforesaid composite hydrolysates with flavourzyme and its optimum hydrolytic conditions was that:flavourzyme concentration 900U/g, pH7.0,50℃and the hydrolysis time was 3 hours. The concentration of free amino N in the hydrolysate could reach to 1.25±0.09mg/mL Enzymatic hydrolysis has moderate reaction conditions and the amino acid composition of the product had no evident change compare with raw material protein mixture.3 Study on desalination method for composite peptide from protein mixturesComposite hydrolysates were desalted by MWCO100 dialytic bags,001×7, 201×7 iron exchange resin and D3520 macroporous adsorption resin compared their desalination effects comprehensively. The results showed that:The dialysis was not good at desalting, its desalination ratio and nitrogen recovery ratio were low while the iron exchange resin had high desalination ratio and nitrogen recovery ratio. D3520 macroporous adsorption resin had the best desalination effect, when the velocity of flow was controlled to 10 times column volume/h desalination ratio reached to 88.42±0.91% and nitrogen recovery ratio was 89.06±0.87%. After desalination by D3520 macroporous adsorption resin, the hydrophobic amino acids were enriched and its content increased to 66.0% from 50.8%, the ACE inhibitor activity was improved significantly, with its IC50 decreased to 0.257±0.02 mg·mL from 0.309±0.03mg/mL.4 Study on molecular weight and ACE-inhibitory activity of the hydrolysates from protein mixtureThe molecular weight of the hydrolysates from protein mixtures was measured by gel chromatography, and separated the hydrolysates using Sephadex G-25, then compared the ACE-inhibitory activities of different hydrolysate compositions.The results showed that:the gel chromatography analysis proved that the Mn and Mw of the peptides were 1.12×103 and 2.96×103 respectively, and molecular weight distribution was 2.65. Separated the hydrolysates using Sephadex G-25 and collected four components, the ACE-inhibitory activity of compositionⅢwas the highest.5 Study on antioxidant activities of different compositions from protein mixturesThe hydrolysates were separated by ultrafiltration membranes and two compositions were obtained:compositionⅠ(3-6kD) and compositionⅡ(<3kD). The antioxidant activities of composite hydrolysates, compositionⅠand compositionⅡ were investigated. Measured their OH·,O2-·, DPPH·and ABTS+·radical scavenging activity within a certain concentration range. The results showed that all composite hydrolysate compositions had antioxidant activity and existed dose-effect relationship between antioxidant activity and concentration, however, their antioxidant activity were weaker than Vc. OH·, O2-·, DPPH·radical scavenging activity of compositionⅠwas the strongest, followed by composite hydrolysates, while composition II had the lowest antioxidant activity. However, ABTS+-radical scavenging activity of composite hydrolysates was without a doubt significantly higher than compositionⅠand compositionⅡ.6 Processing performance of composite peptidesDissolvability, viscosity, oil-adsorbing ability, foaming characteristics and foam stability, emulsifying ability and stability of the protein mixture and freeze dried hydrolysates were studied. The results showed that, solubility of the hydrolysates was good and its NSI did not differ significantly at the range of pH2-9 (P>0.05) while the protein mixture had difficult solubility and its NSI influenced by pH greatly, the NSI of protein mixture was low at the range of pH5-7 and rised when deviations from this range. Viscosity of the protein mixture was linked to its solubility, it increased rapidly while concentrations greater than 10%, however, the hydrolysates featured low viscosity even at a high concentration; Oil Absorption Capacity of the hydrolysates was obviously higher than protein mixture, and it as the temperature rises gradually reduced; The hydrolysates had better foaming ability compared to the protein mixture, but both of them had bad foam stability; Emulsifiablity of the protein mixture was good and highly influenced by pH at low temperatures, however, emulsifiablity of the hydrolysates had no significant change and maintain about 40%, both emulsifying stability was negatively affected at high temperatures. In summary, enzymolysis can obviously improve processing performance of the protein mixture, the hydrolysates were more suitable for food processing. |
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