Changes in the myosin secondary structure and shrimp surimi gel strength induced by dense phase carbon dioxide

Thermal aggregation behavior of silver carp myofibrillar protein at low salt content: Effect of oat β-glucan combined with ultrasound-assisted heating

The effects of oat β-glucan (OG) combined with ultrasound-assisted treatment on thermal aggregation behavior of silver carp myofibrillar protein (MP) under low salt concentration were investigated. The particle size and turbidity of MP were increased to higher levels by OG participation or ultrasound treatment during the two-stage heating. Both OG and ultrasonic treatment promoted the unfolding of MP structure, evidenced by the gradual decrease of α-helix content and fluorescence intensity, as well as the increase of β-sheet content, surface hydrophobicity and sulfhydryl content. Compared to solely OG or ultrasonic treatment, the combination of OG and ultrasound further promoted the unfolding of MP and more sulfhydryl groups were exposed in the pre-heating stage, which was conducive to strengthen the chemical forces between MP molecules. Additionally, AFM analysis revealed that the apparent morphology of the OG combined with ultrasonic treated group exhibited a smoother surface and a more uniform distribution of aggregates.

Influence mechanisms of linoleic acid and oleic acid on the gel properties of egg yolk protein

BACKGROUND

Gel property is among the crucial functional properties of egg yolk (EY), which determines the texture and flavor of EY products. In the present study, the effects of two unsaturated fatty acids [monounsaturated fatty acid oleic acid (OA) and diunsaturated fatty acid linoleic acid (LA)] on the gel properties of EY protein were investigated.

RESULTS

Compared with the blank group, the addition of LA and OA (10-50 g kg-1) improved the gel hardness (from 270.54 g to 385.85 g and 414.38 g, respectively) and viscosity coefficient (from 0.015 Pa.sn to 11.892 Pa.sn and 1.812 Pa.sn, respectively). The surface hydrophobicity of EY protein increased to a maximum value of 40 g kg-1 with the addition of both fatty acids (39.06 μg and 41.58 μg, respectively). However, excess unsaturated fatty acids (≥ 50 g kg-1) disrupted the completeness of the gel matrix and weakened the structural properties of the EY gel.

CONCLUSION

Both fatty acids improved the gel properties of EY protein. At the same addition level, OA was superior to LA in improving gel properties. The present study provides a theoretical underpinning for the sensible application of unsaturated fatty acids in improving EY gel properties. © 2024 Society of Chemical Industry.

Effect of κ-carrageenan on the quality of crayfish surimi gels

The demand for crayfish surimi products has grown recently due to its high protein content. This study examined the effects of varying κ-carrageenan (CAR) and crayfish surimi (CSM) concentrations on the gelling properties of CAR-CSM composite gel and its intrinsic formation process. Our findings demonstrated that with the increasing concentration of carrageenan, the quality of CAR-CSM exhibited rising trend followed by subsequently fall. Based on the textural qualities, the highest quality CAR-CSM was achieved at 0.3% carrageenan addition. With the exception of chewiness, and the cooking loss of the gel system was 1.62%, whiteness was 82.35%, and the percentage of β-sheets increased to 57.18%. Further increase in CAR (0.4-0.5%) addition resulted in internal build-up of LCAR-CSM, conversion of intermolecular forces into disulfide bonds and gel breakage. This study exudes timely recommendations for extending the CAR application for the continuous development of crayfish surimi and its derivatives and its overall economic worth.

Effect of L-cysteine on the physicochemical properties of heat-induced sheep plasma protein gels

The effects of different l-Cysteine additions (0-2 %) on the gel properties, microstructure and physicochemical stability of sheep plasma protein gels were studied. The introduction of l-Cys significantly improved the water retention capacity and whiteness of the plasma protein gel (p < 0.05). The addition of 0.2 %-0.4 % l-Cys increased gel strength, but l-Cys had no significant effect on gel elasticity (p < 0.05). Scanning electron microscopy confirmed that the addition of l-Cys also promoted the formation of a porous three-dimensional network structure in the gel. Raman spectroscopy and SDS-PAGE revealed that the addition of l-Cys generally reduced α-helix structures in protein gels and promoted the formation of β-folds. Addition of 0.2 % l-Cys treatment leading to the greatest increase in disulfide bonds, and its surface hydrophobicity and endogenous fluorescence intensity were the largest. At this time, the comprehensive performance of sheep plasma protein gel is the best performance.

Effect of psyllium husk powder on the gelation behavior, microstructure, and intermolecular interactions in myofibrillar protein gels from Andrias davidianus

The interaction between proteins and soluble dietary fibers plays a vital role in the development of animal-derived foods. Herein, the effects of different contents (0-3.0%) of round-bracted psyllium husk powder (PHP) on the gelation behavior, microstructure, and intermolecular interactions of Andrias davidianus myofibrillar protein (MP) were investigated. Rheological and chemical forces suggested that PHP (1.5%-2.0%) enhanced the functional properties of MP at low ionic strength, thereby increasing the viscoelasticity of mixed gels. SDS-PAGE revealed that PHP reinforced the cross-linking and aggregation of protein molecules. Circular dichroism spectroscopy, low-field nuclear magnetic resonance, and scanning electron microscopy demonstrated that PHP induced the transformation of α-helix (decreased by 14.85%) to an ordered β-sheet structure (increased by 81.58%), which was more favorable for the formation of dense network structure and improved (10.53%) the water retention of MP gels. This study provided new insights for PHP to effectively meliorate the heat-induced gelling properties of MP.

Unraveling the potential of non-thermal ultrasonic contact drying for enhanced functional and structural attributes of pea protein isolates: A comparative study with spray and freeze-drying methods

The challenge of preserving the quality of thermal-sensitive polymeric materials specifically proteins during a thermal drying process has been a subject of ongoing concern. To address this issue, we investigated the use of ultrasound contact drying (USD) under non-thermal conditions to produce functionalized pea protein powders. The study extensively examined functional and physicochemical properties of pea protein isolate (PPI) in powder forms obtained through three drying methods: USD (30 °C), spray drying (SD), and freeze drying (FD). Additionally, physical attributes such as powder flowability and color, along with morphological properties, were thoroughly studied. The results indicated that the innovative USD method produced powders of comparable quality to FD and significantly outperformed SD. Notably, the USD-PPI exhibited higher solubility across all pH levels compared to both FD-PPI and SD-PPI. Moreover, the USD-PPI samples demonstrated improved emulsifying and foaming properties, a higher percentage of random coil form (56.2 %), increased gel strength, and the highest bulk and tapped densities. Furthermore, the USD-PPI displayed a unique surface morphology with visible porosity and lumpiness. Overall, this study confirms the effectiveness of non-thermal ultrasound contact drying technology in producing superior functionalized plant protein powders, showing its potential in the fields of chemistry and sustainable materials processing.

Insight into the allergenicity and structure changes of parvalbumin from Trachinotus ovatus induced by dense-phase carbon dioxide

Parvalbumin (PV) is a major allergen in fish, and traditional treatments cannot reduce its sensitization. The effects of dense-phase carbon dioxide (DPCD) treatment on the sensitization and spatial structure of PV in Trachinotus ovatus were evaluated in this study. Western blotting and indirect ELISA were used to determine the allergenicity changes and spatial conformations of PV treated by DPCD. Tris-tricine-SDS-PAGE, circular dichroism, surface hydrophobicity, endogenous fluorescence, UV spectrophotometry, free amino group, total sulfhydryl group and SEM analyses were applied to characterize PV structure. The results showed that DPCD treatment (15 MPa, 30 min, 50 °C) could reduce PV-induced allergic reactions by 39-41 %, which destroyed the normal conformational epitopes and reduced the risk of PV-induced allergy. The secondary structure changed from ordered to disordered with a decreased content of α-helical groups, while the internal hydrophobic groups were exposed. The total sulfhydryl group content decreased significantly (P < 0.05). The surface hydrophobicity and ultraviolet absorption spectrum were enhanced, and the endogenous fluorescence peak shifted to a long wavelength. Meanwhile, the content of free amino groups increased significantly (P < 0.05). This study could provide a theoretical basis and a promising technical approach for reduction of PV allergenicities.

Effects of nitrogen fertilizer on the physicochemical, structural, functional, thermal, and rheological properties of mung bean (Vigna radiata) protein

Nitrogen fertilizer can affect the seed quality of mung bean. However, the effects of nitrogen fertilizer on the properties of mung bean protein (MBP) remain unclear. We investigated the effects of four nitrogen fertilization levels on the physicochemical, structural, functional, thermal, and rheological properties of MBP. The results showed that the amino acid and protein contents of mung bean flour were maximized under 90 kg ha-1 of applied nitrogen treatment. Nitrogen fertilization can alter the secondary and tertiary structure of MBP. The main manifestations are an increase in the proportion of β-sheet, the exposure of more chromophores and hydrophobic groups, and the formation of loose porous aggregates. These changes improved the solubility, oil absorption capacity, emulsion activity, and foaming stability of MBP. Meanwhile, Thermodynamic and rheological analyses showed that the thermal stability, apparent viscosity, and gel elasticity of MBP were all increased under nitrogen fertilizer treatment. Correlation analysis showed that protein properties are closely related to changes in structure. In conclusion, nitrogen fertilization can improve the protein properties of MBP by modulating the structure of protein molecules. This study provides a theoretical basis for the optimization of mung bean cultivation and the further development of high-quality mung bean protein foods.

A comprehensive review on hempseed protein: Production, functional and nutritional properties, novel modification methods, applications, and limitations

With the global population on the rise, challenges in meeting protein demands are amplified by recent crises, prompting a swift shift to alternative protein sources due to disruptions in the supply chain. Plant-based proteins are gaining momentum due to economic, cultural, and environmental considerations, aligning with the preference for sustainable diets and resulting in more affordable plant-based products. The distinction between drug and industrial hemp fuels demand for its nutritional value, digestibility, low allergenicity, and bioactive properties. Industrial hempseed, featuring minimal Δ9-Tetrahydrocannabinol (THC) content (<0.2 %), emerges as a promising crop, offering high-quality protein and oil. The de-oiled hempseed cake stands as an eco-friendly and promising protein source enriched with phenolic compounds and fiber. Ongoing research seeks to enhance techno-functional properties of hempseed protein, surmounting initial limitations for integration into various foods. A range of techniques, both conventional and innovative, optimize protein characteristics, while modifying plant-based protein structures augments their application potential. Modification approaches like ultrasound, high-pressure homogenization, conjugation, complexation, fibrillization, and enzymatic methods enhance hempseed protein functionality. The review critically evaluates the techno-functional attributes of hempseed protein and explores strategies for customization through structural modifications. Lastly, the review assesses its composition, potential as a plant-based source, addresses challenges, and discusses strategies for enhanced functionality.

Quantitative analysis of the correlation between gel strength and microstructure of shrimp surimi gel induced by dense phase carbon dioxide

The impact of treatment pressure, temperature and time of DPCD on the Pacific White Shrimp (Litopenaeus vannamei) surimi gel properties was studied and compared with the conventional heat treatment. The gel strength, crosslinking degree, and microstructure of shrimp surimi gels were investigated. Quantitative microstructural characteristics were investigated to elucidate the changes in microstructure during the formation of gel induced by DPCD. With increased DPCD treatment setting conditions, the gel strength and crosslinking degree of shrimp surimi gel significantly improved (P < 0.05) with similar variation trends. Quantitative microstructural analysis revealed that the fractal dimension (Df) and the pore equivalent diameter of gel microstructure increased with the increase of DPCD treatment conditions. The lacunarity decreased and then increased, whereas pore number increased and decreased. According to the microstructural characteristics results, the surimi gel with 51.48 % degree of crosslinking induced at 25 MPa, 50˚C, and 60 min showed the most complex and homogeneous microstructure with the highest (Df), smaller lacunarity, an average pore equivalent diameter, and a larger pore number. The correlation analysis demonstrated that the crosslinking degree was strongly positively correlated with the gel strength. The Df, pore equivalent diameter and number of pores significantly positively correlated with the crosslinking degree, whereas the lacunarity strongly negatively correlated with the crosslinking degree. The present study showed that the DPCD treatment with a crosslinking degree of 51.48 % is the most optimum condition for better gel formation. The study could provide a theoretical basis for processing shrimp surimi with improved gel properties.

Intermolecular forces regulate in-vitro digestion of whey protein emulsion gels: Towards controlled lipid release

HYPOTHESIS

The utilization of emulsion-filled protein hydrogels for controlled lipid release in the gastrointestinal tract (GIT) displays great potential in drug delivery and obesity treatment. However, how intermolecular interactions among protein molecules influence lipid digestion of the gels is still understudied.

EXPERIMENTS

Differently structured whey protein emulsion gels were fabricated by heating emulsions with blocking of disulfide bonds (the "noncovalent" gel), noncovalent interactions (the "disulfide" gel), or neither of these (the "control" gel). The intermolecular interactions-gel structure-lipid digestion relationship was investigated by characterizing structural/mechanical properties of the gels and monitoring their dynamic breakdown in a simulated GIT.

FINDINGS

Although the disulfide-crosslinked protein network formed thick interfacial layers around oil droplets and resisted intestinal proteolysis, the "disulfide" gel had the fastest lipolysis rate, indicating that it could not inhibit the access of lipases to oil droplets. In contrast, the "noncovalent" gel was more susceptible to in-vitro digestion than the "control" gel because of lower gel strength, resulting in a faster lipolysis rate. This demonstrated that intermolecular disulfide bonds and noncovalent interactions played distinctive roles in the digestion of the gels; they represented the structural backbone and the infill in the gel structure, respectively.

Collagens for surimi gel fortification: Type-dependent effects and the difference between type I and type II

Surimi products have unsatisfactory gel properties. Hence, this study evaluates the effect of collagen-adding on surimi gel properties and provides the first observation results regarding collagen type influence. With higher water solubility and more charged amino acids than type II, collagen type I intertwines with surimi myofibrillar proteins better to induce higher exposure of protein functional domains, more sufficient conformational changes of myosin and greater formation of chemical forces among proteins. These enhancements accelerate the gelation rate, leading to a well-stabilized surimi gel. The collagen I-containing surimi gels show more compact structures with uniformly distributed smaller pores than those containing collagen II, thereby providing the final products with higher water holding capacity and better textural profiles. As such, the surimi gel fortification performance of collagen I and the well-elucidated collagen-myofibrillar protein interaction mechanism will guide the further exploitation of collagen as an effective additive in the food industry.

Correlation between Water Characteristics and Gel Strength in the Gel Formation of Golden Pompano Surimi Induced by Dense Phase Carbon Dioxide

The relationship between the gel quality of golden pompano surimi treated with dense phase carbon dioxide (DPCD) and changes in water characteristics was evaluated. Low-field nuclear magnetic resonance (LF-NMR) and nuclear magnetic resonance imaging were used to monitor changes in the water status of surimi gel under different treatment conditions. Whiteness, water-holding capacity and gel strength were used as the quality indicators of the surimi gel. The results showed that DPCD treatment could significantly increase the whiteness of surimi and the strength of the gel, while the water-holding capacity decreased significantly. LF-NMR analysis showed that, as the DPCD treatment intensity increased, the relaxation component T₂₂ shifted to the right, T₂₃ shifted to the left, the proportion of A₂₂ decreased significantly (p < 0.05) and the proportion of A₂₃ increased significantly (p < 0.05). A correlation analysis of water characteristics and gel strength showed that the water-holding capacity of surimi induced by DPCD was strongly positively correlated with gel strength, while A₂₂ and T₂₃ were strongly negatively correlated with gel strength. This study provides helpful insights into the quality control of DPCD in surimi processing and also provides an approach for the quality evaluation and detection of surimi products.

Enhanced Gel Properties of Duck Myofibrillar Protein by Plasma-Activated Water: Through Mild Structure Modifications

This study assessed the gel properties and conformational changes of duck myofibrillar protein (DMP) affected by plasma-activated water (PAW) generated at various discharge times (0 s, 10 s, 20 s, 30 s, and 40 s). With the treatment of PAW-20 s, the gel strength and water-holding capacity (WHC) of DMP gels were significantly increased when compared to the control group. Throughout the heating process, dynamic rheology revealed that the PAW-treated DMP had a higher storage modulus than the control. The hydrophobic interactions between protein molecules were significantly improved by PAW, resulting in a more ordered and homogeneous gel microstructure. The increased sulfhydryl and carbonyl content in DMP indicated a higher degree of protein oxidation with PAW treatment. Additionally, the circular dichroism spectroscopy demonstrated that PAW induced α-helix and β-turn transformed to β-sheet in DMP. Surface hydrophobicity, fluorescence spectroscopy, and UV absorption spectroscopy suggested that PAW altered DMP's tertiary structure, although the electrophoretic pattern indicated that the primary structure of DMP was mostly unaffected. These results suggest that PAW can improve the gel properties of DMP through mild alteration in its conformation.

Gelation Process Optimization of Shrimp Surimi Induced by Dense Phase Carbon Dioxide and Quality Evaluation of Gel

Dense phase carbon dioxide (DPCD) is a new non-thermal method to induce surimi gel. However, the gel quality is affected by many factors, such as DPCD treatment time, temperature, and pressure, which makes it complicated to determine its operating parameters. Box-Behnken and backward linear regression were used to optimize the conditions (temperature, pressure, and treatment time) of DPCD-induced shrimp surimi gel formation, and a model between shrimp surimi gel strength and treatment conditions was developed and validated in the present study. Meanwhile, the heat-induced method was used as a control to analyze the effect of DPCD on the quality of shrimp surimi gel in the present study. The results showed that DPCD treatment affected the strength of shrimp surimi gel significantly, and the pressure of DPCD had the greatest influence on the gel strength of shrimp surimi, followed by time and temperature. When the processing pressure was 30 MPa, the temperature was 55 °C, and the treatment time was 60 min, the gel strength of the shrimp surimi was as high as 197.35 N·mm, which was not significantly different from the simulated value of 198.28 N mm (p > 0.05). The results of the gel quality properties showed that, compared with the heat-induced method, DPCD reduced the nutrient and quality loss of the shrimp surimi gel, and increased the gel strength and gel water-holding capacity. The results of low-field nuclear magnet resonance showed that DPCD increased the binding capacity of shrimp surimi to bound water and immobilized water, and reduced their losses. Gel microstructure further demonstrated that DPCD could improve shrimp surimi gelation properties, characterized by a finer and uniformly dense gel network structure. In summary, DPCD is a potential method for inducing shrimp surimi to form a suitable gel. The prediction model established in this study between DPCD treatment temperature, pressure, time, and gel strength can provide a reference for the production of shrimp surimi by DPCD.

Effects of microbial transglutaminase on textural, water distribution, and microstructure of frozen-stored longtail southern cod (Patagonotothen ramsayi) fish mince gel

Frozen-stored fish mince tend to have poor gelling ability due to significant myosin denaturation caused by freezing. In this study, microbial transglutaminase (MTGase) was used to improve the quality of fish mince gel products made from frozen-stored longtail southern cod (LSC). The gel strength of the gel product increased with the addition of MTGase and reached a plateau value of ~19 N mm beyond 300 U/kg of MTGase, at the same condition, T₂₂ was reduced from 57.22 to 49.77 ms, T₂₃ was reduced from 1,273.88 to 1,072.27 ms. As the MTGase addition increased from 0 to 400 U/kg, the hardness of the fish surimi gel increased from 14.52 to 21.36 N, and the microstructure changed from loose to dense, respectively. This study showed that MTGase could promote gelation to improve the quality of frozen-stored LSC fish mince gel, especially at 300 U/kg, which potentially can be utilized to produce good surimi gel products out of frozen-stored fish.

Modifying textural and functional characteristics of fish (Nemipterus japonicus) mince using high pressure technology

Effect of high pressure in inducing textural and functional modification has been investigated in pink perch (Nemipterus japonicus) mince. Fish mince undergone pressurization at 200, 400 and 600 MPa for a holding period of 10 min and was compared against cooked mince (90 °C; 40 min). The treated mince at 400 and 600 MPa lost its natural viscosity and behaved like cooked mince through denaturation and formation of protein aggregates. Textural characterisation showed the retention of tenderness in 200 MPa treated samples, but become harder on application of higher pressures. Unlike heat gels, pressure induced gels were more smooth, white and elastic in nature. A decreased in reactive SH groups was observed in 400 and 600 MPa treated samples due to the formation of disulfide bonds. Hydrophobic concentration was higher in cooked and 600 MPa treatments whereas Ca2+-ATPase activity decreased after pressurization. On application of different pressures microbial reduction of 2-3 log cycles was achieved in the mince samples. Hence pressure treatments at lower ranges cannot alter the texture and functionality of protein and the mince can undergo processing as required. Besides extending shelf life, the treatments above 400 MPa can make irreversible effect on texture quality and protein functionality which is similar to that of cooking.

Effects of heat treatment and pH on the physicochemical and emulsifying properties of coconut (Cocos nucifera L.) globulins

The present study aimed to assess the effects of heat treatment (70-90 °C) and pH (pH 3-11) on the physicochemical, structural, and emulsifying properties of coconut globulins (CG). The results revealed that the emulsifying property was improved with increasing temperature due to the denaturation degree of CG. CG had a better emulsifying property at pH 3 but showed the worst emulsifying property at pH 5 due to its lowest solubility, surface hydrophobicity, and absolute value of zeta potential. The best emulsifying stability was detected at pH 11 with 90 °C heating. SDS-PAGE indicated that the formation of aggregates cross-linked by covalent bonds was the main reason for the better emulsion stability at pH 3 and pH 11 with 90 °C heating. The secondary structure showed that CG had more α-helix and β-turn contents as well as fewer β-sheet contents at pH 3 and pH 11 with 90 °C heating.

Quark Cheese Processed by Dense-Phase Carbon Dioxide: Shelf-Life Evaluation and Physiochemical, Rheological, Microstructural and Volatile Properties Assessment

Dense-phase carbon dioxide (DPCD), a novel non-thermal processing technology, has attracted extensive attention due to its excellent performance in food sterilization and enzyme inactivation without quality deterioration. In this work, we aimed to extend the shelf life of quark cheese with DPCD and explore the effect of DPCD treatment as well as storage time on the quality of quark cheese. The sterilization parameters were optimized by means of orthogonal experiments, and the physiochemical, rheological, microstructural and volatile properties of cheese were investigated. The optimal DPCD treatment (20 MPa, 45 min, 55 °C) successfully extended the shelf life of quark cheese due to its inhibition effect on yeast and was able to slow down the proteolysis and alterations in pH and color of cheese. Cheese processed using DPCD after 14-day storage even displayed similar rheological properties to the control at day 0, from which bound water significantly migrated during storage. Moreover, DPCD contributed to the retention of the volatile profile of cheese during storage. This study demonstrated that DPCD is a promising pasteurization technology for quark cheese to improve its quality stability during storage.

Casein-hempseed protein complex via cross-link catalyzed by transglutaminase for improving structural, rheological, emulsifying and gelation properties

In present study, microbial transglutaminase (MTGase) was applied to strengthen the interaction between casein and hempseed protein (HPI) through crosslinking. The structural and functional characteristics of this heteropolymers were investigated. Both homologous and heterologous crosslinking were achieved by adding MTGase in casein-HPI system, and thus enhanced zeta potential, surface hydrophobicity, viscosity, emulsifying and gelation properties of the complex. However, HPI hindered the crosslinking due to unbalanced Lys/Gln ratios. Emulsifying and gelling properties were significantly correlated with the secondary structures. When MTGase activity was < 30 U/g or treatment time was < 2 h, the α-helix content decreased by 9% while the β-sheet content increased by 12%, respectively, with MTGase activity and treatment time increase. The structural alterations resulted in the better emulsifying activity, gel networks and water holding capacity of the complex. This work represents a novel interaction mode between casein and HPI via MTGase to elevate functional properties of complex.

Gel Properties of Blue Round Scad (Decapterus Maruadsi) Mince as Influenced by the Addition of Egg White Powder

The use of egg white powder (EWP) to enhance the physicochemical properties, molecular structure, and thermal stability of Decapterus maruadsi mince gels was investigated. The thermal stability was analyzed by adding spray-dried EWP (0%, 0.2%, 0.4%, 0.6%, 0.8%, 1%) to the mince, and mince gels were prepared to study the changes in their fracture constant, water distribution, microstructure and protein conformation of mince gels. In addition, the stress-strain curve of the EWP-mince gel was measured to obtain its compressive modulus (E). The formation of the mince gel was promoted by EWP, and the whiteness, fracture constant, water-holding capacity, and immobilized water were all enhanced. At 0.8% addition of EWP, the fracture constant increased from 176.715±2.463 N/m to 348.631±3.144 N/m (p<0.05), which was a nearly twofold improvement. Additionally, the water-holding capacity increased from 75.21% to 79.99%, and the percentage of immobilized water increased from 94.03% to 94.91%. The EWP-mince gel network structure was the most uniform and dense, and there were increases in hydrogen bonds, disulfide bonds, β-sheets, and β-turns in mince gels, as well as the storage modulus (G') and enthalpy (ΔH). In contrast to the control group, the relative content of α-helixes decreased from 53.34% to 37.09% and transformed into other secondary structures, and the bulk water and cooking loss also decreased to 2.41% and 8.51%, respectively. Consequently, EWP effectively improved the quality of mince products, and the effect was most apparent when 0.8% was added.

Ultrasonic pretreatment improves the gelation properties of low-salt Penaeus vannamei (Litopenaeus vannamei) surimi

The effects of different ultrasonic pretreatments (120-600 W, 20 min; 360 W, 10-30 min) on the gel properties of shrimp surimi were investigated. Gel properties and protein functional properties were analysed to clarify the mechanism of action of ultrasound. The gel strength, water holding capacity and surface hydrophobicity of shrimp surimi gel increased initially and then decreased with the increase in ultrasound power or time, but the change in total sulfhydryl content showed the opposite trend, which indicated that proper ultrasound pretreatment could improve the gel properties of shrimp surimi, expand the protein to a greater extent and expose more SH groups and hydrophobic groups. According to scanning electron microscopy observation, ultrasound made shrimp surimi gel form a denser gel network. Fourier transform infrared analysis indicated that the α-helix content in shrimp surimi gel decreased initially and then increased with the increase of in ultrasound power or time, whereas the change in β-sheet content showed the opposite trend. And the protein was the most stable in 360 W/20 min pretreatment. SDS-PAGE patterns showed that proper ultrasound inhibited the degradation of actin and troponin C. In addition, dynamic rheology illustrated that the G' values of the ultrasonic pretreatment group were higher than that of the control group, indicating that ultrasound could improve the elasticity and stability of shrimp surimi gel. The results suggested that the shrimp surimi gel pretreated by 360 W/20 min ultrasound showed the best gel properties. Furthermore, the correlation between the indexes affecting the properties of the gel was analyzed. This study provides a new technical means to improve the gel properties of shrimp surimi.

Effect of acetylated distarch adipate on the physicochemical characteristics and structure of shrimp (Penaeus vannamei) myofibrillar protein

To investigate the effect of acetylated distarch adipate (ADA) on the physicochemical properties and structure of shrimp myofibrillar protein (MP), the changes in chemical bonds, secondary structure and protein composition of shrimp MP and MP gel (MPG) were analyzed. Besides, the microstructure, water state, texture properties and water holding capacity (WHC) of MPG with different ADA additions were compared. The results showed that the shrimp MPG with 1% ADA addition had the highest breaking force and gel strength, WHC, and the densest three-dimensional network structure. The ADA had little significant effect on the secondary structure of MP and MPG. In addition, hydrogen and ionic bonds were the main chemical bonds of MP, while MPG is mainly dominated by hydrophobic and disulfide bonds. The correlation analysis of gel properties and water state of MPG showed that bound water and immobilized water had a positive effect on the gel strength.

Novel insights into the inhibitory mechanism of (+)-catechin against trimethylamine-N-oxide demethylase

Trimethylamine-N-oxide demethylase (TMAOase) is a key enzyme for the decomposition of trimethylamine oxide into formaldehyde. The study investigated the inhibitory effects of (+)-catechin on TMAOase and involved mechanism to minimize the formaldehyde (FA) content of seafood during storage. TMAOase was purified by DEAE-52 cellulose and Sephacryl S-300 chromatography and the inhibitory mechanism of TMAOase was studied by Lineweaver-Burk plots, fluorescence spectroscopy, and circular dichroism. Specific activity of 37 ± 0.7 U/mg was obtained with 205 -fold purification and 15% yield, and molecular mass was 25 kDa. (+)-Catechin was a reversible inhibitor of TMAOase and its induced mechanism was the non-competitive inhibition type. (+)-Catechin binding to TMAOase formed a complex with the binding constant (K_sv) of 0.72 × 10³ at 298 K. The formation of complex induced the static fluorescence quenching and changes in the conformation of TMAOase, leading to a reduction in the rate of catalysis.

Effect of the Partial Substitution of Sodium Chloride on the Gel Properties and Flavor Quality of Unwashed Fish Mince Gels from Grass Carp

Excessive salt is usually required to maintain good gel properties and quality characteristics for unwashed fish mince gels (UFMG). This study aimed to investigate the effects of partial sodium chloride substitution (30%) with different substitutes (potassium chloride, disodium inosine-5′-monophosphate, basil) on the gel and flavor properties of UFMG from Ctenopharyngodon idellus. The results indicated that the texture and gel strength of NK (30% NaCl was replaced with 30% KCl) were fairly similar to that of N group (NaCl only), and the whiteness had improved significantly (p < 0.05), while the product eventually yielded a certain bitter taste. The addition of disodium inosine-5′-monophosphate (DIMP) significantly (p < 0.05) increased the hardness, chewiness, buriedness degree of tryptophan and gel strength, decreased the content of α-helix structure in the gels, while less change occurred in gel whiteness and network structure. Basil significantly (p < 0.05) reduced the buriedness degree of tryptophan, gel strength and whiteness, and deteriorated the gel structure. Nevertheless, the addition of DIMP or basil reduced the bitterness induced by KCl and improved the overall acceptability scores of gels of the N group. Moreover, there was no distinct difference in moisture content and water-holding capacity between all groups. Therefore, replacing sodium chloride in UFMG with 25% potassium chloride and 5% DIMP may be an ideal sodium salt substitution strategy.

Effects of a cold plasma-assisted shrimp processing chain on biochemical and sensory quality alterations in Pacific white shrimps (Penaeus vannamei)

In this paper, remodeling the shrimp processing chain and the effects of the transformation on the biochemical and sensory qualities of fresh Pacific white shrimp (Penaeus vannamei) under refrigeration storage were investigated. In the proposed model, a dielectric barrier discharge atmospheric cold plasma pretreatment step using a 60 kV source for 60, 90, 120, and 150 s was introduced after the first and second wash followed by refrigeration storage at 4 ± 1 °C for 12 days. Chemical, biochemical, and sensory attributes of the shrimp were monitored and compared with those of shrimp processed through the traditional method without atmospheric cold plasma pretreatment (control). Incorporating minimal dielectric barrier discharge atmospheric cold plasma pretreatment step had more desirable quality outcomes characterized by low malondialdehyde concentration, low volatile nitrogen products content, and comparable proximate composition. Texture, pH, and color were remarkably retained at 120 and 150 s of atmospheric cold plasma pretreatment and protein degradation was negligible up to 90 s than at 120 and 150 s of pretreatment. We conclude that remodeling the shrimp processing chain through incorporating minimal dielectric barrier discharge atmospheric cold plasma pretreatment with key considerations on operation parameters can maximize the beneficial biochemical and sensory quality outcomes while minimizing the negative impacts associated with traditional shrimp processing.

Insight into the correlations among rheological behaviour, protein molecular structure and 3D printability during the processing of surimi from golden pompano (Trachinotus ovatus)

To investigate the 3D printability of surimi from golden pompano, the rheological properties, protein molecular structure, and 3D printability of food inks from every step of surimi processing were measured, and their correlations were analysed. The results showed that surimi from chopping (surimi-C), chopping with salt (surimi-CS) and setting (surimi-S) were suitable for 3D printing, among which surimi-CS had the best shape fidelity. The clustering analysis of variables revealed that the yield stress and A_F could be used as indexes to characterize extrusion and deposition behaviour of surimi, respectively. The accuracy of 3D printing was affected by the extrusion property of the food ink, which was controlled by the ionic bond content. The stability of 3D printing was affected by the self-supporting capacity of the food ink, which was controlled by the hydrogen bond and hydrophobic interaction contents. The results provided theoretical guidance for developing 3D printing of surimi ingredients.

Redox Proteomic Analysis Reveals Microwave-Induced Oxidation Modifications of Myofibrillar Proteins from Silver Carp (Hypophthalmichthys molitrix)

To provide an insight into the oxidation behavior of cysteines in myofibrillar proteins (MPs) during microwave heating (MW), a quantitative redox proteomic analysis based on the isobaric iodoacetyl tandem mass tag technology was applied in this study. MPs from silver carp muscles were subjected to MW and water bath heating (WB) with the same time-temperature profiles to eliminate the thermal differences caused by an uneven energy input. Altogether, 422 proteins were found to be differentially expressed after thermal treatments as compared to that with no heat treatment. However, MW triggered a larger number of proteins and cysteine sites for oxidation. Myosin heavy chain, myosin-binding protein C, nebulin, α-actinin-3-like, and titin were found to be highly susceptible to oxidation under microwave irradiation. Notably, MW caused such modifications at cysteine site 9 in the head of myosin, revealing the enhancement mechanism of MP gelation by excess cysteine cross-linking during microwave processing. Furthermore, Gene Ontology and functional enrichment analyses suggested that the two thermal treatments resulted in some differences in ion binding, muscle cell development, and protein-containing complex assembly. Overall, this study is the first to report the redox proteomic changes caused by MW and WB treatments, thus providing a further understanding of the microwave-induced oxidative modifications of MPs.

Effects of High Hydrostatic Pressure on the Conformational Structure and Gel Properties of Myofibrillar Protein and Meat Quality: A Review

In meat processing, changes in the myofibrillar protein (MP) structure can affect the quality of meat products. High hydrostatic pressure (HHP) has been widely utilized to change the conformational structure (secondary, tertiary and quaternary structure) of MP so as to improve the quality of meat products. However, a systematic summary of the relationship between the conformational structure (secondary and tertiary structure) changes in MP, gel properties and product quality under HHP is lacking. Hence, this review provides a comprehensive summary of the changes in the conformational structure and gel properties of MP under HHP and discusses the mechanism based on previous studies and recent progress. The relationship between the spatial structure of MP and meat texture under HHP is also explored. Finally, we discuss considerations regarding ways to make HHP an effective strategy in future meat manufacturing.

Starch-fatty acid complexes improve the gel properties and enhance the fatty acid content of Nemipterus virgatus surimi under high-temperature treatment

The effect of high amylose corn starch (HAS)-fatty acid complexes on the gel properties, protein secondary structure, microstructure, fatty acid content, and sensory properties of surimi under high-temperature treatment were investigated. The formation of HAS-fatty acid complexes increased melting temperature and decreased average particle size of HAS. The addition of HAS-fatty acid complexes significantly improved the breaking force, deformation and whiteness of surimi gels. The water in surimi gels containing HAS or HAS-fatty acid complexes became increasingly immobilized. HAS or HAS-fatty acid complexes promoted protein conformational transition from α-helix structure to other three secondary structure. Surimi gels added with HAS-fatty acid complexes had more compact network structure and higher fatty acid content. Moreover, the better sensory properties were obtained in surimi gels containing HAS-fatty acid complexes. Therefore, starch-fatty acid complexes not only could improve the gel properties of surimi, but also enhance its fatty acid content.

Recent developments in maintaining gel properties of surimi products under reduced salt conditions and use of additives

Salt is a necessary condition to produce a surimi product that is based on the gelation of salt-soluble myofibrillar proteins. Recently, there has been a growing concern among consumers to consume healthy foods due to the threat of several chronic diseases caused by an unhealthy diet. Methods of reducing salt content out of concern for health issues caused by excessive sodium intake may affect the gel properties of surimi, as can many health-oriented food additives. Several studies have investigated different strategies to improve the health characteristics of surimi products without decreasing gel properties. This review reports recent developments in this area and how the gel properties were successfully maintained under reduced-salt conditions and the use of additives. This review of recent studies presents a great deal of progress made in the health benefits of surimi and can be used as a reference for further development in the surimi product processing industry.

In Situ Measurement Methods for the CO2-Induced Gelation of Biopolymer Systems

This work presents two novel methods to investigate in situ the carbon dioxide (CO₂)-induced gelation of biopolymer-based solutions. The CO₂-induced gelation is performed in a viewing cell at room temperature under CO₂ pressure (20 to 60 bar), whereby calcium precursors are used as cross-linkers. The novel methods allow the in situ optical observation and evaluation of the gelation process via the change in turbidity due to dissolution of dispersed calcium carbonate (CaCO₃) particles and in situ pH measurements. The combination of both methods enables the determination of the gelation direction, gelation rate, and the pH value in spatial and temporal resolution. The optical gelation front and pH front both propagate equally from top to bottom through the sample solutions, indicating a direct link between a decrease in the pH value and the dissolution of the CaCO₃ particles. Close-to-vertical movement of both gelation front and pH front suggests almost one dimensional diffusion of CO₂ from the contact surface (gel–CO₂) to the bottom of the sample. The gelation rate increases with the increase in CO₂ pressure. However, the increase in solution viscosity and the formation of a gel layer result in a strong decrease in the gelation rate due to a hindrance of CO₂ diffusion. Released carbonate ions from CaCO₃ dissolution directly influence the reaction equilibrium between CO₂ and water and therefore the change in pH value of the solution. Increasing the CaCO₃ concentrations up to the solubility results in lower gelation rates.

The Effect of Age on the Myosin Thermal Stability and Gel Quality of Beijing Duck Breast

The effect of age (22, 30, 38, and 46 days) on Beijing duck breast myosin gels was investigated. The results showed that the water holding capacity (WHC) and gel strength were markedly improved at the age of 30 days. Differential scanning calorimetry suggested that the myosin thermal ability increased at the age of 30 and 38 days (p<0.05). A compact myosin gel network with thin cross-linked strands and small regular cavities formed at the age of 30 days, which was resulted from the higher content of hydrophobic interactions and disulfide bonds. Moreover, the surface hydrophobicity of myosin extracted from a 30-day-old duck breast decreased significantly under temperature higher than 80°C (p<0.05). This study illustrated that myosin extracted from a 30-day-old duck’s breast enhanced and stabilized the WHC, thermal stability and molecular forces within the gel system. It concluded that age is an essential influencing factor on the myosin thermal stability and gel quality of Beijing duck due to the transformation of fibrils with different myosin character.

Stability of trypsin inhibitor isolated from potato fruit juice against pH and heating treatment and in vitro gastrointestinal digestion

Potato trypsin inhibitor (PTI) was obtained from imitated potato wastewater through a sustainable method of sequential acid precipitation, salting out, and ultrafiltration. PTI had a favorable inhibition with the low IC₅₀ of 6.861 ± 0.107 mg/L. To explore stability of PTI against pH and heating treatment, PTI secondary structure was investigated by circular dichroism and inhibition was determined using the BAPNA method. The results indicated that PTI exerted a certain heat resistance and excellent stability over a wide pH range. Also, correlation analysis displayed β-sheet and β-turn contents of PTI had a positive correlation with inhibition, whereas α-helix and random coil contents were negatively correlated with inhibition. During in vitro digestion, the limited loss rate of activity (29.28%) and degree of hydrolysis (24.39%) suggested that PTI presented sufficient resistance to gastrointestinal digestion. These findings would extend beneficial hints to convert potato wastewater by-product into the potential anti-obesity ingredient in future.

Gel properties of Amur sturgeon (Acipenser schrenckii) surimi improved by lecithin at reduced and regular-salt concentrations

This study examined the gel properties of Acipenser schrenckii (A. schrenckii) surimi with 10 and 30 g kg⁻¹ of added lecithin at reduced-salt (3 g kg⁻¹ NaCl) and regular-salt (30 g kg⁻¹ NaCl) concentrations. The results suggested that the gel properties of A. schrenckii surimi were strongly salt-dependent. Notably, regular-salt surimi gels showed better properties than reduced-salt surimi in all analyses. However, with the addition and increased levels of lecithin, the hydrogen bond formation and β-sheet content of low-salt surimi gels significantly increased (P < 0.05). The rheological patterns demonstrated higher elasticity and the gel strength, textural properties, and water holding capacity were also enhanced by lecithin (P < 0.05). The SEM analysis showed that the protein formation induced by lecithin was able to fill the empty voids and reinforce the microstructures. Unlike in reduced-salt surimi, the influence of higher salt concentration was more dominant in regular-salt surimi diminishing the effects of lecithin. The only adverse effect of lecithin found in this study was the decreasing of whiteness, especially when lecithin added up to 3% in both salt conditions. However, there was no significant damage to the overall gel properties.

This study examined the gel properties of Acipenser schrenckii (A. schrenckii) surimi with 10 and 30 g kg⁻¹ of added lecithin at reduced-salt (3 g kg⁻¹ NaCl) and regular-salt (30 g kg⁻¹ NaCl) concentrations.

Correlation Between the Water Solubility and Secondary Structure of Tilapia-Soybean Protein Co-Precipitates

The secondary structure of a protein has been identified to be a crucial indicator that governs its water solubility. Tilapia protein isolate (TPI), soybean protein isolate (SPI), and tilapia-soybean protein co-precipitates (TSPC_3:1, TSPC_2:1, TSPC_1:1, TSPC_1:2, and TSPC_1:3) were prepared by mixing tilapia meat and soybean meal at different mass ratios. The results demonstrated that the water solubility of TSPCs was significantly greater than that of TPI (p <0.05). The changes in ultraviolet–visible and near-ultraviolet circular dichroism spectra indicated that the local structure of TSPCs was different from that of TPI and SPI. Fourier transform infrared Spectroscopy revealed the co-existence of TPI and SPI structures in TSPCs. The secondary structures of TSPCs were predominantly α-helix and β-sheet. TSPC_1:1 was unique compared to the other TSPCs. In addition, there was a good correlation between the water solubility and secondary structure of TSPCs, in which the correlation coefficients of α-helix and β-sheet were −0.964 (p <0.01) and 0.743, respectively. TSPCs displayed lower α-helix contents and higher β-sheet contents compared to TPI, which resulted in a significant increase in their water solubility. Our findings could provide insight into the structure–function relationship of food proteins, thus creating more opportunities to develop innovative applications for mixed proteins.

Changes to the tropomyosin structure alter the angiotensin-converting enzyme inhibitory activity and texture profiles of eel balls under high hydrostatic pressure

Changes in the structure of tropomyosin (TM) altered the texture profiles of eel balls and the inhibitory activity of the angiotensin-converting enzyme (ACE). The secondary and tertiary structure of TM was determined after high hydrostatic pressure (HHP) treatment. The correlation between the spatial structure of TM and the texture profiles of eel balls was developed and discussed. The β-sheet was converted to a β-turn and a random coil when treated at HHP (200-400 MPa), meanwhile the α-helix unfolded and was converted into a β-sheet, β-turn and a random coil with treatment at 500 and 600 MPa. The surface hydrophobicity (H0) was increased and the sulfhydryl (SH) content decreased with an increase in the pressure. The results indicated that the texture profiles of eel balls showed a negative relationship with the α-helix, β-sheet and SH content. The texture profiles of eel balls were greatly enhanced after treatment at 500 and 600 MPa, leading to the improved surface network of the eel ball products. The ACE inhibitory activity of TM after HHP treatment exhibited a positive relationship with the β-sheet content in the protein. The ACE inhibitory activity was preserved under 600 MPa.