Study On The Enzymatic Modification Of Defatted Egg Yolk Protein

Egg yolk protein was generated as a co-product of egg yolk lecithin exreaction. ThisEYP had poor functionality caused by the organic solvent treatment during extraction.However, the EYP accounts for one-third of the egg yolk dry weight and has characteristics ofbeing absorbed easily and a balanced amino acid ratio, so it’s a kind of protein with largequantity and high quality. This work mainly studied the influence of limited proteasehydrolysis on EYP, determined the changing rule and correlation between its functional andphysicochemical properties, and made an application research on EYP hydrolysates (EYPh).This paper can give the theoretical guidance on the corralation between the structure andfunction of EYP, and provide a new ideas about the comprehensive utilization of EYP.Firstly, the influence of limited hydrolysis on the functional properties of EYP withdifferent enzyme types at different degrees of hydrolysis (DH) was analyzed. The resultsshowed that the trypsase had the most significant influence on the solubility of EYP, it canreach49.21%at DH8%; For foaming capacity (FC) and foam stability (FS), the papainimproved FC and FS of EYP most significantly, the FC was170%and FS was85%at DH5%,being3.09times and2.24times of the original EYP, respectively. For emulsifying acticity(EA), the modification of alcalase and papain were more apparent than others and theyreached to the best condition at DH8%and DH5%, respectively. The alcalase improved themost significantly for its emulsion stability (ES), and reached to the maximum at DH8%.Secondly, the functional and physicochemical properties of papain hydrolysis underdifferent DH were studied, then the correlation between them was analysed. For foamingproperties, the increase proportion of peptide below1000and decrease of surfacehydrophobicity(S0) had disadvantage to FC, and the grand average of hydropathy was animportant factor to improve it; The molecular weight distribution was also a key factor to FSand S0within certain limits had a positive correlation to FS. For emulsion properties, EYPhreached the optimal state at DH4%, the increase of S0had a positive effect on theimprovement of EA; ES reached the optimal state at DH6%, the proportion of1000to5000peptide contribute to the stability of the emulsion. The water-holding capacity of EYPhreached the maximum value2.56g/g at DH2%, the trend was correlated with the molecularweight distribution. The oil-holding capacity of EYPh reached the maximum value4.78g/g atDH6%, negatively correlated with the surface tension.Finally, the papain hydrolysate was divided into two parts including supernatant andprecipitation, carried on the analysis and application research. The results showed that EYPhsupernatant could be use as foaming agent, replaced egg white partly to make angle cake. Itcould be made similar to that made by100%egg white when the substitution rate was lessthan10%. EYPh precipitation containing86.28%of the phosphorus, and it can be used as thesources of phosvitin phosphopeptides (PPPs). Through the dephosphorization, chymotrptichydrolysis and metal affinity adsorption, the pure PPPs could be obtained.