Effect of freeze–thaw cycles on the emulsion activity and structural characteristics of soy protein isolate

Inhibitive effect of trehalose and sodium pyrophosphate on oxidation and structural changes of myofibrillar proteins in silver carp surimi during frozen storage

This work investigated the cryoprotective effect of trehalose (TH) and sodium pyrophosphate (SPP) alone and in combination on myofibrillar protein (MP) oxidation and structural changes in silver carp surimi during 90 days of frozen storage (-20 °C). TH combined with SPP was significantly more effective than single TH or SPP in preventing MP oxidation (P < 0.05), showing a higher SH content (6.05 nmol/mg protein), and a lower carbonyl (4.24 nmol/mg protein) and dityrosine content (1280 A.U.). SDS-PAGE results indicated that TH combined with SPP did not differ significantly from TH and SPP in inhibiting protein degradation but was more effective in inhibiting protein crosslinking. Moreover, all cryoprotectants could stabilise the secondary and tertiary structures and inhibit unfolded and aggregation of MP, with the combination of TH and SPP being the best. It's worth noting that TH combined with SPP had a synergistic effect on inhibiting the decrease in α-helix content and gel-forming ability, and the increase in surface hydrophobicity. Overall, TH combined with SPP could significantly inhibited MP oxidation and structural changes in surimi during frozen storage and improve the gel-forming ability, which was significantly better than single TH or SPP.

Effects of multi-frequency ultrasound-assisted immersion freezing processing on myofibrillar protein structure and lipid oxidation of large yellow croaker (Larimichthys crocea) during long-time frozen storage

In this study, large yellow croaker (Larimichthys crocea) was frozen using multi-frequency ultrasound-assisted freezing (MUIF) with different powers (160 W, 175 W, and 190 W, respectively) and stored at -18 °C for ten months. The effect of different ultrasound powers on the myofibrillar protein (MP) structures and lipid oxidation of large yellow croaker was investigated. The results showed that MUIF significantly slowed down the oxidation of MP by inhibiting carbonyl formation and maintaining high sulfhydryl contents. These treatments also held a high activity of Ca2+-ATPase in the MP. MUIF maintained a higher ratio of α-helix to β-sheet during frozen storage, thereby protecting the secondary structure of the tissue and stabilizing the tertiary structure. In addition, MUIF inhibited the production of thiobarbituric acid reactive substances value and the loss of unsaturated fatty acid content, indicating that MUIF could better inhibit lipid oxidation of large yellow croaker during long-time frozen storage.

Soy protein isolate-catechin complexes conjugated by pre-heating treatment for enhancing emulsifying properties: Molecular structures and binding mechanisms

This study aimed to investigate the impact of different pre-heating temperatures (ranging from 40 °C to 80 °C) on the interactions between soy protein isolate (SPI) and catechin to effectively control catechin encapsulation efficiency and optimize the emulsifying properties of soy protein isolate. Results showed that optimal heat treatment at 70 °C improved catechin encapsulation efficiency up to 93.71 ± 0.14 %, along with the highest solubility, enhanced emulsification activity index and improved thermal stability of the protein. Multiple spectroscopic techniques revealed that increasing pretreatment temperature (from 40 °C to 70 °C) altered the secondary structures of SPI, resulting in a more stable unfolded structure for the composite system with a significant increase in α-helical structures and a decrease in random coil and β-sheet structures. Moreover, optimal heat treatment also leads to an augmentation of free sulfhydryl groups within complex as well as exposure of more internal chromophore amino acids on molecular surface. Size-exclusion high-performance liquid chromatography and SDS-PAGE analysis indicated that the band intensity of newly formed high-molecular-weight soluble macromolecules (>180 kDa) increased as the pre-heating temperature rose. Furthermore, fluorescence spectroscopy and molecular docking analysis suggest that hydrophobic and covalent interactions were involved in complex formation, which intensified with increasing temperature.

Improved encapsulation effect and structural properties of whey protein isolate by dielectric barrier discharge cold plasma

The whey protein isolate (WPI) was modified by dielectric barrier discharge cold plasma (DBD) in order to improve its encapsulation efficiency of rutin. In this work, the effect of DBD treatment on structure and physicochemical properties of WPI and the interaction between DBD-treated WPI and rutin were investigated. The results showed that the structural change of WPI leaded to the exposure of internal hydrophobic groups, increasing the interaction site with rutin. The encapsulation efficiency of DBD-treated WPI (30 kV, 30 s) on rutin was improved by 12.42 % compared with control group. The results of multispectral analysis showed that static quenching occurred in the process of interaction between DBD-treated and rutin, hydrogen bond and van der Waals force were the main forces between them. Therefore, DBD treatment can be used as a method to improve the encapsulation efficiency of WPI on hydrophobic active substances.

The effect of subzero temperatures on the properties and structure of soy protein isolate emulsions

Different freezing temperatures (-5, -20, -40 and -80 ℃) could change soy protein isolate (SPI) structure and emulsion properties. After freezing at -5 ℃ and -20 ℃, the structure of the SPI loosened, the fluorescence intensity was red shifted, and the proportion of Phe, Tyr and Trp exposed increased. With decreasing temperature, the surface hydrophobicity (H0 × 100), the number of sulfhydryl groups and the number of disulfide bonds all rose, then fell (-40 ℃), and rose again (-80 ℃). The β-sheet content in the protein secondary structure increased from 32.71% (control) to 50.66% (-40 ℃) and then decreased to 37.05% (-80 ℃), while the β-turn and random coil contents showed the opposite pattern, which also confirmed aggregation. The emulsification performance of SPI after freezing treatment was decreased. The results of this study provide theoretical support for future production of frozen foods with added SPI.

Enhancing silkworm protein yield, extraction efficiency, structure, functionality, and antioxidant activity using ultrasound-, microwave-, and freeze-thaw-assisted methods

BACKGROUND

Silkworm protein applications are limited in the food industry because of their low emulsifying and foaming properties. This study investigated the effect of ultrasound-assisted extraction (UAE) for 15 and 30 min, microwave-assisted extraction (MAE) for 1 and 2 min, and freeze-thaw-assisted extraction (FTAE) for one and three cycles on the yield, extraction efficiency, functional properties, and antioxidant activities of proteins from silkworm pupae. Relationships of protein structure and functionality were also examined.

RESULTS

UAE for 15 and 30 min and MAE for 1 and 2 min significantly increased protein yield and extraction efficiency compared to the control. Both UAE and MAE processes, especially MAE for 2 min, greatly improved the emulsifying and foaming properties of extracted proteins. FTAE one and three cycles did not increase the protein yield and extraction efficiency but showed enhanced functional properties, especially foaming. All samples showed changes in protein structure, such as increased exposed sulfhydryl (SH) contents, denaturation temperatures, and enthalpy. Only MAE samples had low-molecular-weight proteins based on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. UAE and FTAE samples had significantly higher antioxidant activities, while the MAE process showed the opposite.

CONCLUSION

UAE and MAE processes improved the yield and functionality of extracted silkworm proteins, while MAE negatively impacted protein antioxidant activities. © 2023 Society of Chemical Industry.

Effect of ultrasound treatment on thawing process of frozen tofu prepared with different salt coagulants

This study investigated the effects of ultrasound-assisted water thawing (UWT) at different power levels (0, 100, 150, 200, and 250 W) on the thawing rate and gel properties of frozen tofu made using three different salt coagulants (CaCl2, CaSO4, and MgCl2). Tofu produced with CaCl2 and CaSO4 elicited gel structures with dense and homogeneous networks, while that with MgCl2 had rough pores and irregular networks. UWT treatment significantly decreased thawing time by 30.9-53.5% compared to the control. Water holding capacity and scanning electron microscopy analyses demonstrated that UWT-100, UWT-150, and UWT-200 should be used to increase the amount of fixed water for CaCl2, CaSO4, and MgCl2. These findings suggest that appropriate ultrasonic treatment could improve the water retention capacity of the tofu network and make the gel network structure more compact. Additionally, protein structural analysis showed a decrease in the exposure of hydrophobic groups and reduced protein denaturation when tofu prepared with all the coagulants were thawed with UWT energies of 100-200 W ultrasonication. These findings offer theoretical support for improving the frozen tofu thawing process while ensuring optimal final product quality.

Effects of Freeze-Thaw Cycles on the Structures and Functional Properties of Clitocybe squamulosa Protein Isolates

Changes in the functional properties and structures of Clitocybe squamulosa protein isolate (CSPI) in the process of freeze-thaw (F-T) cycles were explored. Remarkable alterations and the reduced content of protein ordered structure were revealed through structural analysis of CSPI after F-T treatments. The surface hydrophobicity and free sulfhydryl content of CSPI first increased and then decreased. However, after the F-T treatments, the carbonyl content of CSPI continued to increase. Similarly, the water holding capacity (WHC), oil holding capacity (OHC), and solubility of CSPI all declined as the number of F-T cycles increased. The foaming properties and emulsifying properties of CSPI were significantly improved and reached maximum values after three F-T cycles. CSPI undergoing two F-T cycles showed the highest digestibility, maximum polypeptide content, and highest DPPH and ·OH-radical-scavenging activities. The ·OH-radical-scavenging activities and reducing power of the gastrointestinally digested CSPI had the highest value after one F-T cycle. Therefore, it has been demonstrated that F-T treatments could be a residue-free and cost-effective tool for improving mushroom protein functional properties.

Effect of Freezing on Soybean Protein Solution

To investigate the impact of frozen storage conditions on the physicochemical properties of soybean protein and explore the underlying mechanisms, this study focused on soybean isolate (SPI), ß-soybean companion globulin (7S), and soybean globulin (11S). The protein solutions were prepared at a concentration of 2% and subjected to freezing for 1 and 5 days. Subsequently, the protein content, physicochemical properties, secondary structure, sulfhydryl content, and chemical interaction forces were assessed and analyzed using UV spectrophotometry, Zeta potential measurements, SDS-PAGE, Fourier infrared spectroscopy, and endogenous fluorescence photoemission spectroscopy. The obtained results revealed that the solubility and total sulfhydryl content of SPI, 7S, and 11S exhibited a decreasing trend with prolonged freezing time. Among them, 11S demonstrated the largest decrease in solubility and total sulfhydryl content, followed by SPI, and 7S the least. During freezing, the aromatic amino acids of SPI, 7S, and 11S molecules were exposed, leading to increased hydrophobicity, protein aggregation, and particle size enlargement, and the structure of the protein changed from disordered structure to ordered structure. After freezing, the polarity of the microenvironment of SPI, 7S, and 11S increased, and their maximum fluorescence emission wavelengths were red-shifted. Notably, the largest red shift of SPI was from 332 nm to 335 nm. As freezing time increased, the contribution of hydrogen bonding increased, while the contribution of hydrophobic interactions decreased. This indicates that freezing affects the hydrophobic interactions, hydrogen bonding, and other chemical forces of the protein. The growth of ice crystals leads to the unfolding of protein molecular chains, exposure of internal hydrophobic groups, enhancement of hydrophobicity, and alters the secondary structure of the protein.

Improvement of functional characteristics of Hypophthalmichthys molitrix protein by modification with chitosan oligosaccharide

In the food processing field, it is very often that fish proteins are denatured affecting the nutritional value of the product which is vital to be solved. By using appropriate sugar donors for glycosylation with protein, improving the stability and emulsification properties of fish proteins can be achieved. This research looks into the impacts of enzymatic chitosan oligosaccharide (CO) at various concentration (0.15%, 0.30%, 0.45%, 0.60%, w/v) upon the molecular makeup and function of silver carp myofibrillar protein (MP) in an attempt to comprehend the impact of electrostatic binding among MP as well as CO on protein conformation. Analysis was done on the impact of various CO concentrations upon MP's secondary structure, conformational changes, and functional characteristics. Twelve sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) assays were implemented to monitor MP; Fourier transform infrared spectroscopy, endogenous fluorescence spectroscopy, and UV absorption spectra were carried out to investigate the influence of CO on MP; Particle size distribution, emulsifying activity index (EAI), solubility, turbidity, sulfhydryl content, carbonyl content, foaming capacity, surface hydrophobicity, emulsifying stability index (ESI), and foam persistence were all investigated. In addition, we used dynamic light scattering, scanning electron microscope, and atomic force microscope to analyze myosin (MO) and 0.60% CO-MO complex. The results demonstrated that CO and MP form complexes through hydrogen bonding and electrostatic interactions. CO modification not only delayed the oxidation of MP but also promoted MP to show better solubility, foaming, and foaming stability. In addition, CO modified myosin particle size decreased, reducing myosin's roughness and making myosin's structure more compact. To sum up, molecular interaction could change functional characteristics, and products with special properties could be developed after modification with chitosan oligosaccharide.

The complexes of soybean protein isolate and procyanidin B2 have synergistic hypolipidemic activity at the cellular level by activating the AMPKα pathway

The alkali method was used to prepare soybean protein isolate (SPI) and procyanidin B2 (PCB2) complexes, and the interaction between SPI and PCB2 was studied using multi-spectroscopic methods. The human hepatoma (HepG2) cell hyperlipidemia model was used to explore whether SPI-PCB2 has the potential for synergistic hypolipidemia. According to the findings, PCB2 was primarily linked to SPI via C-S and C-N bonds, and the addition of PCB2 reduced the α-helix structure content of SPI by 4.1%. At the cellular level, the optimal SPI-PCB2 ratio for lowering blood lipids was 1:1. Compared with the model group, the TG content and TC content in the 1:1 group were reduced by 28.7% and 26.3%, respectively. Western blot analysis revealed that SPI-PCB2 = 1:1 exerted synergistic hypolipidemic activity mainly by activating adenosine monophosphate-activated protein kinase α (AMPKα) phosphorylation, inhibiting 3-hydroxy-3-methylglutaryl CoA reductase (HMGCR) and fatty acid synthetase (FAS) protein expression, and upregulating carnitine palmitoyl transferase 1A (CPT1A) protein activity.

Are quinoa proteins a promising alternative to be applied in plant-based emulsion gel formulation?

Emulsion gels are structured emulsion systems that behave as soft solid-like materials. Emulsion gels are commonly used in food-product design both as fat replacers and as delivery carriers of bioactive compounds. Different plant-derived proteins like soy, chia, and oat have been used in emulsion gel formulation to substitute fat in meat products and to deliver some vegetable dyes or extracts. Quinoa protein isolates have been scarcely applied in emulsion gel formulation although they seem to be a promising alternative as emulsion stabilizers. Quinoa protein isolates have a high protein content with a well-balanced amino acid profile and show good emulsifying and gelling capabilities. Unlike quinoa starch, quinoa protein isolates do not require any chemical modification before being used. The present article reviews the state of the art in food emulsion gels stabilized with vegetable proteins and highlights the potential uses of quinoa proteins in emulsion gel formulation.

Physicochemical, structural and adhesion properties of walnut protein isolate-xanthan gum composite adhesives using walnut protein modified by ethanol

Low-sugar and high-protein adhesives have broad market application prospects, while natural plant proteins have confronted technical bottlenecks due to their poor adhesion. In this study, the effects of ethanol with different concentrations (0-80%) on the adhesion properties of walnut protein isolate-xanthan gum (WNPI-XG) composite adhesives were investigated. Results showed the bonding strength of WNPI-XG treated with 40% ethanol reached 12.55 MPa, the denaturation temperature and the surface hydrophobicity increased to 87.91 and 185.07 respectively, displaying the best rheological and texture properties. It also indicated appropriate concentration of ethanol (40%) didn't change the molecular weight of WNPI-XG, but greatly strengthened the fluorescence intensity, leading changes in contents of reactive sulfhydryl groups, electrostatic forces, hydrophobic interactions, hydrogen bonds and disulfide bonds. Furthermore, the treatment also facilitated a conformation conversion of the secondary structures from β-sheet to α-helix, promoting the full unfolding of protein molecules. The microstructure analysis showed after 40% ethanol treatment, the WNPI structure was uniform, the surface of WNPI-XG adhesive was flat and smooth, combined more closely with water molecules. By analyzing the influence of ethanol treatment on adhesion of WNPI-XG, the research laid a theoretical foundation for protein modification, providing good technical references for its development and utilization.

Modeling Tumor: Lymphatic Interactions in Lymphatic Metastasis of Triple Negative Breast Cancer

Simple Summary

Lymphatic metastasis is a critical prognostic factor of breast cancer aggressiveness and patient survival. Since existing therapeutic approaches have shown limited efficacy, new strategies to identify effective therapeutic targets for reducing breast cancer lymphatic metastasis are needed. We have used novel culture chambers, designed and fabricated by our group, to develop 3D models in which we can study spat ial interactions between breast cancer cells and lymphatic cells as they occur in real-time. This approach provides information on the complex cell–cell interactions involved in lymphatic metastasis of breast cancers. Factors in the secretome of the lymphatic cells promote invasive outgrowths from 3D cultures of breast cancer cells, suggesting that targeting interactions between breast cancer cells and lymphatic cells could be a potential therapeutic approach for the prevention of lymphatic metastasis.

Abstract

Breast cancer frequently metastasizes to lymphatics and the presence of breast cancer cells in regional lymph nodes is an important prognostic factor. Delineating the mechanisms by which breast cancer cells disseminate and spatiotemporal aspects of interactions between breast cancer cells and lymphatics is needed to design new therapies to prevent lymphatic metastases. As triple-negative breast cancer (TNBC) has a high incidence of lymphatic metastasis, we used a three-dimensional (3D) coculture model of human TNBC cells and human microvascular lymphatic endothelial cells (LECs) to analyze TNBC:LEC interactions. Non-invasive analyses such as live-cell imaging in real-time and collection of conditioned media for secretomic analysis were facilitated by our novel microfluidic chambers. The volumes of 3D structures formed in TNBC:LEC cocultures are greater than that of 3D structures formed by either LEC or TNBC monocultures. Over 4 days of culture there is an increase in multicellular invasive outgrowths from TNBC spheroids and an association of TNBC spheroids with LEC networks. The increase in invasive phenotype also occurred when TNBC spheroids were cultured in LEC-conditioned media and in wells linked to ones containing LEC networks. Our results suggest that modeling spatiotemporal interactions between TNBC and LECs may reveal paracrine signaling that could be targeted to reduce lymphatic metastasis.

The impact of quick-freezing methods on the quality, moisture distribution and microstructure of prepared ground pork during storage duration

The aim of present study was to investigate the influences of ultrasound-assisted immersion freezing (UIF), immersion freezing (IF) and air freezing (AF) on the quality, moisture distribution and microstructure properties of the prepared ground pork (PGP) during storage duration (0, 15, 30, 45, 60, 75 and 90 days). UIF treatment significantly reduced the freezing time by 60.32% and 39.02%, respectively, compared to IF and AF (P < 0.05). The experimental results of quality evaluation revealed that the L* and b* values, juice loss, cooking loss, TBARS values and carbonyl contents were decreased in the UIF treated samples, while the a* value, peak temperatures (Tm), enthalpy (ΔH) and sulfhydryl contents were significantly higher than those of IF and AF treated samples (P < 0.05). In addition, low-field nuclear magnetic resonance (LF-NMR) and differential scanning calorimetry (DSC) analysis demonstrated that UIF inhibited the mobility of immobilized water and reduced the loss of immobilized and free water, and then a high water holding capacity (WHC) was achieved. Compared to the IF and AF treatments, the UIF treated PGP samples possessed better microstructure. Therefore, UIF could induce the formation of ice crystals with smaller size and more even distribution during freezing process, which contributed to less damage to the muscle tissue and more satisfied product quality.

Ultrasonic Freezing Reduces Protein Oxidation and Myofibrillar Gel Quality Loss of Common Carp (Cyprinus carpio) during Long-Time Frozen Storage

Ultrasonic freezing (UF) is an effective method to increase the freezing speed and improve the quality of frozen food. The effect of UF on myofibrillar protein oxidation and gel properties of common carp (Cyprinus carpio) during frozen storage were investigated with air freezing (AF) and immersion freezing (IF) as controls. The results showed that the carbonyl and dityrosine content of UF samples were lower and the free amine content was higher than those of AF and IF samples during frozen storage indicating that UF inhibited protein oxidation caused by frozen storage. The particle size of UF myofibrillar protein was the smallest among all the groups indicating that UF inhibited the protein aggregation. The UF sample had higher G', G" value, gel strength and gel water holding capacity than AF and IF groups showing that UF reduced the loss of protein gel properties. The gel microstructure showed that UF protein gel was characterized by smaller and finer pores than other samples, which further proves that UF inhibited loss of gel properties during frozen storage. The UF sample had shorter T2 transition time than other samples demonstrating that UF decreased the mobility of water. In general, UF is an effective method to reduce protein oxidation and gel properties loss caused by frozen storage.

Effects of different thawing methods on conformation and oxidation of myofibrillar protein from largemouth bass (Micropterus salmoides)

This study examined the effects on conformation and oxidation of myofibrillar protein in largemouth bass by different thawing methods. The conventional thawing, microwave thawing, microwave (MVT) or ultrasound combined with vacuum thawing, microwave or far-infrared thawing (FMT) combined with magnetic nanoparticles were used in this experiment. The physicochemical changes were analyzed by differential scanning calorimetry and dynamic rheology. The protein structure changes were measured by Raman, intrinsic fluorescence, and second-derivative ultraviolet spectrometry. The degree of protein aggregation was evaluated by surface hydrophobicity, particle size, and zeta-potential measurements. Total sulfhydryl content, protein carbonyl content, Ca²⁺ -ATPase activity, and SDS-PAGE were used to analyze the degree of protein oxidation. Results showed that MVT and FMT samples had better thermal stability, more stable protein conformation, and a lower degree of protein oxidation. Thus, these two methods would be beneficial to sustain the quality of thawed fillets. PRACTICAL APPLICATIONS: In the market circulation, largemouth bass (Micropterus salmoides) need to be frozen. The thawing methods can directly affect the quality of frozen fish, thus causing the changes in the conformation of the myofibrillar protein in fish, and also affecting the degree of protein oxidation. The results showed that the microwave combined with vacuum and the magnetic nanoparticles combined with far-infrared thawing had less effect on myofibrillar protein of fish and were a better thawing method.

Sonochemical action and reaction of edible insect protein: Influence on enzymolysis reaction-kinetics, free-Gibbs, structure, and antioxidant capacity

We investigated the impact of sonochemical action and the reaction of Hermetia illucens larvae meal protein (HILMP) as regards enzymolysis under varied enzyme concentration and temperature to explain the mechanism and effect of sonication on molecular conformation, limits of kinetics, free-Gibbs energy, and antioxidative capacity. Control treatment was used for comparison. The results showed sonochemical treatment enhanced HILMP-enzymolysis efficiency at various enzyme volume, and temperature. Enzymolysis-kinetics revealed sonochemical treatment increased the rate constant (p < .05) by 17.21%, 25.06%, 26.91%, and 41.38% at 323, 313, 303, and 293 K, respectively. On free-Gibbs, sonochemical treatment reduced the reactants-reactivity energy, enthalpy, and entropy by 30.53%, 35.05%, and 10.71%, respectively (p < .05). Changes in spectra of UV and fluorescence, and micrographic imaging indicated alterations of HILMP by sonochemical treatment. Antioxidative activity of sonochemically-treated HILMP increased, compared to control. Thus, sonochemical treatment may be beneficial in the production of edible insect proteins with smaller molecular weights for different food and/or pharmaceutical applications. PRACTICAL APPLICATIONS: Sonochemical pretreatment of HILMP positively impacted it enzymolysis rate-reaction, stability of reaction products, structure, and bioactivity. Thus, the technique may be beneficial to industry in the processing/development of new (bioactive/pharmaceutical) products involving enzymolysis of edible insects (e.g., Hermetia illucens) protein; particularly at such a time where edible insects are projected to be a source of protein for human nutrition and livestock in the next few years.

Effects of ultrasonics combined with far infrared or microwave thawing on protein denaturation and moisture migration of Sciaenops ocellatus (red drum)

The influence of ultrasonics combined with microwave thawing (UMT) and ultrasonics combined with far-infrared thawing (UIT) on the water migration and protein denaturation of red drum were studied. Five treatments were used: ultrasonics thawing (UT), microwave thawing (MT), far-infrared thawing (IT), UIT and UMT were used for thawing red drum filets. Moisture migration and protein aggregation were studied using nuclear magnetic resonance (NMR) and particle size, respectively. Raman spectra and fluorescence spectra were used to study the secondary and tertiary structure of protein. SEM was done to observe the fiber microstructure. The results showed that UMT and UIT can maintained protein stability more than other thawing methods and retained the fiber structure of the muscle. Besides, immobilized water in fiber bundles network also had no significant changes compared with fresh samples. Thus, ultrasonics combined with far infrared or microwave thawing were used to decrease protein denaturation and water migration during the thawing of Red drum fillets.

Effects of ultrasound-assisted freezing at different power levels on the structure and thermal stability of common carp (Cyprinus carpio) proteins

This study investigated the effect of ultrasound-assisted immersion freezing (UIF) at different ultrasonic power levels on the myofibrillar protein primary, secondary and tertiary structures of common carp (Cyprinus carpio). Furthermore, protein thermal stability, electrophoresis pattern, and microstructure of the muscle tissue were also studied. Compared with a control, an ultrasonic power of less than 175 W had no significant negative effect on protein primary structure (P > 0.05), including total sulfhydryl, reactive sulfhydryl, carbonyl groups, free amino groups, dityrosine content, and surface hydrophobicity. UIF at 175 W (UIF-175) minimized the changes in protein secondary and tertiary structures. There were no obvious changes in the SDS-PAGE patterns of the control and frozen sample proteins. Microstructure analysis showed that an appropriate ultrasonic power (UIF-175) promoted the formation of smaller and more uniform ice crystals, reduced the damage of muscle tissue by ice crystals, and maintained the sarcomere integrity. In addition, UIF-175 samples had higher protein thermal stability. Overall, ultrasound treatment at a proper power (UIF-175) effectively minimized the changes in protein structure and protected the protein thermal stability during freezing process.

Effect of different time of ultrasound treatment on physicochemical, thermal, and antioxidant properties of chicken plasma protein

The aim of present study was to investigate the effect of different times (5 min (UCPP-5), 10 min (UCPP-10), 20 min (UCPP-20), and 30 min (UCPP-30)) of ultrasound treatment on physicochemical, thermal, and antioxidant properties of chicken plasma protein (CPP). UCPP-20 had the highest fluorescence intensity and the lowest particle size. However, no major changes in the subunit compositions and the secondary structure of UCPPs were presented in SDS-PAGE and circular dichroism. The surface hydrophobicity and sulfhydryl content of UCPPs increased significantly (P < 0.05) as compared to those of CPP. With the increasing time of ultrasound treatment, there were more and deeper holes on the protein surfaces. Furthermore, protein modification by ultrasound could improve the thermal properties of UCPPs. Additionally, UCPPs showed a significant increase in antioxidant properties over CPP, especially UCPP-20. These observations indicated that ultrasound treatment was necessary for modification of CPP to meet the requirements for food processing.