Preparation And Properties Of Cottonseed Protein And Functional Peptides

Cottonseed protein is a kind of high quality protein resource,which could make up the deficiency of protein resource in China.Enzymatic hydrolysis could significantly improve the functional properties of cottonseed protein and the cottonseed peptides obtained from hydrolysis also exhibit multiples of biological activities.The paper aimed to improve the utilization of cottonseed protein and prepare functional cottonseed protein and peptides.In this study,the byproduct of dephenol cottonseed-cottonseed meal was used as the raw material.The optimal extraction and purification conditions of cottonseed protein were analysed,and the high purity of cottonseed protein(93.10%)was obtained;the purified cottonseed protein was hydrolyzed to optimize the process of obtaining the cottonseed polypeptide,and the functional properties of cottonseed peptides under different hydrolysis degree were studied;cottonseed polypeptide ferrous chelate was obtained by hydrolysis of cottonseed polypeptide with ferrous ions chelated under optimized process conditions.The main points and contents are summarized as follows:(1)The optimized process of enzymatic and ultrasonic assisted extraction of alkali extraction and acid precipitation of cottonseed protein was: pH 11.0,temperature 45 ?,ultrasonic power 190 W,extraction time 120 min.The extraction rate reached 74.16% under these conditions.Compared with the traditional alkali extraction and acid precipitation,the extraction rate of ultrasonic-assisted method increased by 23.85%.(2)Glucoamylase was used for the hydrolysis of cottonseed crude protein to improve the purity of protein.The optimal process conditions were established as follow: pH 4.5,temperature 60?,hydrolysis time 120 min,the amount of enzyme 0.4%,and liquid to ratio of solid 9:1.The purity of the protein was 90.51% under these optimal conditions.The content of purified cottonseed protein can be further improved after two times purification,thereby the purity reached 93.10%.Relative molecular weight(MW)distribution of protein subunit in purified cottonseed protein was analyzed by SDS-PAGE method.The results showed that the major relative MW of cottonseed protein were 55.9 kDa and 51.3 kDa.(3)The cottonseed protein was hydrolyzed by double enzyme method(Alkaline Protease and Flavourzyme)to prepare the cottonseed peptide.The hydrolysis conditions were optimized with the degree of hydrolysis as the response index.The optimal hydrolyzation parameters to prepare cottonseed peptide were: pH 10.0,temperature 60?,enzyme concentration 6420 u/g.Under these conditions,the optimal degree of hydrolysis degree was 29.27%.The amino acid content of cottonseed peptide was higher,and the flavor protease was added to remove the bitter taste of small molecular peptides,which made the cottonseed peptide with special flavor.The functional properties of cottonseed peptide were studied under different hydrolysis degree.The results showed that: with the increase of the degree of hydrolysis,solubility,moisture absorption,oil absorption,emulsification,emulsion stability and foaming ability of cottonseed peptides were improved,but the foam stability was weaken.The solubility was the minimum when pH was 4.0;moisture absorption continued to increase as the extention of strorage periods;oil absorption showed a downward trend with the increase of temperature;emulsification and emulsion stability reached the minimum when pH was 5.0;The foaming ability and foam stability showed the opposite trend with the increase of hydrolysis.(4)The functional cottonseed peptides with antioxidant properties were obtained by using ferrous chloride using chelation method.Results showed that the optimization of the chelating process was p H 7.0,solution concentration 3%,peptide iron mass ratio 3:1.The chelating rate was 60.02% under these conditions.The UV absorption spectra showed that the absorption peak of the peptide iron chelate was changed compared with the non chelating cotton seed peptide;The infrared scanning spectroscopy results showed that the absorption peaks of both before and after the chelate were shifted,which indicated that the chelating reaction occurred during the process.The antioxidant activities of peptide iron chelate was evaluated by DPPH free radical inhibition test,·OH radical scavenging test and total antioxidant capacity.The results showed that the peptide iron chelate exhibited antioxidant effect.