Integrated Evaluation of Dual-Functional DPP-IV and ACE Inhibitory Effects of Peptides Derived from Sericin Hydrolysis and Their Stabilities during In Vitro-Simulated Gastrointestinal and Plasmin Digestions.

Sericin, a byproduct of the silk industry, is an underutilized protein derived from the yellow silk cocoon. This research aimed to produce and characterize the bioactive peptides from sericin using various enzymatic hydrolysis methods. Alcalase, papain, neutrase, and protease were tested under their respective digestion conditions. Among the enzymes tested, neutrase-catalyzed sericin into specific peptides with the strongest dipeptidyl peptidase IV (DPP-IV) and angiotensin-converting enzyme (ACE) inhibitory properties. The peptides were subjected to a simulated in vitro gastrointestinal (GI) digestion in order to determine their stability. The GI peptides that were produced by neutrase hydrolysis continued to have the highest DPP-IV and ACE inhibitory activities. The neutrase -digested peptides were then fractionated via ultrafiltration; the peptide fraction with a molecular weight <3 kDa (UF3) inhibited DPP-IV and ACE activities. After being subjected to in vitro blood plasma hydrolysis, the UF3 was slightly degraded but retained its bioactivity. As a result of these findings, sericin peptides can be utilized as novel dietary ingredients that may alleviate some metabolic syndromes via the dual inhibitory properties of DPP-IV and ACE.

Gelation and vibrational spectroscopy of tropical surimi induced by ascorbic acid and hydrogen peroxide.

The combined effect of ascorbic acid (AsA) and hydrogen peroxide (H2 O2 ) on gel-forming ability and structural changes of lizardfish (LZ) and threadfin bream (TB) surimi were investigated. Addition of 0.15% AsA and 0.1% H2 O2 greatly increased breaking force and distance of LZ surimi by 300% and 55%, respectively. Combination of 0.2% AsA and 0.15% H2 O2 resulted in the maximum TB surimi gel improvement with 150% and 90% increase in breaking force and distance, respectively. Browning reaction obviously occurred when combined AsA and H2 O2 was added, due to ascorbic acid oxidation. Polymerization of myosin heavy chain via disulfide bonds was promoted, and the formation of disulfide bonds was involved through oxidation of sulfhydryl groups with increasing AsA and H2 O2 . Fourier-transform infrared (FT-IR) spectroscopy revealed a decrease in α-helix and an increase in ß-sheet content as AsA and H2 O2 increased in both species. A decrease of band area of aliphatic (2,800 to 3,000 and 1,450 cm-1 ), aromatic (1,208, 757, and ratio 850/830 cm-1 ), and change of disulfide bonds (525 and 540 cm-1 ) suggested an increase in hydrophobic interactions and disulfide bonds with addition of these additives. Based on principal component analysis (PCA), textural characteristics were positively correlated with ß-sheet content. Our study suggested that combination of AsA and H2 O2 greatly enhanced gelation of LZ and TB by increasing not only disulfide bonds but also hydrophobic interactions. PRACTICAL APPLICATION: The combined ascorbic acid and hydrogen peroxide can be used to improve gelation of two important tropical surimi species, namely threadfin bream and lizardfish surimi, without requirement of setting. The optimum concentration of each additive varied with fish species.