Production of the angiotensin I converting enzyme inhibitory peptides and isolation of four novel peptides from jellyfish (Rhopilema esculentum) protein hydrolysate.

BACKGROUND: Angiotensin I converting enzyme (ACE) plays an important role in regulating blood pressure in the human body. ACE inhibitory peptides derived from food proteins could exert antihypertensive effects without side effects. Jellyfish (Rhopilema esculentum) is an important fishery resource suitable for production of ACE inhibitory peptides. The objective of this study was to optimize the hydrolysis conditions for production of protein hydrolysate from R. esculentum (RPH) with ACE inhibitory activity, and to isolate and identify the ACE inhibitory peptides from RPH. RESULTS: Rhopilema esculentum protein was hydrolyzed with Compound proteinase AQ to produce protein hydrolysate with ACE inhibitory activity, and the hydrolysis conditions were optimized using response surface methodology. The optimum parameters for producing peptides with the highest ACE inhibitory activity were as follows: hydrolysis time 3.90 h, hydrolysis temperature 58 °C, enzyme:substrate ratio 2.8% and pH 7.60. Under these conditions, the ACE inhibitory rate reached 32.21%. In addition, four novel ACE inhibitory peptides were isolated, and their amino acids sequences were identified as Val-Gly-Pro-Tyr, Phe-Thr-Tyr-Val-Pro-Gly, Phe-Thr-Tyr-Val-Pro-Gly-Ala and Phe-Gln-Ala-Val-Trp-Ala-Gly, respectively. The IC50 value of the purified peptides for ACE inhibitory activity was 8.40, 23.42, 21.15 and 19.11 µmol L(-1) . CONCLUSION: These results indicate that the protein hydrolysate prepared from R. esculentum might be a commercial competitive source of ACE inhibitory ingredients to be used in functional foods. © 2015 Society of Chemical Industry.

Oral administration of corn zein hydrolysate stimulates GLP-1 and GIP secretion and improves glucose tolerance in male normal rats and Goto-Kakizaki rats.

We have previously demonstrated that ileal administration of the dietary protein hydrolysate prepared from corn zein (ZeinH) stimulated glucagon-like peptide-1 (GLP-1) secretion and attenuated hyperglycemia in rats. In this study, to examine whether oral administration of ZeinH improves glucose tolerance by stimulating GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) secretion, glucose tolerance tests were performed in normal Sprague-Dawley male rats and diabetic Goto-Kakizaki (GK) male rats. The test solution was gavaged before ip glucose injection in normal rats or gavaged together with glucose in GK rats. Blood samples were collected from the tail vein or by using the jugular catheter to measure glucose, insulin, GLP-1, and GIP levels. In the ip glucose tolerance test, oral administration of ZeinH (2 g/kg) significantly suppressed the glycemic response accompanied by an immediate increase in plasma GLP-1 and GIP levels in normal rats. In contrast, oral administration of another dietary peptide, meat hydrolysate, did not elicit a similar effect. The glucose-lowering effect of ZeinH was attenuated by a GLP-1 receptor antagonist or by a GIP receptor antagonist. Furthermore, oral ZeinH induced GLP-1 secretion and reduced glycemic response in GK rats under the oral glucose tolerance test. These results indicate that the oral administration of the dietary peptide ZeinH improves glucose tolerance in normal and diabetic rats by its incretin-releasing activity, namely, the incretinotropic effect.

Estimation of inhibitory effects of hemicellulosic wood hydrolysate inhibitors on PHA production by Burkholderia cepacia ATCC 17759 using response surface methodology.

Sugar maple hemicellulosic hydrolysate was utilized as a renewable feedstock for polyhydroxyalkanoates production by Burkholderia cepacia ATCC 17759. To estimate inhibitory effects of the hydrolysate, response surface methodology was utilized to analyze cell growth and PHA accumulation in the presence of multiple inhibitors. Mixture design was employed to study the correlation between the proportion of phenolics and total inhibition. The resultant models (R(2) as 92.42% and 93.14% for cell growth and PHA production, respectively) indicated syringic acid was the most inhibitory among three phenolics and synergistic inhibition was observed for the combinations of vanillin/syringic acid and vanillic acid/syringic acid. When furfural, levulinic acid, and acetate were also present during the fermentation, central composite design was employed. The regression model using 48 h cell growth as the response surface (R(2)=87.82%) showed acetate was the most inhibitory. Additionally, strong synergistic effects were observed for the combinations of acetate/phenolics and levulinic acid/furfural.