Controled Hydrolysis Of Salted Egg White Protein And The Application Of Its Hydrolysates

Salted egg is one of the most traditional and popular egg products in C hina, with annual production of 2 million tons. Salted egg yolk has been widely used in food production, as an ingredient in moon cake, rice pudding and some bakery products. However, the salted egg white, as by-product of salted egg yolk processing, is unexploited due to its high salt content(8~10%). Most of the salted egg white is discarded as waste, causing the waste of protein resources and environmental pollution. In this study, two novel and feasible methods were developed to utilize salted egg white, by taking full advantage of its chemical and functional characteristics. The research results were as follows.Lysozyme could be extracted from salted egg white, because it would not denature and precipitate in high tempreture while in acidic condition, but protein would. After single factor experiments, the optimal technological conditions of lysozyme extraction were as follows: the dilution ratio was 1:6, p H was 3.0, heating tempreture was 75 ℃, and heating time was 10 min. Under these optimal technological conditions, the enzymatic activity recovery of lysozyme extracting solution was 67.03% and the protein recovery of precipitation was 85.11%.Salted egg white hydrolysates and egg yolk oil could be produced from salted egg white by enzymatic hydrolysis. After single factor experiments, the optimal technological conditions of enzymatic hydrolysis of salted egg white protein(protease: the acid protease; the amount of protease: 0.2%; p H: 3.0; hydrolysis time: 48h; hydrolysis tempreture: 55 ℃) were determined. Under these optimal technological conditions, the protein recovery(PR) and degree of hydrolysis(DH) of salted egg white hydrolysate were 81.09% and 44.02%, respectively. The peptide molecular weight of the salted egg white protein hydrolyzate was mainly smaller than 3000 Da(85.01%), the essential amino acid content was 39.53%, the content of amino acid contributed to antioxidant activity was 63.37%, the ORAC value of salted egg white protein hydrolyzate was 1000.46 mmol TE/g, and the IC50 value of DPPH radical scavenging activity was 7.10 mg/m L.Moreover, under the optimal technological conditions, 2.51 g egg yolk oil could be produced from every 100 g salted egg white, consisting of 37.09% protein and 36.83% lipid. The egg yolk oil could be developed as a kind of healthy and nutritive lipid, with essential amino acid content of 40.22% and unsaturated fatty acid content of 65.74%.On the other hand, the protein hydrolysate of salted duck egg white with degree of hydrolysis of 3%(PHSDEW-DH3%) could be used as food additive for the quality improvement of shrimp. PHSDEW-DH3% could reduce the thawing loss of frozen shrimp by 17.10%, reduce the cooking loss by 12.99%, and increase the cooking yield by 5.63%. Cooked shrimp treated by PHSDEW-DH3% maintained attractive color, with higher hardness and chewiness. SDS-PAGE assay proved that protein bands corresponding to myosin heavy chain and actin disappeared for shrimp treated by PHSDEW-DH 3%, while they were observed in samples treated by mixed phosphates. The results of thermal transitions suggested that PHSDEW-DH 3% improved the thermal stability of shrimp muscle protein.