Enzymatic Hydrolysis Of Soybean Protein By Mould Proteases Under Acidic Condition And Its Hydrolysates Characteristics

Soy proteins are very important protein source for human being and livestock. Enzymatichydrolysis of soy protein can enhance its functional properties and nutritional values, itshydrolysates are primarily used as functional food ingredients, flavour and nutritiousenhancers, protein substitute, and clinical products. The main problem associated withproteolytic hydrolysis of soy protein is production of bitter taste. Therefore, exploring newproteolytic enzymes or multiple enzymatic hydrolysis such as combination of exo-peptidaseand endo-peptidase could be used to reduce bitterness while increasing degree of hydrolysis.In this thesis, we investigated the differences in protease activity and proteolysis between A.elegans and R. oligosporus extracellular under acidic conditions (pH3.0-6.0). Then combinedAlcalase, commercial common alkaline protease, with those two mould proteases respectivelyto hydrolyze soy proteins, and compared their hydrolysis catalytic properties. Moreover, themolecular weight distribution, nutritional value and antioxidant activities of the crudepeptides powder, which obtained from combination of Alcalase and R. oligosporus proteasestreatment, had been determined. Main conclusions are as follows:(1) The activity of the R. oligosporus protease was higher than that of A. elegans whenpH<6.0, but both proteases exhibit considerable degradation of soybean protein at pH5.5and6.0respectively. The degree of hydrolysis (DH) was about40%and water-soluble protein(WSP) content was about50%. The bitterness values were below1.0, and hydrophobic aminoacids accounted for60%of total free amino acid content. But the SDS-PAGE reveals thatthese proteases had different cutting sites on peptide polymers.(2) In the double enzymatic hydrolysis, the WSP, DH and amino nitrogen content of thehydrolysates were greatly increased. There had no significant difference between A. elegansand R. oligosporus proteases when at the same condition of the enzyme and substrateconcentration ratio. But for the same kinds of protease, the results were10-20%higher atcondition of600u/g than that of300u/g. Double enzymatic hydrolysates of soy proteinfrom Alcalase and R. oligosporus proteases treatment had a WSP content of80%, DH of50-60%, and amino nitrogen of0.58-0.7%. The hydrolysates had no bitter taste, and thecolor and flavor were both good. (3) The crude peptides powder, produced by double enzymatic hydrolysates of soy proteinfrom Alcalase and R. oligosporus proteases, had good performance and stability in solubilitywithin pH range of3.0-8.0, which maintained the NSI over80%. The total essential aminoacid (EAA) was close to SPI, but the EAA was closer to ideal amino acids pattern recommendby the FAO/WHO than that of SPI, except the valine. The GPC profiles showed the molecularweight distribution of the peptides powder was at range of1300-7000Da,70%of the peptideshad molecular weight of less than7000Da, and50%were less than2700Da. Moreover, thepeptides powder performed strong capacity of anti-oxidation at concentration of2%, whichthe inhibition rate of DPPH free radicals was about88%, reducing power was almost triple ofSPI, and chelating rate of Fe2+could reach to80-90%.