Songyi Lin

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.

Effects of electron beam irradiation on physicochemical properties of corn flour and improvement of the gelatinization inhibition

The properties and viscosity-reduction mechanism of corn flour irradiated by electron beam have not been understood properly. Here, we investigate the effects of electron beam irradiation (EBI) on the gelatinization and physicochemical properties of corn flour irradiated by 0-5.40kGy of electron beam. The total starch and crude fiber contents of corn flour decreased significantly (P<0.05) after EBI treatment, while the moisture and reducing sugar contents increased significantly (P<0.05). EBI caused perforations on the corn flour particle surfaces, and the irradiated parts of the particles would gradually peel off and afford smooth surfaces, spherical structures, and smaller sizes. Molecular chains of corn flour broke owing to EBI. After irradiation, the pasting peak viscosity decreased dramatically (P<0.01) from 1251.74 to 7.16Pa·s, showing that the gelatinization of corn flour was completely inhibited. Thus, EBI can be used to inhibit the gelatinization of corn flour, which may be beneficial for industrial and food formulations.

Water dynamics of Ser-His-Glu-Cys-Asn powder and effects of moisture absorption on its chemical properties

BACKGROUND This study has elucidated moisture dynamics in the soybean peptide, Ser-His-Glu-Cys-Asn (SHECN) powder by using dynamic vapor sorption (DVS) and nuclear magnetic resonance (NMR). We also tried to investigate the effects of moisture absorption on the biological activity and chemical properties of SHECN with some effective methods such as mid-infrared (MIR) spectroscopy and gas chromatography-mass spectrometry (GC-MS). RESULTS DVS results showed that the moisture absorption of SHECN could reach a maximum of 33%, and the SHECN powder after synthesis actually existed in a trihydrate state of SHECN.3H2 O. Low-field NMR revealed that three water proportions including strong combined water, binding water and bulk water were involved in SHECN moisture absorption and absored water dominantly existed in the form of combined water. Magnetic resonance imaging (MRI) and MIR spectroscopy results indicated that moisture absorption could change the morphology and structure of SHECN. After moisture absorption at 50% and 75% relative humidity, 19 volatiles were identified by GC-MS analysis. Additionally, this study showed that a part of reductive groups in SHECN was oxidized and its antioxidant ability declined significantly (P < 0.05) after moisture absorption. CONCLUSION Water absorbed into SHECN powder can significantly change its microstructure and cause its activity to decrease. We must prevent SHECN from absorbing moisture during storage because the water can accelerate the oxidation of samples and promote microbial reactions.

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.

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.

Investigation on complex coacervation between fish skin gelatin from cold-water fish and gum arabic: Phase behavior, thermodynamic, and structural properties

The study is aimed to investigate phase behavior, thermodynamic, and structural properties based on complex coacervation between fish skin gelatin (FSG) from cold-water fish and gum arabic (GA). Phase separation behavior between FSG and GA was investigated as a function of pH through varying mixing ratios from 4:1 to 1:4 at 25 °C and 1.0 wt% of total biopolymer concentration. The turbidity of FSG-GA mixture reached the maximum (1.743) at the 1:2 of mixing ratio and pHopt 3.5, and stabilized at zero. Then physicochemical properties of FSG-GA coacervates at pHopt 3.5 and FSG-GA mixtures at pH 6.0 (>pHc) were evaluated. Scanning electron microscope (SEM) and X-ray diffraction (XRD) showed that the interactions between FSG and GA occurred at pHopt 3.5 and were very weak at pH 6.0 (>pHc). The isothermal titration calorimetry (ITC) results including the negative Gibbs free energy change (ΔG = -18.71 ± 1.300 kJ/mol), binding enthalpy (ΔH = -41.81 ± 1.300 kJ/mol) and binding entropy (TΔS = -23.10 kJ/mol) indicated that the complexation between FSG and GA was spontaneous and driven by negative enthalpy owing to the electrostatic interaction and hydrogen bondings. The zeta potential (ZP) of FSG-GA coacervates at pHopt 3.5 was -9.00 ± 0.79 mV that was not close to electrically neutral, indicating other interactions besides electronic interaction. Hydrogen bondings in FSG-GA mixtures at pH 6.0 and 3.5 were found to be stronger than pure FSG at pH 6.0 and 3.5 owing to that the amide II peaks shifted to high wavenumbers. Electronic interaction was proven to exist in FSG-GA mixtures at pH 6.0 through the vanishment of asymmetric COO- stretching. However, the electronic interaction in FSG-GA coacervates at pHopt 3.5 was obviously stronger than FSG-GA mixtures at pH 6.0, resulting from the vanishment of asymmetric and symmetric COO- stretching vibration and the positively charged FSG and GA. The intrinsic fluorescence represented that the introduction of GA changed the microenvironment of tyrosine residues in FSG, which may be owing to the unfolding of the tertiary conformation. Moreover, the decrease of pH could promote the formation of random coils of FSG through circular dichroism (CD). Therefore the addition of GA into FSG and decrease of pH might enhance the conformation freedom of FSG, which would bring about favorable entropic effects and contribute to the complexation.

Moisture absorption and dynamic flavor changes in hydrolysed and freeze-dried pine nut (Pinus koraiensis) by-products during storage

In the present study, two different fractions of pine nut (Pinus koraiensis) protein hydrolysate powder (PNPHP1-3kDa and PNPHP3-10kDa) were prepared and stored for fifteen days at 25°C and 50% relative humidity. Changes in moisture absorption, secondary structure and flavor compounds were measured at various time intervals over fifteen days. Results showed that the PNPHP3-10kDa had higher moisture absorption capacity from day 6 to day 15 and that the secondary structure of two PNPHP fractions was changed. Major nine and eight flavor compounds were identified from PNPHP1-3kDa and PNPHP3-10kDa, respectively. PNPHP1-3kDa mainly generated aldehydes and PNPHP3-10kDa generated pyrazines. Finally, the formation of pyrazines was conjectured. The data suggests that Maillard reaction, microbial fermentation and lipid oxidation occurred during storage. The reactions appeared to be strongest by the sixth day.