Na Sun

Contributions of molecular size, charge distribution, and specific amino acids to the iron-binding capacity of sea cucumber (Stichopus japonicus) ovum hydrolysates

This study investigated the contributions of molecular size, charge distribution and specific amino acids to the iron-binding capacity of sea cucumber (Stichopus japonicus) ovum hydrolysates (SCOHs), and further explored their iron-binding sites. It was demonstrated that enzyme type and degree of hydrolysis (DH) significantly influenced the iron-binding capacity of the SCOHs. The SCOHs produced by alcalase at a DH of 25.9% possessed the highest iron-binding capacity at 92.1%. As the hydrolysis time increased, the molecular size of the SCOHs decreased, the negative charges increased, and the hydrophilic amino acids were exposed to the surface, facilitating iron binding. Furthermore, the Fourier transform infrared spectra, combined with amino acid composition analysis, revealed that iron bound to the SCOHs primarily through interactions with carboxyl oxygen of Asp, guanidine nitrogen of Arg or nitrogen atoms in imidazole group of His. The formed SCOHs-iron complexes exhibited a fold and crystal structure with spherical particles.

Characterization of sea cucumber (stichopus japonicus) ovum hydrolysates: calcium chelation, solubility and absorption into intestinal epithelial cells

BACKGROUND Sea cucumber (Stichopus japonicus) ovum hydrolysates (SCOHs) chelated with calcium were produced to investigate the characteristics of calcium binding and solubility, as well as to study any effects on calcium absorption by human intestinal epithelial cells. RESULTS The results of the present study show that the calcium-binding capacity of SCOHs depended greatly on the type of proteases. The maximum level of Ca binding (0.38 mmol L-1 ) occurred when trypsin was used, with a peptide yield of 85.7%. Investigation of the possible chelating modes between SCOHs and calcium ions indicated that calcium ions bound to SCOHs primarily via interactions with carboxyl oxygen and amino nitrogen atoms of Glu and Asp and also that the phosphoserine residues might be also responsible for SCOH-calcium chelation. Moreover, SCOH-calcium complexes maintained the solubility of calcium under simulated gastrointestinal digestion, regardless of the presence of dietary components such as oxalate. Furthermore, SCOH-Ca led to higher peak intracellular [Ca2+ ]i in both Caco-2 cells (338.3 nmol L-1 versus 269.6 nmol L-1 ) and HT-29 cells (373.9 nmol L-1 versus 271.7 nmol L-1 ) than casein phosphopeptide-Ca. CONCLUSION Carboxyl oxygen and amino nitrogen atoms in the SCOHs could bind calcium ions, forming SCOH-calcium complexes. These complexes improved calcium solubility under simulated gastrointestinal digestion and also promoted calcium absorption in Caco-2 and HT-29 cells.

An Exploration of the Calcium-Binding Mode of Egg White Peptide, Asp-His-Thr-Lys-Glu, and in vitro Calcium Absorption Studies of Peptide-Calcium Complex

The binding mode between the pentapeptide (DHTKE) from egg white hydrolysates and calcium ions was elucidated upon its structural and thermodynamics characteristics. The present study demonstrated that the DHTKE peptide could spontaneously bind calcium with a 1:1 stoichiometry, and that the calcium-binding site corresponded to the carboxyl oxygen, amino nitrogen, and imidazole nitrogen atoms of the DHTKE peptide. Moreover, the effect of the DHTKE-calcium complex on improving the calcium absorption was investigated in vitro using Caco-2 cells. Results showed that the DHTKE-calcium complex could facilitate the calcium influx into the cytosol and further improve calcium absorption across Caco-2 cell monolayers by more than 7 times when compared to calcium-free control. This study facilitates the understanding about the binding mechanism between peptides and calcium ions as well as suggests a potential application of egg white peptides as nutraceuticals to improve calcium absorption.

Enzyme-controlled hygroscopicity and proton dynamics in sea cucumber (Stichopus japonicus) ovum peptide powders

The enzyme-controlled hygroscopicity of peptide powders during storage at room temperature may have a profound effect on their properties. The present study aims to elucidate hygroscopicity, proton dynamics, as well as effect on the microstructure of sea cucumber ovum peptides (SCOPs) powder produced with different enzymes during storage. The SCOPs produced with Alcalase exhibited the strongest moisture absorption capacity, which was significantly higher than those of SCOPs produced with papain, neutrase, and trypsin (P < .05). This might be attributed to the greater hydrolysis of Alcalase and producing more polar groups. Moreover, the proton dynamic and the transformations of water populations varied greatly among the SCOPs with different enzymes. Even so, the SCOPs exhibited a common water migration rule that free water was gradually transformed into immobilized water that was simultaneously converted into bound water after moisture absorption. The hygroscopicity induced morphological changes of SCOPs, which was converted from a smooth amorphous structure into different sizes of particle agglomerates. Moreover, the SCOPs produced with Alcalase displayed more and smaller agglomerates than those produced with papain, neutrase, and trypsin. This study provides a theoretical basis for quality assurance of peptide powders, particularly those produced with Alcalase.

Kinetics of Antioxidant-Producing Maillard Reaction in the Mixture of Ribose and Sea Cucumber (Stichopus japonicus) Gut Hydrolysates

ABSTRACT Maillard reaction products (MRPs) were produced in sea cucumber gut hydrolysates (SCGHs)-ribose system at 75°C, 85°C, and 95°C with a pH value of 7.0 or 8.0 for 12 hour. The parameters of amount of intermediate products, fluorescence intensity, browning development, and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging ability showed a positive correlation with each other in SCGHs-ribose system. The amount of intermediate products, fluorescence intensity, and browning development followed the zero-order kinetic with activation energy from 62 to 91 kJ/mol in the Maillard reaction of SCGHs-ribose system. Moreover, 2-methyl-butanal has positive and significant correlation with DPPH radical scavenging ability of SCGHs-ribose MRPs. These results suggest that Maillard reaction improves the antioxidant activity of SCGHs, which contributes to the generation of intermediate, fluorescent, browning, and volatile products of SCGHs-ribose system.

Characterization of proteolysis in muscle tissues of sea cucumber Stichopus japonicus

The proteolysis in muscle tissues of sea cucumber Stichopus japonicus (sjMTs) was characterized. The proteins from sjMTs were primarily myosin heavy chains (MHCs), paramyosin (Pm), and actin (Ac) having a molecular mass of approximately 200, 98, and 42 kDa, respectively. Based on SDS-PAGE analysis and quantification of trichloroacetic acid (TCA)-soluble peptides released, degradation of muscle proteins from sjMTs was favorable at pH 5 and 50°C. Proteolysis of MHCs was mostly inhibited by cysteine protease inhibitors, including trans-epoxysuccinyl-L-leucyl-amido (4-guanidino) butane (E-64) and antipain (AP). E-64 and AP completely inhibited the degradation of Pm and Ac, while iodoacetic acid showed a partially inhibitory effect. These results indicated that the proteolysis of sjMTs was mainly attributed to cysteine proteases. Avoidance of setting the tissues at 40–50°C and slightly acidic condition and inhibition of cysteine proteases are helpful for decreasing sea cucumber autolysis.

The formation pattern of off-flavor compounds induced by water migration during the storage of sea cucumber peptide powders (SCPPs)

The formation pattern of off-flavor compounds induced by water migration in sea cucumber peptide powders (SCPPs) stored at 25 °C and 75% RH for 24 h and 80 days were investigated. Water migration characteristic of SCPPs was monitored by LF-NMR. The effect of water migration on structure and morphology were analyzed by SEM, CD, and FTIR, respectively. The antioxidant activity of SCPPs was detected by EPR. Volatiles generated from SCPPs were detected by P&T-GC-MS. The antioxidant activity of SCPPs declined and structure exhibited abnormalities during the storage. After 24 h of storage, kinds of aldehydes decreased and the content of alcohols increased obviously. After 80 days, (Z)-3,5-dimethyl-2-(1-propenyl)-pyrazine and 1,2-benzenedicarboxylic acid-bis(2-methylpropyl) ester were identified as the characteristic off-flavor. These off-flavor compounds were probably formed through Maillard reaction. esterification, and microbial metabolism. This study can provide a basis for further exploration of the off-flavor formation mechanism.

Formation and evaluation of casein-gum arabic coacervates via pH-dependent complexation using fast acidification

The formation of complex coacervation using fast acidification at 25 °C for 0.5 h between casein (CAS) and gum arabic (GA) was investigated by turbidity, particle size distribution (PSD), zeta potential (ZP), and Fourier transform infrared (FTIR). When the mass ratio of CAS and GA was 1:1 and the total biopolymer concentration (CT) was 0.5% (w/v), an optimum pH (pHopt) of complex coacervation was found at pH 3.5. Particle size distribution (PSD) of homogenous CAS and GA solutions, and mixture solution of CAS-GA at critical pH values revealed the association and disassociation processes during complex coacervation. Meanwhile, ZP and FTIR spectra analyses indicated that the complexation between CAS and GA was ascribed to electrostatic interaction and hydrogen bonding. The CAS-GA coacervates were characterized by X-ray diffraction (XRD), thermogravimetric analyzer (TGA), and differential scanning calorimetry (DSC). Two XRD peaks (2θ = 8° and 23°) differing from CAS and GA indicated the characteristic of CAS-GA coacervates. Moreover, the thermal stability of CAS-GA coacervates was superior to CAS and GA below 220 °C. The good performance of CAS-GA coacervates predicts a bright future in application of food and pharmacy industries.

Targeted regulation of hygroscopicity of soybean antioxidant pentapeptide powder by zinc ions binding to the moisture absorption sites

In the present study, a targeted regulation of hygroscopicity of soybean antioxidant pentapeptide (SAP) powder was explored by zinc ions binding to its moisture absorption sites. Scanning electron microscopy, X-ray diffraction analysis, Fourier transform infrared spectroscopy and an energy-dispersive X-ray spectroscope were used to confirm the formation of the SAP-zinc complex. The results showed that morphology of SAP-zinc complex belonged to crystalline nanoparticles. The moisture sorption/desorption kinetics of the SAP-zinc complex changed compared to that of the SAP. In particular, the moisture sorption capacity of the SAP decreased and the distribution of adsorbed water changed after zinc chelation. Based on the binding of zinc ions to the moisture absorption sites, the hygroscopicity of SAP powder could be target regulated. Thus, this study could provide a new method to regulate the hygroscopicity of peptide powder.