Zhongjiang Wang

Relationship between Secondary Structure and Surface Hydrophobicity of Soybean Protein Isolate Subjected to Heat Treatment

This study investigated relationship between secondary structure and surface hydrophobicity of soy protein isolate (SPI) subjected to a thermal treatment at 70~90°C. Heat denaturation increased the surface hydrophobicity and surface hydrophobicity decreased as aggregate formed. Heat caused an increase in the relative amount of α-helix structures and an overall decrease in the amount of β-sheet structures when compared with nontreated SPI. The relative amounts of secondary structures varied with time, temperature, and intensity of heat treatment applied. The β-sheet structure was most important for its significant role in denaturation of 7S globulin and following formed aggregates and even in denaturation of 11S globulin. The amount of β-sheet structure in SPI had an inverse correlation with the surface hydrophobicity when the temperature was kept below 90°C. Besides, β-turn structure increased as β-7S/B-11S aggregate formated.

Effects of ultrasound pre-treatment on the structure of β-conglycinin and glycinin and the antioxidant activity of their hydrolysates

The effect of power, time and temperature of ultrasound on the structure of β-conglycinin (7S) and glycinin (11S), and on the antioxidant activity of their hydrolysates were investigated. All ultrasound treated 7S and 11S fractions showed an increase in the α-helix and β-turn proportions, and a decrease in β-sheet and random coil proportions. The polarity of 7S and 11S microenvironment increased after ultrasound treatment. Ultrasound treatment significantly increased the reduction capacity and iron chelating capacity of 7S and 11S hydrolysates. The degree of hydrolysis and free SH groups of 7S and 11S hydrolysates increased after ultrasound pre-treatment. The relative content of high molecular weight peptides reduced, and the relative content of low molecular weight peptides increased in ultrasound treated 7S and 11S hydrolysates. The ultrasonication exposed certain groups of 7S and 11S fractions, improved contact with enzymes, and increased the content of highly active soybean antioxidant peptides.

Differential scanning calorimetry study--assessing the influence of composition of vegetable oils on oxidation.

The thermal oxidation of eight different vegetable oils was studied using differential scanning calorimetry (DSC) under non-isothermal conditions at five different heating rates (5, 7.5, 10, 12.5, and 15°C/min), in a temperature range of 100-400°C. For all oils, the activation energy (Ea) values at Tp were smaller than that at Ts and Ton. Among all the oils, refined palm oil (RPO) exhibited the highest Ea values, 126.06kJ/mol at Ts, 134.7kJ/mol at Ton, and 91.88kJ/mol at Tp. The Ea and reaction rate constant (k) values at Ts, Ton, and Tp were further correlated with oil compositions (fatty acids and triacylglycerols) using Pearson correlation analysis. The rate constant (k) and Ea of all oils exhibited varying correlations with FAs and TAGs, indicating that the thermal oxidation behaviors were affected by oil compositions.

Genetic epistasis analysis of 10 peroxisome proliferator-activated receptor γ-correlated genes in broiler lines divergently selected for abdominal fat content

Chicken peroxisome proliferator-activated receptor γ (PPARγ), which is highly expressed in adipose tissues, is a key factor in fat accumulation in the abdominal fat pad. In this study, association and pairwise epistasis analyses were performed for all the polymorphisms detected in PPARγ and for 9 genes from PPARγ-correlated lipid metabolic pathways for abdominal fat weight (AFW) in 10th-generation populations of Northeast Agricultural University broiler lines divergently selected for abdominal fat content. Epistatic networks were then reconstructed with the identified epistatic effects. Single-marker association analyses showed that 5 of the 20 screened polymorphisms were significantly associated with AFW (P < 0.05), and CCAAT/enhancer-binding protein α (C/EBPα) c.552G>A was 1 of the 5 significant loci. Pairwise interaction analyses showed that 15 pairs of polymorphisms reached a significance level of P < 2.64 × 10(-4) (adjusted by Bonferroni correction) in the lean line, 41 pairs reached significance in the fat line, and 7 pairs reached significance in both lines. Interestingly, many other loci interacted with C/EBPα c.552G>A in both lines. In epistatic network analyses, C/EBPα c.552G>A seemed to behave as a hub for the epistatic network in both lines. All these results revealed that the genetic architecture of C/EBPα c.552G>A for AFW seemed to be an apparent individual main-effect QTL but that it could be dissected into a genetic epistatic network. Our results suggest that C/EBPα c.552G>A might be the most important locus contributing to phenotypic variation in AFW among all the polymorphisms detected in this study.

Relationship Between Surface Hydrophobicity and Structure of Soy Protein Isolate Subjected to Different Ionic Strength

The impact of ionic strength on surface hydrophobicity, solubility, and spatial structure of soy protein isolate were investigated in this article. Surface hydrophobicity was found to be negatively correlated with its solubility as ionic strength increased. The changes in spatial structure of soy protein isolate accounted for the increased surface hydrophobicity caused by ionic strength. Specifically, changes in secondary structures by increased ionic strength were mainly reflected in the increased random coil and decreased α-helices content, which suggested that ionic effects may loosen the protein structures and result in the modification of surface amino acid distribution. This is further verified by the shifted λmax in fluorescence spectra of tryptophan and relative high I850/I830 value in Raman spectra, which was an indicator of the exposure degree of tyrosine residues on the surface of the protein. In addition, the changes in vibration modes of disulfide bonds reflected by Raman spectra also support the impact of saline on the surface hydrophobicity and structure of soy protein isolate. It is believed that these findings could be helpful to understand the impact of salinity on the surface hydrophobicity of soy protein isolate as well as to predict the other functional characteristics of soy protein isolate in system.

Structural Changes in Rice Bran Protein upon Different Extrusion Temperatures: A Raman Spectroscopy Study

Raman spectroscopy is critically evaluated to establish the limits to which it may be used to detect changes in protein conformation upon extrusion. Rice bran protein (RBP) extruded with different temperatures (100, 120, 140, and 160°C, labeled as ERBP-) was considered. DSC showed that extrusion at 100°C increased of RBP but decreased its , while, after extrusion treatment at 120°C, RBP completely denatured. A progressive increase in unordered structure and a general decrease in α-helix structure and β-sheet structure of extruded RBP were observed from Raman study. Meanwhile the content of unordered structure increased up to 140°C and then decreased at 160°C, while the trend of α-helix and β-sheet content was opposite, which was contributed to the composite effect of formation of some more protein aggregation and protein denaturation. Extrusion generally induced a significant decrease in Trp band near 760 cm−1 but an increase at 160°C. No significant difference was observed in Tyr doublet ratios between controlled RBP samples and extruded RBP below 160°C, whereas Tyr doublet ratios of extruded RBP decreased at 160°C. Intensity of the band assigned to bending decreased progressively and then increased as extrusion temperature increased, indicating changes in microenvironment and polarity.

Effect of ultrasound treatment on the wet heating Maillard reaction between mung bean [Vigna radiate (L.)] protein isolates and glucose and on structural and physico‐chemical properties of conjugates

BACKGROUND The objective of this study was to determine the effect of ultrasound treatment on the wet heating Maillard reaction between mung bean protein isolates (MBPIs) and glucose, and on structural and physico-chemical properties of the conjugates. RESULTS The degree of glycosylation of MBPI-glucose conjugates treated by ultrasound treatment and wet heating (MBPI-GUH) was higher than that of MBPI-glucose conjugates only treated by wet heating (MBPI-GH). Solubility, emulsification activity, emulsification stability and surface hydrophobicity of MBPI-GUH were higher than that of MBPI-GH. Grafted MBPIs had a lower content of α-helix and unordered coil, but a higher content of β-sheet and β-turn structure than MBPIs. No significant structural changes were observed in β-turn and random coil structure of MBPI-GUH, while α-helix content increased with ultrasonic time, and decreased at 300 W ultrasonic power with the increase of β-sheet. MBPI-GUH had a less compact tertiary structure compared to MBPI-GH and MBPI. Grafting MBPIs with glucose formed conjugates of higher molecular weight, while no significant changes were observed in electrophoresis profiles of MBPI-GUH. CONCLUSION Ultrasound-assisted wet heating Maillard reaction between MBPIs and glucose could be a promising way to improve functional properties of MBPIs.

Effect of the interaction between myofibrillar protein and heat-induced soy protein isolates on gel properties

The effect of the interaction between myofibrillar protein (MP) and heat-induced soy protein isolates (SPI) on gel properties was examined. To enhance the interaction between MP and SPI, SPI was subjected to thermal treatments at 60, 80, and 95 °C. The results showed that hydrophobic interactions played the most important role in MP-heated SPI (HSPI) gels. Hydrogen bonds played an important role in stabilizing the mixed gels, but this decreased with increasing heat treatment temperature of SPI. Disulfide bonds were not a significant force stabilizing the mixed gels. The gel properties of HSPI-MP were enhanced significantly (P < 0.05) by the inclusion of preheated SPI (95 °C, 30 min), including hardness, springiness, and water-holding capacity (WHC). Dynamic rheological analysis showed that heat treatment decreased the onset temperature of mixed gels and significantly increased the final G’. Notable cross-linked strands formed in MP-HSPI (80 °C) and MP-HSPI (95 °C) gels, while the smoothest and most ordered gel network structure was observed in the MP-HSPI (95 °C) gel.

Secondary Structure and Subunit Composition of Soy Protein In Vitro Digested by Pepsin and Its Relation with Digestibility.

In the present study, in vitro digestibility and structure of soybean protein isolates (SPIs) prepared from five soybean varieties were investigated in simulated gastric fluid (SGF), using FT-IR microspectroscopy and SDS-PAGE. The result indicated that β-conformations were prone to be hydrolyzed by pepsin preferentially and transformed to unordered structure during in vitro digestion, followed by the digestion of α-helix and unordered structure. A negative linear correlation coefficient was found between the β-conformation contents of five SPIs and their in vitro digestibility values. The intensities of the protein bands corresponding to 7S and 11S fractions were decreased and many peptide bands appeared at 11~15 kDa during enzymatic hydrolysis. β-conglycinin was poorly hydrolyzed with pepsin, especially the β-7S subunit. On the other hand, basic polypeptides of glycinin degraded slower than acidic polypeptides and represented a large proportion of the residual protein after digestion. 11S-A3 of all SPIs disappeared after 1 h digestion. Moreover, a significant negative linear correlation coefficient (r = −0.89) was found between the β-7S contents of five SPIs and their in vitro digestibility values. These results are useful for further studies of the functional properties and bioactive properties of these varieties and laid theoretical foundations for the development of the specific functional soy protein isolate.

Structural and functional properties of rice bran protein oxidized by peroxyl radicals

ABSTRACT The structure and functionalities of rice bran protein (RBP) oxidized by peroxyl radicals were analyzed in this study. The thermal decomposition of 2,2′-azobis [2-amidinopropane] dihydrochloride (AAPH) was used to generate peroxyl radicals. Increased oxidation of RBP by AAPH gradually generated more carbonyl (COOH) groups, which resulted in a loss of protein sulfhydryl groups. Low oxidization (≤0.2 mmol/L AAPH) could cause structural unfolding with an increase in surface hydrophobicity and emulsion properties but reducing the solubility and disulfide bonding. Moderate and high oxidization (>0.2 mmol/L AAPH) could result in soluble aggregates formed by subunits with molecular weights of 53, 49, and 36 kDa, attributed to globulin, albumin, and glutelin, increasing the solubility and disulfide bonding but decreasing the surface hydrophobicity and emulsion stability. Oxidization by low concentration AAPH induced a more unordered structure and transformation from β-turn to β-sheets, while a more ordered structure increased with aggregation.