Zhengwu Wang

Isolation and characterisation of sericin antifreeze peptides and molecular dynamics modelling of their ice-binding interaction.

This study aimed to isolate and characterise a novel sericin antifreeze peptide and investigate its ice-binding molecular mechanism. The thermal hysteresis activity of ice-binding sericin peptides (I-SP) was measured and their activity reached as high as 0.94 °C. A P4 fraction, with high hypothermia protective activity and inhibition activity of ice recrystallisation, was obtained from I-SP, and a purified sericin peptide, named SM-AFP, with the sequence of TTSPTNVSTT and a molecular weight of 1009.50 Da was then isolated from the P4 fraction. Treatment of Lactobacillus delbrueckii Subsp. bulgaricus LB340 LYO with 100 μg/ml synthetic SM-AFP led to 1.4-fold increased survival (p < 0.05). Finally, an SM-AFP/ice binding model was constructed and results of molecular dynamics simulation suggested that the binding of SM-AFP with ice and prevention of ice crystal growth could be attributed to hydrogen bond formation, hydrophobic interaction and non-bond interactions. Sericin peptides could be developed into beneficial cryoprotectants and used in frozen food processing.

Rapid Determination of Fat, Protein and Amino Acid Content in Coix Seed Using Near-Infrared Spectroscopy Technique

The feasibility of near-infrared (NIR) spectroscopy to determine fat, protein, and amino acids (AAs) in Coix seed was investigated. Partial least squares (PLS) regression was applied to establish quantitative model. Competitive adaptive reweighted sampling (CARS) and Norris derivative smoothing (NDS) were used to improve the model accuracy. For fat, protein, Asx, threonine, serine, Glx, alanine, leucine, proline, lysine, and histidine, NDS pretreatment improved the models’ performance and yielded better prediction results. Then, key variables were selected by CARS, and the PLS models could obtain the optimal results with good predictive ability and robustness. The models of protein, Asx, serine, Glx, alanine, valine, isoleucine, leucine, phenylalanine, and proline were fit for screening with the residual predictive deviation (RPD, the ratio between the standard deviation of the reference value and the root mean square error of prediction of the validation set) equal or greater than 2.50. The RPDs of fat and threonine were 1.61 and 2.00, and the other AAs’ were less than 1.50. It was concluded that the NIR spectral technique was suitable for determining fat, protein, and most of AAs in Coix seed. The technique might also give a rough estimate of the contents of glycine, cysteine, methionine, tyrosine, arginine, lysine, and histidine.

The effect of temperature on the physicochemical properties and lamellar structure of canna starch subjected to enzymatic degradation

Canna starch was degraded thermally and enzymatically with or without α-amylase (Bacillus subtilis) at increasing temperatures (50–60 °C). Considerable disruption of the starch granules was found in enzymatically degraded canna starch (EDCS) compared to native canna starch (NCS), while only some swollen starch granules were observed in thermally degraded canna starch (TDCS) even at the critical gelatinization temperature (60 °C). With respect to physicochemical properties, both thermal and enzymatic degradation reduced the swelling power (SP) due to the internal rearrangements within the starch granules. Increased temperature narrows the gelatinization range of canna starch subjected to thermal and enzymatic degradation, however these treatments have different effects on the enthalpy. Small angle X-ray scattering (SAXS) investigation reveals that the lamellar order becomes less pronounced with enhanced temperature, both in TDCS and EDCS, however, a reduced ΔL from the correlation function indicates that the lamellar thickness distribution of TDCS and EDCS are narrower than their native counterpart.

Application of two-phase lamellar model to study the ultrastructure of annealed canna starch: A comparison with linear correlation function

Canna starch was annealed at sub-gelatinization temperature (50°C) with different annealing time. Small angle X-ray scattering (SAXS) was used to estimate the ultrastructure of the annealed starches with the combined two-phase lamellar model and one-dimensional correlation function. The results showed that, upon annealing, water preferably swelled the amorphous regions of canna starch granules while maintained the part of crystalline region, resulted in an increase in amorphous thickness (da) and lamellar repeat distance (d). Power law plots indicates that a mass fractal (self-similar) structure was observed in canna starch, and annealing induces a less compact structure compared to native canna starch (NCS). Correlation analysis showed that no correlation was existed between annealing time and lamellar peak area, width of peak, and volume crystallinity. However, due to the initial degradation of the amorphous region, the volume crystallinity increased significantly with the increase of crystalline thickness (dc).

Study on structural and spectral properties of isobavachalcone and 4-hydroxyderricin by computational method

Isobavachalcone and 4-hydroxyderricin, two major chalcone constituents isolated from the roots of Angelica keiskei KOIDZUMI, exhibit numerous biological activities. Quantum chemical methods have been employed to investigate their structural and spectral properties. The ground state structures were optimized using density functional B3LYP method with 6-311G (d, p) basis set in both gas and solvent phases. Based on the optimized geometries, the harmonic vibrational frequency, the (1)H and (13)C nuclear magnetic resonance (NMR) chemical shift using the GIAO method were calculated at the same level of theory, with the aim of verifying the experimental values. Results reveal that B3LYP has been a good method to study their vibrational spectroscopic and NMR spectral properties of the two chalcones. The electronic absorption spectra were calculated using the time-dependent density functional theory (TDDFT) method. The solvent polarity effects were considered and calculated using the polarizable continuum model (PCM). Results also show that substitutions of different electron donating groups can alter the absorption properties and shift the spectra to a higher wavelength region.