Effects of microbial transglutaminase on gel formation of frozen-stored longtail southern cod (Patagonotothen ramsayi) mince

Rice bran oil-in-water emulsion stabilized by Amur catfish myofibrillar protein: Characteristics and its application in surimi gels

The objective of this investigation was to isolate amur catfish myofibrillar protein (AMP), emulsify it with rice bran oil, and assess its application in the silver carp surimi gel. The proportion and addition of AMP/rice bran oil emulsion on the gel properties were compared. The emulsion stabilized by 3 % AMP was stable when an oil/water ratio of 0.70 and 0.75 was employed, as evidenced by its appearance, microstructure, and rheological characteristics. The L*, a* and whiteness values of gels observably elevated when the emulsion blended (p < 0.05). The mechanical capacities (texture and rheology indicators) of surimi gels were dramatically improved with 5 % emulsion added (p < 0.05). However, the addition of excessive emulsion (up to 15 %) impeded the formation of surimi protein network and lowered water retention ability of surimi gels. Moreover, 5 % emulsion was distributed uniformly throughout the gel matrix, giving rise to the development of a dense and uniform network with high water binding capacity. Furthermore, the study on protein solubility expressed that the addition of the emulsion facilitated protein-protein interactions in surimi gels. In summary, the addition of 5 % AMP stabilized rice bran oil emulsion could yield a stronger surimi gel with increased whiteness. The resulting gels could serve as healthy fat-rich surimi-based products.

Effects of different protein cross-linking degrees on physicochemical and subsequent thermal gelling properties of silver carp myofibrillar proteins sol subjected to freeze-thaw cycles

Knowledge regarding the denaturation process and control methods for depolymerized sol-state myofibrillar proteins (MPs) during freezing remains scant. This study investigated the effects of protein cross-linking treatment before freezing on physicochemical and subsequent gelation properties of MPs sol subjected to freeze-thaw (F-T) cycles. Results indicated that after five F-T cycles, cross-linked MPs sols showed increased high molecular weight polymers and bound water (T21a and T21b) mobility, suggesting enhanced protein-protein interactions at the expense of protein-water interactions. Upon heating after F-T cycles, gels formed from cross-linked sols exhibited significantly higher hardness, springiness, and cooking loss (P < 0.05), alongside more contracted gel networks. Correlation analysis revealed that the formation and properties of thermal gel after freezing closely relate to changes in molecular conformation and chemical bonds of cross-linked MPs sol during freezing. This study provides new insights into regulating the freezing stability and post-thawed thermal processing properties of sol-based surimi products.

Improvement of Surimi Gel from Frozen-Stored Silver Carp

Silver Carp (SC) is an under-utilized, invasive species in North American river systems. In this study, the synergistic effects of manufactured Microfiber (MMF), Transglutaminase (TG), and chicken skin collagen (CLG)) to enhance surimi gel quality from frozen SC were studied. The gel strength, textural properties, rheological properties, water-holding capacity (WHC), water mobility, microstructure, and protein composition of the gel samples were determined to assess the impact of the additives individually and synergistically. The results suggested that TG had the most pronounced effect on the surimi gel properties by promoting protein cross-linking. Synergistic effects between TG, MMF, and CLG can bring effective gel property enhancement larger than the individual effect of each additive alone. With the established response-surface models, the combination of CLG and MMF can be optimized to produce surimi gels with less TG but comparable in properties to that of the optimal result with high TG usage. The findings of this study provided a technical foundation for making high-quality surimi gel products out of frozen-stored SC with synergistic utilization of additives, which could serve as guidelines for the industrial development of new surimi products.

Enhancing gel behavior of yellow croaker surimi by fruit extracts: Physicochemical properties and molecular mechanism

The aim of this study was to investigate the effects of grape seed extract (GSE), acerola cherry extract (ACE), and blueberry extract (BBE) on the physicochemical properties and structure of the yellow croaker surimi gel. In addition, molecular docking and molecular dynamics (MD) simulation were utilized to study the binding mechanism of yellow croaker's fibrillin and fruit extracts. Surimi gel with 1.5% GSE, ACE, and BBE had the highest water holding capacity, hardness, chewability, cohesion, breaking force, breaking distance, gel strength, and densest 3D network structure, according to the experiment's findings. Nevertheless, the cross-linking of proteins in surimi was blocked with the further increase of fruit extract (1.5%-2.0%), and the existing network of surimi was weakened or even destroyed. Three fruit extracts had little effect on the secondary structure of the surimi gel. Besides, hydrophobic and disulfide bonds are the main chemical bonds of croaker surimi. Molecular docking showed that B-type procyanidine (BP) interacted with ASN-183, SER-571, ASP-525, ARG-350, LYS-188, GLU-349, CYS-353, and other active amino acids in croaker protein. Moreover, it can form strong hydrogen bond interaction with ASN-183, SER-571, ASP-525, and ARG-350 at the active sites of protein. The BP-Larimichthys crocea protein system's MD simulation was carried out, and calculations for the simulation's root mean square deviation, root mean square fluctuation, radius of gyration, solvent accessible surface area, and hydrogen bonds were made. It was found that these indices can demonstrate that the BP binding contributes to the stability of the yellow croaker structure.

Progress in the application of novel cryoprotectants for the stabilization of myofibrillar proteins

In this review, the physicochemical and conformational changes of myofibrillar proteins (MPs) of freeze-induced mince-based aquatic foods were comprehensively summarized in depth. Studies have demonstrated that temperature fluctuation and long-time freezing negatively affect food quality, resulting in texture alteration, drip fluid, flavor degradation, and nutrition loss due to MPs denaturation, aggregation, and oxidation. Attempts have been made in ice-recrystallization inhibition, freezing point depression, and ice shape and growth control for better cryopreservation. Moreover, to further minimize the quality deterioration, cryoprotectants were acknowledged to reduce the denaturation and aggregation of the MPs effectively. Recently, interest in novel functional ingredients, including oligosaccharides, protein hydrolysates, and natural polyphenols demonstrated excellent cryoprotective effects while avoiding health concerns and undesirable flavor caused by traditional sugar-based or phosphates-based cryoprotectants. Therefore, the present review provides a systematic overview of these low molecular weight multifunctional substances with a particular sequence and highlights their underlying mechanism in the inhibition of ice recrystallization the stabilization of MPs.

Microbial Transglutaminase Cross-Linking Enhances the Textural and Rheological Properties of the Surimi-like Gels Made from Alkali-Extracted Protein Isolate from Catfish Byproducts and the Role of Disulfide Bonds in Gelling

The texture of surimi-like gels made from the protein isolate extracted from catfish byproducts has been proven to be brittle and lack elasticity. To address this issue, varying levels of microbial transglutaminase (MTGase) from 0.1 to 0.6 units/g were applied. MTGase had little effect on the color profile of gels. When MTGase at 0.5 units/g was employed, hardness, cohesiveness, springiness, chewiness, resilience, fracturablity, and deformation were increased by 218, 55, 12, 451, 115, 446, and 71%, respectively. A further increase in added MTGase did not lead to any textural improvement. In comparison to the gels made from fillet mince, the gels made from protein isolate were still lower in cohesiveness. Due to the activated endogenous transglutaminase, a setting step enhanced the textural properties of gels made from fillet mince. However, because of the endogenous proteases-induced protein degradation, the setting step led to a texture deterioration of the gels made from protein isolate. Gels made from protein isolate showed 23-55% higher solubility in reducing solution than in non-reducing solution, suggesting the vital role of disulfide bonds in the gelation process. Due to the different protein composition and conformation, fillet mince and protein isolate exhibited distinct rheological properties. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed the highly denatured protein isolate was susceptible to proteolysis and prone to disulfide formation during the gelation process. It also revealed that MTGase had an inhibitory effect on the proteolysis induced by endogenous enzymes. In view of the susceptibility of the protein isolate to proteolysis during gelation, future research should consider including other enzyme inhibitory agents in the presence of MTGase to improve the gel texture.

Effects of partial replacement of unwashed Antarctic krill surimi by Litopenaeus vannamei surimi on the heat-induced gelling and three-dimensional-printing properties

There is an emerging consumption of the Antarctic krill (AK) muscle-based food due to its excellent nutritional value and enormous biomass storage capacity. However, the coarse texture of the muscle and the weak gelling properties of AK protein impede its expansion in surimi-based products. This investigation successfully prepared heat-induced gels of AK surimi with desirable textural properties by including Litopenaeus vannamei in varying proportions. Higher concentrations of L. vannamei resulted in improved three-dimensional printability, greater water-holding capacity (WHC), larger viscoelastic modulus, and a well-formed microstructural matrix of AK surimi, due to an increased level of myofibrillar protein. Compared with AK, L. vannamei muscle had double the salt-soluble protein content, which was corroborated by increased intensity of bands of actin, paramyosin, tropomyosin, and myosin light chains on reducing SDS-PAGE. DSC results indicated that a high ratio of L. vannamei elevated the denaturation temperature and enthalpy of myosin, sarcoplasmic protein, and actin, suggesting a high degree of cross-linking. It was also found that when hydroxypropyl cassava starch was added at 0.5% (w/w), WHC and gel strength were further improved with a more compact gel matrix. The successful preparation of unwashed mixed surimi with AK meat fully exploited in this study provides an option for AK surimi-based product industrialization.

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.

Gelation properties and protein conformation of Grass Carp fish ball as influenced by egg white protein

Dried egg white powder (EWP) and purified ovalbumin (OVA, 98%) were used as supplements to improve grass carp (GC) fish balls (FB) quality. The effects of EWP and/or OVA contents on the gel strength, water holding capacity (WHC), moisture migration and distribution, and rheological properties of GC-FB, as well as on myofibrillar protein (MfP) structures in the GC-FB were evaluated. The results showed that with the increase of EWP addition from 0 to 4% (w/w), the gel strength and WHC of the GC-FB samples were increased from 34.28 to 66.63 N×mm, and 83.02 to 88.36%, respectively, but the increases were insignificant between 3% and 4% EWP-added GC-FBs (p>0.05). As the EWP increased, the T₂ relaxation time shifted towards lower values, indicating a general decline in water mobility. The effects of EWP on rheological properties were insignificant. Addition of OVA and/or EWP led to changes in secondary structural units in the FB, with α-helix (27.53%) reaching the highest value in OVA-added GC-FB, β-sheet (46.07%) reaching the highest value in GC-FB, and β-turn (33.54%) reaching the highest value in EWP-added GC-FB, respectively. Raman spectroscopy revealed that OVA-added GC-FB had the lowest hydrophobic interlinkages. Protein pattern analysis suggested that the OVA (1.58%) might contribute to the decrease in the myosin heavy chain (MHC) band intensity through cross-linked with MfP. These results suggested that EWP could improve the quality of GC-FBs and OVA played an important role with MfP gelation. This article is protected by copyright. All rights reserved.

Roles of Proteins/Enzymes from Animal Sources in Food Quality and Function

Animal proteins are good sources of protein for human, due to the composition of necessary amino acids. The quality of food depends significantly on the properties of protein inside, especially the gelation, transportation, and antimicrobial properties. Interestingly, various kinds of molecules co-exist with proteins in foodstuff, and the interactions between these can significantly affect the food quality. In food processing, these interactions have been used to improve the texture, color, taste, and shelf-life of animal food by affecting the gelation, antioxidation, and antimicrobial properties of proteins. Meanwhile, the binding properties of proteins contributed to the nutritional properties of food. In this review, proteins in meat, milk, eggs, and fishery products have been summarized, and polysaccharides, polyphenols, and other functional molecules have been applied during food processing to improve the nutritional and sensory quality of food. Specific interactions between functional molecules and proteins based on the crystal structures will be highlighted with an aim to improve the food quality in the future.

Characteristic thermal denaturation profile of myosin in the longitudinal retractor muscle of sea cucumber (Stichoupus japonicas)

This study elucidated thermal denaturation profile of myosin in sea cucumber longitudinal muscle. Sea cucumber myosin structure was different from fish at its head/tail junction which could not be cleaved by EDTA. However, sea cucumber myosin in salt-dissolved form could be cleaved into heavy meromyosin (HMM) and light meromyosin (LMM) segments. Although sea cucumbers lived in cold water, its myosin stability was comparable to tropical tilapia, more stable than rainbow trout (a cold water fish). Upon heating, the sea cucumber myosin lost its salt-solubility rapidly, even before losing its ATPase activity. The quick loss of salt-solubility suggested a quick denaturation at light meromyosin region as revealed by chymotryptic digestion. These results suggested that sea cucumber myosin is consisted of very stable head region and unstable tail region, which is important for choosing proper heating conditions for sea cucumber processing.