Limited hydrolysis of β-casein by cell wall proteinase and its effect on hydrolysates's conformational and structural properties

Optimisation of enzymatic hydrolysis of beta-casein with cell envelope proteinase (CEP) from Lactobacillus acidophilus JQ-1 to produce the angiotensin-I-converting enzyme (ACE) inhibitory peptides using response surface methodology (RSM). Under optimal conditions (enzyme-to-substrate ([E]/[S]) ratio (w/w) of 0.132 and pH of 8.00 at 38.8 degrees C), the ACE inhibitory activity of hydrolysates was 72.06% and the total peptides was 11.75 mg mL(-1). Scanning electron microscopy (SEM) micrographs indicated that the tightness of the beta-casein surface structure was gradually weakened and small holes appeared after enzymatic treatment, while Fourier transform infrared spectroscopy (FTIR) spectra indicated remarkable changes in the chemical composition and macromolecular conformation of beta-casein after enzymatic hydrolysis. Differential scanning calorimetry (DSC) analysis indicated that the corresponding hydrolysates had higher thermal stability. The enzymatic hydrolysis also led to an increase in the free sulfhydryl content of beta-casein hydrolysates compared with raw beta-casein, which led to the increase in the antioxidant activity of beta-casein hydrolysates.