Improvement of egg yolk powder properties through ultrasound coupled sodium sulfite pretreatment assisted enzymatic hydrolysis and underlying mechanism

Egg yolk is an excellent protein source for the production of bioactive peptides. However, the recent method need to remove lipid first which involves wastage and pollution of organic reagents. Therefore, the process of directly using oily yolk powder to prepare egg yolk peptides has attracted much attention. This study developed a one-step process to simultaneously extract oil and hydrolyze proteins based on an ultrasound coupled sodium sulfite pretreatment (UCSSP) assisted enzymatic hydrolysis for egg yolk powder. Results showed that UCSSP increased the oil extraction rate from zero to 75 % with 59.35 g/L of soluble protein and 33.99 g/L of peptide. Further analysis of the underlying mechanism demonstrated that ultrasound pre-treatment could change the secondary structure of EYP while sodium sulfite pre-treatment softened the protein and induced more hydrophobic groups exposed, thus inducing more lipoprotein released for hydrolysis. In addition, the proportion of peptides ranging from 180 Da to 3000 Da in the UCSSP group increased from 31.19 % before to 79.74 %, which was 31.27 % and 6.16 % higher than that of UP and SP. Furthermore, the obtained peptides showed obvious activities in uric acid-lowering, anti-obesity and antioxidant with 56.24 % inhibition in XOD activity and close antioxidant activity to vitamin C, implying it a potential health product. •Ultrasound coupling sodium sulfite pretreatment was developed for egg yolk power hydrolysis.•Ultrasound altered protein structure, while sodium sulfite enhanced lipoprotein release.•UCSSP increased surface hydrophobicity and decreased the content of disulfide bonds for EYP.•UCSSP increased the protion of peptides between 180 Da and 2000 Da.•UCSSP enhanced the uric acid-lowering and antioxidant activities of peptide segments.