Low frequency magnetic field plus high pH promote the quality of pork myofibrillar protein gel: A novel study combined with low field NMR and Raman spectroscopy

Impact of the magnetic field-assisted freezing on the moisture content, water migration degree, microstructure, fractal dimension, and the quality of the frozen tilapia

In this study, we determined the effect of a magnetic field applied during refrigeration in improving the quality of frozen tilapia. Alternating magnetic fields of 10 G, 20 G, 30 G, 40 G, and 50 G were applied during a low-temperature freezing treatment on the back, abdomen, and tail of tilapia. The control group was set at 0 G. A correlation analysis for the fish films after treating with different magnetic field strengths was carried out. The results showed that when the magnetic field was applied to assist freezing, the frozen quality of the tilapia was significantly improved, and the water separation and residual damage were reduced. The felled muscle tissue decreased, the fractal dimension value increased, the hardness decreased, and the elasticity increased. However, the impact of the magnetic field on the quality of the frozen tilapia did not change with an increase in the magnetic field strength. The effect on the back samples was more prominent when the fish were exposed to the magnetic field strength of 40 or 50 G. A magnetic field strength of 50 G was the most effective for the abdominal and tail samples. However, no significant difference was observed in the groups exposed to 10 and 20 G of magnetic fields.

A Relation between Exopolysaccharide from Lactic Acid Bacteria and Properties of Fermentation Induced Soybean Protein Gels

Exopolysaccharide (EPS) producing lactic acid bacteria (LAB) is considered to be an effective texture improver. The effect of LAB strains (different EPS production capacity) on physicochemical properties (texture profile, water distribution, rheological properties, and microstructure), protein conformation, and chemical forces of soybean protein gel was investigated. Correlations between EPS yield and gel properties were established. Large masses of EPS were isolated from L. casei fermentation gel (L. casei-G, 677.01 ± 19.82 mg/kg). Gel with the highest hardness (319.74 ± 9.98 g) and water holding capacity (WHC, 87.74 ± 2.00%) was also formed with L. casei. The conversion of β-sheet to α-helix, the increased hydrophobic interaction and ionic bond helped to form an ordered gel network. The yield was positively correlated with hardness, WHC, A₂₂, viscoelasticity, and viscosity, but negatively correlated with A₂₃ (p < 0.05). The macromolecular properties of EPS (especially the yield) and its incompatibility with proteins could be explained as the main reason for improving gel properties. In conclusion, the EPS producing LAB, especially L. casei used in our study, is the best ordinary coagulate replacement in soybean-based products.

Multi-frequency ultrasound:A potential method to improve the effects of surface decontamination and structural characteristics on large yellow croaker (Pseudosciaena crocea) during refrigerated storage

The effects of multi-frequency ultrasound on surface decontamination and structural characteristics of large yellow croaker (Pseudosciaena crocea) during refrigerated storage were evaluated. The results of total viable counts (TVCs) and psychrophilic bacteria counts (PBCs) demonstrated that multi-frequency ultrasound retarded the growth of microorganisms. The bacteriostatic effect was positively correlated with the increase of ultrasound frequencies. However, compared with triple-frequency ultrasound (TUS, 20/28/40 kHz) treatment, dual-frequency ultrasound (DUS, 20/28 kHz) treatment had higher water-holding capacity (WHC) and immobilized water content, better texture characteristics, lower pH and total volatile basic nitrogen (TVB-N). Through the results of myofibrillar fragmentation index (MFI), intrinsic fluorescence intensity (IFI) and atomic force microscope (AFM), multi-frequency ultrasound could effectively stabilize the myofibrillar protein structure of refrigerated large yellow croaker, which could maintain better texture characteristics. The effects of DUS were the most significant. Therefore, multi-frequency ultrasound treatment could inhibit the growth of microorganisms and improve the structural characteristics of large yellow croaker during refrigerated storage.

Effect of sarcoplasmic proteins oxidation on the gel properties of myofibrillar proteins from pork muscles

This study investigated the influence of sarcoplasmic proteins (SPs) treated by the oxidation system (0.1 mmol/L FeCl₃ , 0.1 mmol/L ascorbic acid, and 0, 1, 5, 10 mmol/L H₂ O₂ ) on the properties of pork myofibrillar proteins (MPs) gel. After oxidation treatment, the SPs showed an increased in carbonyl content and a decreased in total sulfhydryl content, coupled with the cross-linking of protein components by disulfide bonds and covalent bonds. The MPs gel with SPs oxidized at 1 mmol/L H₂ O₂ exhibited the maximal strength while the minimal water holding capacity (WHC). The WHC of MPs gel was significantly decreased with increasing SPs oxidation, leading to the increase of free water and the decrease of immobilized water in the gel system. The microstructures of MPs gels with moderately (1 mmol/L H₂ O₂ ) oxidized SPs showed a more compact and smaller pore gel network than MPs alone, suggesting adding oxidized SPs can expel water trapped in the gel. Furthermore, the environmental polarity of aliphatic C-H groups increased with SPs oxidation.

Acid/alkali shifting of Mesona chinensis polysaccharide-whey protein isolate gels: Characterization and formation mechanism

In this study, structural characteristics and formation mechanism of Mesona chinensis polysaccharide (MCP)-whey protein isolate (WPI) gels including group and molecular changes, intermolecular forces, crystallinity, and moisture migration were investigated under pH shifting conditions. Results showed that MCP and WPI formed a stable gel at pH 10. The free sulfhydryl groups and surface hydrophobicity of the MCP-WPI gels increased with the increasing pH. Hydrophobic and hydrogen bond interactions were the main molecular forces involved in the MCP-WPI gels, and electrostatic interactions and disulfide bonds played a complementary role. The pH conditions evidently influenced the secondary conformational structure of MCP-WPI gels. Molecular weight and X-ray diffraction (XRD) analysis indicated the formation of a hypocrystalline complex with molecular interaction. In addition, low-field magnetometry (LF-NMR) results showed that the T₂ values decreased with increasing pH, indicating that water and gel matrix had the highest interactions at pH 10.

Radio frequency heating improves water retention of pork myofibrillar protein gel: An analysis from water distribution and structure

This study was to explore effects of hot air assisted or not assisted radio frequency (RF, 27.12 MHz, 1.4 kW) heating with different electrode gaps (100 mm, 120 mm, and 140 mm) on the water-holding capacity (WHC) of myofibrillar protein (MP) gel and to understand the underlying mechanism through chemical forces, water distribution, and structure. The results showed that the MP gels heated by RF (100 mm) had the highest WHC and uniform gel network structure. As for RF with 100 mm electrode gap, the increased ionic and hydrogen bonds might be conducive to the WHC compared to water bath heating, which was verified by Low-field nuclear magnetic resonance results that the free water converted into the immobilized water. Raman spectroscopy results revealed that RF (100 mm) induced the self-assembly of β-sheet to α-helix, which conduced to the stable and ordered gel network structure.

Inhibiting effect of ice structuring protein on the decreased gelling properties of protein from quick-frozen pork patty subjected to frozen storage

The effect of ice structuring protein (ISP) on the gelling properties of myofibrillar protein from quick-frozen pork patty during frozen storage was investigated by determining and comparing protein solubility, turbidity and gel properties. Protein solubility was increased by 10.23% and turbidity was decreased after ISP treated. The gel whiteness and strength of myofibrillar protein from patty with ISP were 8.38% and 13.70% higher than that of the control after frozen for 180 days. And the addition of ISP could weaken the influence of frozen storage on water mobility and reduce the water loss. Furthermore, ISP retrained the decrease in the maximum elastic (G') value and loss factor (tan δ) value of samples. Through observing by scanning electron microscope (SEM), ISP retarded the destruction of gel microstructure and maintained the relatively complete tissue of gel. These findings confirmed the importance of ISP in myofibrillar protein gel quality assurance of pork patty during frozen storage.

Development of soy protein isolate/κ-carrageenan composite hydrogels as a delivery system for hydrophilic compounds: Monascus yellow

The aim of the present study was to develop soy protein isolate (SPI) and κ-carrageenan (KC) composite hydrogels as a delivery system for hydrophilic compounds. The pigment of monascus yellow was used as a model. A systematic study was performed to characterize the rheological, textural, microstructural properties and in vitro digestion release profile of monascus yellow of the composite gels. The results of power law modeling, electrophoresis patterns and fourier transform infrared spectroscopy (FTIR) confirmed that non-covalent interactions were involved in the formation of SPI/KC composite hydrogels. Compared to pure κ-carrageenan hydrogels, the incorporation of SPI could promote the formation of tougher, more uniform and compact composite gels with sustained-release property. In addition, the release behaviors of monascus yellow entrapped in the hydrogel network can be well described by the Ritger-Peppas mathematical model. Overall, our study provided a promising strategy to enhance the sustained release performance of hydrogels in digestive conditions.