Xiaonan Sui

Ultrasound-assisted aqueous enzymatic extraction of oil from perilla (Perilla frutescens L.) seeds

In the present study the effects of ultrasonic pretreatment and the types of enzyme on oil yield were investigated. The optimum ultrasonic pretreatment parameters were found to be 250 W of ultrasonic power, 30 min of ultrasonic time, and 50°C of ultrasonic temperature. Five types of enzyme, Cellulase, Viscozyme L, Alcalase 2.4L, Protex 6L, and Protex 7L, were evaluated for their effectiveness in releasing oil from ultrasonic pretreated perilla seeds. The highest oil yield of 81.74% was observed in cellulase treated perilla seed samples. The physicochemical properties of the control, hexane, and enzyme extracted perilla seed oils were compared. No significant (P > 0.05) differences were observed in iodine value, refractive index, unsaponifiable matter, saponification value, peroxide value, and acid value.

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.

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.

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.

Functional and conformational changes to soy proteins accompanying anthocyanins: Focus on covalent and non-covalent interactions

The present study was aimed to evaluate the interaction between anthocyanins from black rice and soybean protein isolate (SPI) via non-covalent and covalent bindings and the impact of these interactions on the functional and conformational changes of soybean protein. The conformational changes of the protein structure with different concentrations of anthocyanins (0.05, 0.1%, and 0.2%) were analyzed using three-dimensional fluorescence and Fourier transform infrared spectroscopy. The anthocyanins were more likely to form covalent interactions with SPI instead of non-covalent interactions. The addition of anthocyanins changed the secondary structure of SPI with a decrease in β-sheets and an increase in β-turns and random coils. The emulsifying and foaming properties of SPI were improved after complexation with anthocyanins. This study might be useful for elucidating the mechanisms behind the binding of anthocyanins with SPI and the possible uses of SPI-anthocyanin complexes in food formulations.

Heating Quality and Stability of Aqueous Enzymatic Extraction of Fatty Acid-Balanced Oil in Comparison with Other Blended Oils

The heating performance of enzyme-assisted aqueous processing-extracted blended oil (EAEPO), hexane-extracted blended oil (HEBO), and three kinds of blended oils was investigated by varying the heating times. Oil degradation was monitored by analysis of the acid value (AV), peroxide value (PV), p-anisidine value (p-AV), color, and trans-fatty acid composition. The fatty acid ratios of EAEPO, HEBO, and the three kinds of blended oils were very similar (0.27 : 1.03 : 0.96, 0.27 : 1.08 : 1.16, 0.27 : 0.65 : 0.8, 0.27 : 0.6 : 0.84, and 0.27 : 0.61 : 0.79, resp.). The AV and color increased in proportion to the heating time for all the oils. There was a rapid increase in the PV and p-AV of EAEPO and HEBO after heating for only 1 h, whereas the other three blended oils showed a rapid increase after heating for 2 h or 6 h. Despite the highest trans-fatty acid content found for HEBO, this content was relatively low and remained low up to a heating time of 8 h. It was found that after heating, a fatty acid ratio relatively close to its ideal value (0.27 : 0.48 : 0.49) was maintained by EAEPO, which indicates that EAEPO is tolerant to heat treatment and is suitable for maintaining a healthy diet.

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.

Physical-Chemical Properties of Edible Film Made from Soybean Residue and Citric Acid

The effect of citric acid on the properties of soybean enzyme-assisted aqueous extraction processing (EAEP) residue edible film was studied. The washed soybean EAEP residue was produced by the process of EAEP. It was determined that the washed soybean EAEP residue is rich in fibers (76.10 ± 1.03%) and has lower oil and protein contents (7.74 ± 0.11% and 3.50 ± 0.20%, resp.). Edible films intended for food packaging have been produced from the washed EAEP residue combined with glycerol, different concentrations of citric acid (0%, 10%, 15%, 20%, 25%, and 30%), and sodium hypophosphite. The spectra have evidenced that the cross-linking reaction of citric acid and fibers has taken place in the residue. 30-CA films showed the highest tensile strength (17.52 MPa) and the lowest water vapor permeability (7.21 g·cm−1·s−1·Pa−1). Also, it indicated that citric acid can cross-link with the hydroxyls of polysaccharide and improve the compatibilization between the polymeric molecules to improve the intermolecular interaction between polysaccharide molecules, so that the water uptake is reduced. The smooth surface and better translucency of the films suggest that the EAEP residue films treated with citric acid are suitable for application in food packaging.

Complexation of thermally-denatured soybean protein isolate with anthocyanins and its effect on the protein structure and in vitro digestibility

The complexation of anthocyanin-rich black rice extracts (ARBRE) with soybean protein isolate (SPI) heated at 0, 70, 85, and 100 °C and its effect on protein digestibility were studied. The structural changes of SPI during its interaction with ARBRE in all the samples were studied by Fourier transform infrared, circular dichroism, and fluorescence spectroscopy. The secondary structure changes of SPI in all the samples after complexation with ARBRE showed a significant increase in α-helix and a significant decrease in β-sheet contents. Results also showed that ARBRE quenched the SPI fluorescence (in both unheated and heated samples) via static quenching with a single binding site. The digestibility of unheated and heated SPI was improved upon complexing with ARBRE. The formation of the SPI-ARBRE complexes is beneficial for the application of soy protein-based products in foods by increasing their protein digestibility and nutritional quality.