Effects of Enzymatic Hydrolysis with Cell Wall Proteinase(CEP) on Structural and Functional Properties of Casein

The structural characteristics of casein hydrolyzed by cell wall proteinase(CEP) from Lactobacillus acidophilus were analyzed by granularity and Fourier transform infrared spectroscopy(FTIR). The effects of different degree of hydrolysis(DH 2.4%, 4.5%, 7.1% and8.3%) on functional properties of casein were determined by emulsibility, emulsion stability, solubility, antioxidant activity and ACE inhibitory activity. The results of FT-IR spectra indicated remarkable changes in the chemical compositions and macromolecular conformation of casein after hydrolysis. The secondary structure of casein was changed with the enzymatic treatment. The nanoparticle size analysis showed that the casein particles decreased during the initial hydrolysis time(DH4.5%), but increased for further hydrolysis, which resulted in the highest emulsion stability under DH 4.5%. The emulsibility and solubility of casein first increased and reached the highest when DH was 7.1%, and then decreased with the further hydrolysis. In addition, the casein hydrolysates had certain ACE inhibitory activity and antioxidant properties, and the DPPH removal capacity within a certain range increased as DH and concentration increased. The highest DPPH removal capacity was 35.00%with DH 8.3% and hydrolysates concentration of 5 mg/mL. Therefore, the enzymatic hydrolysis with CEP can effectively improve the structural and functional properties of casein. This research will provide useful theoretical basis for the production of ACE inhibitory peptides derived from casein.