Angiotensin converting enzyme inhibitory peptides released from the hydrolysate of casein and the milk fermented by Lactobacillus casei ADA03

Milk proteins are considered not only a valuable nutrient but also a good source of many bioactive peptides including angiotensin converting enzyme (ACE) inhibitory peptides. ACE, which is a multifunctional enzyme present in the rennin-angiotensin system, has a prominent role in the regulations of blood pressure as well as water and electrolyte balance. ACE elevates blood pressure by generating vasoconstrictor, angiotensin II, in conjunction with inactivating vasodilator, bradykinin. Inhibition of ACE results in antihypertensive effect. The present study was focused on (1) the optimization of the production of ACE inhibitory peptides by modes of hydrolysis of casein with pancreatin and fermentation of milk by Lactobacillus casei ADA03 and (2) on the isolation of such peptides using membrane and liquid chromatographic techniques. Furthermore, characterization of ACE inhibitory peptides was carried out by LC/MS/MS technique. The results indicated that hydrolysate of casein at 37°C for 8 h and milk fermented with Lactobacillus casei ADA03 at 37 °C for 24 h exhibited the highest ACE inhibitory activity when compared within the same mode of production. Ultrafiltration with molecular weight cut-off of 2000 Da membrane and Bio-Gel P2 gel filtration chromatography were the effective methods for the purification of ACE inhibitory peptides. Amino acid sequence analysis of ACE inhibitory peptides by LC/MS/MS revealed (1) the formation of novel ACE inhibitory peptides in either casein hydrolysate or fermented milk and (2) the significance of hydrophobic amino acid at the C-terminal end of such peptides. The ACE inhibitory peptides isolated from this study can be incorporated into food, promoting the opportunity of a food product containing antihypertensive property in the functional food market. In addition, milk fermented with Lactobacillus casei ADA03 can be regarded as a probiotic product with multifunctional properties.