Effects of chitosan and sodium alginate active coatings containing ε-polysine on qualities of cultured pufferfish (Takifugu obscurus) during cold storage

Effects of atmospheric cold plasma treatment mode on muscle quality and bacterial community of red shrimp during cold storage

Atmospheric cold plasma (ACP), known for its safety, non-thermal processing, and energy efficiency, is especially effective for preserving perishable items such as seafood. However, excessive use of ACP may cause oxidation and sensory quality deterioration, which limits its application in the seafood industry. Thus, optimizing ACP treatment modes to balance sterilization efficiency with minimal oxidative effects is essential. This study aims to explore the impact of different ACP treatment modes (cyclical and one-time treatment) on the muscle quality and bacterial community of red shrimp during cold storage. The results indicated that on day 0 of storage, compared to the blank group and the one-time treatment group, the cyclical treatment significantly reduced the total viable count in red shrimp (p < 0.05). However, no significant differences were observed in centrifugal loss, cooking loss, textural properties, total sulfhydryl content, or Ca2+-ATPase activity (p > 0.05). By day 8, both ACP treatment modes significantly improved the protein quality of red shrimp. Compared with the one-time treatment, cyclical treatment reduced the abundance of Aliivibrio (57.24 %), Pseudoalteromonas (97.34 %), and Psychrobacter (59.07 %) in the bacterial community and delayed bacterial succession (especially Aliivibrio salmonicida, Psychrobacter cibarius, and Pseudoalteromonas nigrifaciens), slowing down the degradation of protein quality. Specifically, in the cyclical treatment group, cooking loss was reduced by 7.01 %, and improvements were observed in hardness, total sulfhydryl content, and Ca2+-ATPase activity, which increased by 8.93 %, 17.54 %, and 5.63 %, respectively. Overall, this study demonstrates that the ACP cyclical treatment mode has greater potential in preserving the freshness of seafood.

Changes in flavor quality of marinated Chinese mitten crab (Eriocheir sinensis) with vacuum pack during cold storage

In order to study the pattern of changes in quality of marinated Chinese mitten crabs (Eriocheir sinensis) during cold storage, three aspects of sensory, taste and odor were investigated. Sensory evaluation and total volatile basic nitrogen (TVB-N) were measured in viscera and abdomen muscle at 0, 7, 15 and 30 days of storage at 4°C. Sensory scores significantly declined at 15 d, coinciding with TVB-N levels exceeding 25 mg N/100 g. Taste profiling demonstrated distinct changes over the storage period. Arginine (Arg) in viscera and abdomen muscle decreased by 18.16 % and 43.26 %, respectively, while adenosine monophosphate (AMP) dropped to 48.46 and 22.22 mg/100 g after 15 days, contributing to loss of umami. Based on the correlation analysis, it was known that bitterness was related to freshness, with tyrosine (Tyr), phenylalanine (Phe), hypoxanthine (Hx) and hypoxanthine riboside (HxR) being more significant contributors to the bitterness. Gas chromatography-ion mobility spectrometry (GC-IMS) analysis attributed late-stage undesirable odors to the production of aldehydes and ketones, particularly heptanone, 3-hydroxy-2-butanone, heptanal and glutaraldehyde. This study provided valuable guide for improving the flavor quality of Chinese mitten crabs in the field of prepared dish.

Establishment and characterization of a fin cell line from Takifugu obscurus and its application to fish immunology

Takifugu obscurus (pufferfish) is an important species in aquaculture and has become widely popular in China and Japan. However, the development of the pufferfish aquaculture industry has been significantly impacted by severe diseases. Fish cell lines, as a model for in vitro studies, have the advantages of low cost, easy culture, and low genetic variation rate. A novel cell line from the fin of T. obscurus was established in this study and named TOF. TOF grew optimally with L-15 medium at 28°C and showed a multipolar fibroblast-like morphology. Mitochondrial cytochrome oxidase subunit 1 (COI) gene identification and karyotype detection confirmed that TOF cells originated from T. obscurus and the chromosome number was 44 (2n = 44). Transfection experiments showed that TOF cells were able to transfect and express exogenous genes by lipofection and electroporation. The studies of salinity (NaCl) and alkalinity (NaHCO3) on TOF proliferation showed that the highest multiplication rate of TOF was obtained at 6‰ NaCl mass and 4 g/L alkalinity, respectively. Furthermore, the expressions of several genes associated with the immune response were significantly upregulated after stimulating TOF cells with lipopolysaccharide (LPS) and poly (I:C), including irf7, il10, myd88, and nod1. Additionally, the Aeromonas hydrophila infection assay with TOF cells showed that TOF cells were sensitive to bacteria, and pufferfish could promote antimicrobial activity through NLR/NF-κB pathway to regulate the production of cytokines. This study suggested that TOF cell line could be an advantageous in vitro model for the investigation of fish immunology and virology, and could assist us to better comprehend the T. obscurus immune response to bacterial invasion.

Stability of large yellow croaker (Pseudosciaena crocea) as affected by temperature abuse during frozen storage: Quality attributes, myofibril characteristics, and microstructure

Temperature abuse occurs frequently during transportation and frozen storage, which affects the quality of frozen aquatic products. Recrystallization generated by temperature abuse leads to irreversible damage to the muscle tissue and microstructure, and exacerbates undesirable oxidation reactions, thus reducing the quality of frozen aquatic products. In this study, a modeling system of temperature abuse alternating between -24 °C and -7 °C was established to evaluate the effect of temperature abuse on the stability of frozen large yellow croaker. The results revealed that temperature abuse caused water migration with the extension of storage time, as well as poorer texture, color, and freshness. Furthermore, the structure of myofibrillar protein (MP) was severely damaged, with a gradual decrease in total sulfhydryl groups and Ca2+-ATPase activity, a loosening of the secondary structure, and a disruption of the protein conformation. The confocal laser scanning microscopy (CLSM) analysis also found that temperature abuse exacerbated protein aggregation. Therefore, temperature abuse during transportation and frozen storage could affect the stability of large yellow croaker negatively, and it mainly originated from the growth of ice crystals and the effect of recrystallization. The study was supposed to provide new insights into the improvement of frozen aquatic products quality.

Effects of slightly acidic electrolyzed water combined with ԑ-polylysine-chitooligosaccharide Maillard reaction products treatment on the quality of vacuum packaged sea bass (Lateolabrax japonicas)

In this study, a new natural preservative, ε-polylysine (ε-PL) and chitooligosaccharides (COS) Maillard reaction products (LC-MRPs), was prepared by Maillard reaction. The preservation effect of LC-MRPs combined with slightly acidic electrolyzed water (SAEW) pretreatment (SM) on vacuum-packed sea bass during refrigerated storage was evaluated. The results showed that after 16 days, SM treatment could effectively inhibit the microbial growth and prevent water migration in sea bass. In addition, the highest water holding capacity (69.79 %) and the best sensory characteristics, the lowest malonaldehyde (MDA) (58.96 nmol/g), trimethylamine (TMA) (3.35 mg/100 g), total volatile basic nitrogen (TVB-N) (16.93 mg N/100 g), myofibril fragmentation index (MFI) (92.2 %) and TCA-soluble peptides (2.16 μmol tyrosine/g meat) were related to SM group. Combined with sensory analysis, we can conclude that the combined treatment of SAEW and LC-MRPs could prolong the shelf-life of sea bass for another 11 days compared with the DW group. Results disclosed that the composite treatment of SAEW and LC-MRPs is a promising technology to improve the shelf-life of vacuum-packed sea bass during refrigerated storage.

Design and optimization of ε-poly-l-lysine with specific functions for diverse applications

ε-Poly-l-lysine (ε-PL) is a natural homo-poly(amino acid) which can be produced by microorganisms. With the advantages in broad-spectrum antimicrobial activity, biodegradability, and biocompatibility, ε-PL has been widely used as a preservative in the food industry. Different molecular architectures endow ε-PL and ε-PL-based materials with versatile applications. However, the microbial synthesis of ε-PL is currently limited by low efficiencies in genetic engineering and molecular architecture modification. This review presents recent advances in ε-PL production and molecular architecture modification of microbial ε-PL, with a focus on the current challenges and solutions for the improvement of the productivity and diversity of ε-PL. In addition, we highlight recent examples where ε-PL has been applied to expand the versability of edible films and nanoparticles in various applications. Commercial production and the challenges and future research directions in ε-PL biosynthesis are also discussed. Currently, although the main use of ε-PL is as a food preservative, ε-PL and ε-PL-based polymers have shown excellent application potential in biomedical fields. With the development of synthetic biology, the design and synthesis of ε-PL with a customized molecular architecture are possible in the near future. ε-PL-based polymers with specific functions will be a new trend in biopolymer manufacturing.

Food off-odor generation, characterization and recent advances in novel mitigation strategies

The pronounced perception of off-odors poses a prevalent issue across various categories of food ingredients and processed products, significantly exerting negative effects on the overall quality, processability, and consumer acceptability of both food items and raw materials. Conventional methods such as brining, marinating, and baking, are the main approaches to remove the fishy odor. Although these methods have shown notable efficacy, there are simultaneously inherent drawbacks that ultimately diminish the processability of raw materials, encompassing alterations in the original flavor profiles, the potential generation of harmful substances, restricted application scopes, and the promotion of excessive protein/lipid oxidation. In response to these challenges, recent endeavors have sought to explore innovative deodorization techniques, including emerging physical processing approaches, the development of high-efficiency adsorbent material, biological fermentation methods, and ozone water rinsing. However, the specific mechanisms underpinning the efficacy of these deodorization techniques remain not fully elucidated. This chapter covers the composition of major odor-causing substances in food, the methodologies for their detection, the mechanisms governing their formation, and the ongoing development of deodorization techniques associated with the comparison of their advantages, disadvantages, and application mechanisms. The objective of this chapter is to furnish a theoretical framework for enhancing deodorization efficiency through fostering the development of suitable deodorization technologies in the future.

Integrated volatile compounds and non-targeted metabolomics analysis reveal the characteristic flavor formation of proteins in grouper (Epinephelus coioides) during cold storage

Microorganisms, lipids, and proteins always interact in a complex way in the fish matrix, which becomes a hindrance to evaluate the quality of the individual factors affecting them. In order to investigate the relationship between protein deterioration and volatile compounds (VOCs) in grouper during cold storage, the myofibril protein (MP) was used as a single-factor study to exclude microorganisms and lipids effects. The oxidation and degradation of MP during storage at 4 ℃ were evaluated, including MP content, total sulfhydryl content, carbonyl content, spatial structure and microstructure. Headspace-solid phase microextraction- gas chromatography-mass spectrometry (HS-SPME-GC-MS) was used to analyze the VOCs of grouper MP, and a total of 7 key VOCs were selected, including three ketones (2-nonanone, 2-undecanone and 2-tridecanone), three esters (methyl butyrate, methyl palmitate and methyl ester 9-octadecenoic acid) and one alcohol (3-methyl-1-butanol). At the same time, a non-targeted metabolomics method based on UPLC-Q-Extractive Orbitrap was used to investigate the changes in metabolites during MP storage. A total of 107 up-regulated differential metabolites and 7 down-regulated metabolites were annotated, and 6 metabolic pathways highly related to proteins were screened. Spearman correlation analysis showed that 7 key VOCs are associated with the biosynthesis and metabolism of ornithine and lysine. And a possible solution to protein deterioration in grouper was proposed, which provided a reference for improving protein quality and regulating flavor formation during cold storage of grouper at source.

Evaluation on the effect of ice glazing with different compound additives on the quality of frozen stored (-23 °C) large yellow croaker (Pseudosciaena crocea)

BACKGROUND

Compounded ice glazing has been used in large yellow croaker to improve its quality during frozen storage. The ice glazing liquid is prepared by compound use of trehalose and tea polyphenols, and the moisture, protein-related properties and freshness of the fish have been evaluated during 300 days of frozen storage.

RESULTS

The results showed that the addition of trehalose effectively reduced the loss of water. At the same time, it was difficult for ice crystals to grow under the action of trehalose, the average diameter could still be maintained at 111.25-119.85 μm. The combination with tea polyphenols could effectively maintain the protein structure and keep the total volatile base nitrogen (TVB-N) and K value within 11.84 mg/100 g and 13.18%, so that the freshness of the fish was always at the first level.

CONCLUSION

In a word, the ice glazing with 5% trehalose and 8% tea polyphenols had the best preservation effect, which was recommended for the frozen storage. © 2022 Society of Chemical Industry.

Effect of Nanoemulsion Containing Enterocin GR17 and Cinnamaldehyde on Microbiological, Physicochemical and Sensory Properties and Shelf Life of Liquid-Smoked Salmon Fillets

The spoilage of liquid-smoked salmon represented a serious restriction for shelf life, due to the loss of taste, smell, color and consistency in product quality. The objective of this study was to investigate the feasibility of applying a nanoemulsion delivery system co-encapsulated enterocin Gr17 and essential oils (EOs) to the refrigerated storage of liquid-smoked salmon. The synergistic inhibiting effects of enterocin Gr17 and EOs were evaluated, a nanoemulsion delivery system with the optimal combination was developed, and the evolution of the microbiological, physicochemical, and sensory properties of liquid-smoked salmon fillets were analyzed during a 49-day period of refrigerated storage. The results showed that the combination of enterocin Gr17 and cinnamaldehyde essential oil (CEO) displayed the strongest synergistic inhibiting effect on foodborne pathogens. A nanoemulsion system incorporating enterocin Gr17 and CEO was successfully developed and presented a broad spectrum of activity against most of the tested bacteria. A nanoemulsion system incorporating enterocin Gr17 and CEO (CO-NE) could significantly inhibit the growth of microflora, suppress the accumulation of total volatile basic nitrogen (TVB-N) and thiobarbituric acid reactive substance (TBARS), and maintain better color, texture, and sensory profiles during smoked salmon storage at 4 °C. Overall, from a microbiological, physicochemical, and sensory point of view, the CO-NE treatment could extend the shelf life to 42 days and maintain the relatively low TVB-N value (≤15.38 mg/100 g), TBARS value (≤2.51 mg MDA/kg), as well as a relatively high sensory score (≥5.83) during the whole storage period. Hence, a nanoemulsion system incorporating enterocin Gr17 and CEO could be a promising bio-preservative technology and alternative to the conventional processes used for improving the safety and quality of chilled liquid-smoked salmon.

Effects of single-, dual-, and multi-frequency ultrasound-assisted freezing on the muscle quality and myofibrillar protein structure in large yellow croaker (Larimichthys crocea)

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MUAF significantly promoted the freezing process of large yellow croakers.

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MUAF enhanced the quality of large yellow croakers.

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MUAF better maintained the stability of fish protein.

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The mechanisms of single-, dual-, and multi-frequency UAF were analyzed.

Ultrasound-assisted freezing (UAF) has been proved to be a new technology to improve the quality of frozen foods. Frequency is an important parameter affecting UAF result. This study was to investigate the effects of single-, dual- and multi-frequency UAF on muscle quality and myofibrillar protein structure in large yellow croaker (Larimichthys crocea), providing reference for the application of multi-frequency UAF in frozen foods. Multi-frequency UAF increased the freezing rate and had lower thawing loss, thiobarbituric acid reactive substances (TBARS) value, total volatile basic nitrogen (TVB-N) value, and higher immobilized water content. Multi-frequency UAF had lower carbonyl, higher sulfhydryl content, and more stable myofibrillar protein secondary and tertiary structures. Confocal laser scanning microscopy (CLSM) indicated that the filamentous polymer in muscle fibrin solution with multi-frequency UAF was transformed into more evenly distributed units. In general, multi-frequency UAF significantly improved the freezing rate, reduced lipid oxidation, and maintained the myofibrillar structure.

Effects of starch/polyvinyl alcohol active film containing cinnamaldehyde on the quality of large yellow croaker (Pseudosciaena crocea) proteins during frozen storage

This study aimed to investigate the effects of starch/polyvinyl alcohol (starch/PVA) film containing cinnamaldehyde (CIN) with different humidity treatment on the quality changes of large yellow croaker (Pseudosciaena crocea) under vacuum packaging during frozen storage. It was evaluated by measuring the water loss, water migration, total volatile basic nitrogen (TVB-N), thiobarbituric acid (TBA), free amino acids (FAA) content, myofibril secondary and tertiary structure and microstructure of large yellow croaker. Compared with control group, the starch/PVA films could inhibit the water loss, water migration, protein degradation, lipid oxidation and microstructure damage of fish. The film containing CIN with higher humidity treatment showed the best protective effect for large yellow croaker. The film with higher humidity treatment showed better to maintain the quality of fish than that with low humidity treatment. Therefore, starch/PVA active film containing CIN with high humidity treatment showed good fresh-keeping potential in the frozen storage of aquatic products.

Antimicrobial Effect of Epigallocatechin Gallate Against Shewanella putrefaciens ATCC 8071: A Study Based on Cell Membrane and Biofilm

The study was to evaluate the antimicrobial impacts and biofilm influences on epigallocatechin gallate (EGCG) against Shewanella putrefaciens ATCC 8071. The minimum inhibitory concentration (MIC) of EGCG on S. putrefaciens was 160 μg mL^-1. The growth curve exhibited that EGCG had a good antimicrobial activity. EGCG caused damages to the bacterial cell wall and membrane based the intracellular component leakage and cell viability analysis. The damage to the membrane integrity by EGCG has been confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM shows deformation of shape, TEM shows cell membrane and wall damage, and the leakage of cytoplasmic material. The treatment with EGCG at 0.25× and 0.5× MIC resulted in decreased motility and elevated levels of oxidative stress, leading to an increase in biofilm formation. These results demonstrated that EGCG may be used as a natural preservative to reduce S. putrefaciens in fish during cold storage.

Effect of CO2 on the spoilage potential of Shewanella putrefaciens target to flavour compounds

To investigate the regulation mechanism of CO₂ (0% CO₂, 20% CO₂, 60% CO₂, and 100% CO₂) on the spoilage potential of S. putrefaciens target to flavour compounds, the metabolic activity of S. putrefaciens and the changes in flavour compounds extracted from inoculated large yellow croakers were evaluated. Results showed that CO₂ significantly reduced biofilm formation capacity and suppressed synthesis of intracellular adenosine triphosphate (ATP). The production of unpleasant flavour compounds, such as total volatile basic nitrogen (TVB-N), trimethylamine (TMA), inosine (HxR), hypoxanthine (Hx), histidine, lysine, histamine, putrescine, 1-octen-3-ol, hexanal and benzaldehyde, was inhibited by CO₂. The hydrolysis and oxidation of lipid in CO₂-treated samples were alleviated and unsaturated fatty acids (UFAs) were in a higher percentage. In summary, CO₂ efficiently reduced the spoilage potential of S. putrefaciens and contributed to better flavour quality of samples during 4 °C storage. A more effective inhibition by 100% CO₂ was observed.

Effects of chitosan and apple polyphenol coating on quality and microbial composition of large yellow croaker (Pseudosciaena crocea) during ice storage

BACKGROUND

Large yellow croaker (Pseudosciaena crocea) has important commercial value because of its high nutritional value and delicious taste. However, large yellow croaker is readily affected by microorganisms during storage, which causes the corruption of muscle tissue. Both chitosan (CS) and apple polyphenols (APs) are bio-preservatives, which can effectively inhibit the growth of microorganisms and improve the quality of large yellow croaker. The effects of 10.0 and 20.0 g L^-1 CS combined with 1.0 g L^-1 AP coating on the quality and microbial composition of large yellow croaker during ice storage were investigated respectively.

RESULTS

CS + AP coating restrained the increase of total volatile basic nitrogen (TVB-N) and biogenic amines, slowed down the rise of K-value and retarded the growth of microorganisms. The bacteriostatic effect was positively correlated with the concentration of CS. Through the analysis of high-throughput sequencing (HTS), the microbial diversity was changed respectively. The proportion of Shewanella was significantly decreased by CS + AP coating treatment and Pseudomonas was the dominant microorganism in spoiled samples. Compared with the shelf-life of the control group (8 days), 20.0 g L^-1 CS combined with 1.0 g L^-1 AP coating treatment could extend the shelf-life of large yellow croaker for another 8 days.

CONCLUSIONS

CS combined with AP coating may be considered a promising method to delay the biochemical changes of ice stored large yellow croaker and extend its shelf life. © 2021 Society of Chemical Industry.

Effect of Gum Tragacanth-Sodium Alginate Active Coatings Incorporated With Epigallocatechin Gallate and Lysozyme on the Quality of Large Yellow Croaker at Superchilling Condition

This research was done to investigate the synergistic interactions of the gum tragacanth (GT)–sodium alginate (SA) active coatings, incorporated with epigallocatechin gallate and lysozyme, on the quality of large yellow croaker (Larimichthys crocea) during superchilling storage at −3°C. Results showed that the GT-SA active coatings, containing epigallocatechin gallate [EGCG (E), 0.32% w/v], and lysozyme [LYS (L), 0.32% w/v] have reduced the total viable count, psychrophilic bacteria, and Pseudomonas spp. by about 1.55 log CFU/g, 0.49 log CFU/g, and 1.64 log CFU/g compared to the control at day 35. The GT-SA active coatings containing EGCG and LYS were effective in lowering the formations of off-odor compounds such as total volatile basic nitrogen (TVB-N), malondialdehyde (MDA), and off-favor amino acid (histidine). The solid phase microextraction gas chromatography-mass spectrometer (SPME-GC/MS) was applied to characterize and to quantify the volatile compounds of large yellow croaker samples during superchilling storage, while the relative content of the fishy flavor compounds (including 1-octen-3-ol and acetoin) was significantly reduced in the active coatings treated samples. Furthermore, the GT-SA active coatings containing EGCG and LYS treatments was found to be more effective in retarding the migration of water based on magnetic resonance imaging (MRI) results and in maintaining the organoleptic quality of large yellow croaker in superchilling storage at −3°C according to the sensory evaluation results. The results showed that the GT-SA active coating containing EGCG and LYS was effective to be used as a fish preservative to improve the quality and to prolong the shelf life of large yellow croaker in a superchilling storage for at least 7 days.

Effect of multi-frequency ultrasound assisted thawing on the quality of large yellow croaker (Larimichthys crocea)

The effects of mono-, dual- and tri-frequency ultrasound-assisted thawing (UAT) on the physicochemical quality, water-holding capacity, moisture migration and distribution and myofibrillary structure of frozen large yellow croaker (Larimichthys crocea) were detected. The results indicated that multifrequency UAT treatment significantly increased the thawing rate, maintained the stability of myofibrils and reduced the lipid oxidation. The multifrequency UAT samples had better water-holding capacity (higher water-holding capacity values, lower thawing loss and cooking loss) and physicochemical quality (higher hardness, springiness, resilience, chewiness and lower total volatile basic nitrogen (TVB-N) values, thiobarbituric acid reactive substances (TBARS) values), higher immobilized water content, and lower free water content. Therefore, the results provide a further understanding of the quality stability of frozen large yellow croaker treated by the multifrequency UAT.

Effect of Locust Bean Gum-Sodium Alginate Coatings Combined with High CO2 Modified Atmosphere Packaging on the Quality of Turbot (Scophthalmus maximus) during Refrigerated Storage

This research was conducted to investigate the effect of active coatings composed of locust bean gum (LBG) and sodium alginate (SA) containing daphnetin emulsions (DEs) combined with modified atmosphere packaging (MAP) on the microbiological and physicochemical properties of turbot during 4 °C refrigerated storage for 32 days. The results revealed that LBG-SA-DE coatings together with high CO₂ MAP (60% CO₂/35% N₂/5% O₂) maintained the total viable count (TVC) of H₂S-producing bacteria in 4–6 lg CFU/g, which is lower than the limit (7 lg CFU/g). In addition, LBG-SA-DE coatings together with high CO₂ MAP (60% CO₂/35% N2/5% O₂) inhibited the production of odor compounds, including thiobarbituric acid (TBA), trimethylamine-nitrogen (TMA-N), K value, and total volatile basic nitrogen (TVB-N). The low-field NMR analysis (LF-NMR) and magnetic resonance imaging (MRI) indicated that LBG-SA-DE coatings together with high CO₂ MAP (60% CO₂/35% N₂/5% O₂) treatments could delay the release of water located in muscle fiber macromolecules or convert it into free water based on muscle fiber destruction, thus maintaining the water content and migration. The results of the sensory evaluation showed that turbot treated with LBG-SA-DE coatings together with MAP could maintain its freshness during refrigerated storage.

Effect of ultrasonic thawing on the physicochemical properties, freshness, and protein-related properties of frozen large yellow croaker (Pseudosciaena crocea)

Ultrasonic treatment (UT) was used to thaw large yellow croaker in this study, and the effect of various ultrasonic power levels on the quality of large yellow croaker was evaluated after thawing. The effects of ultrasonic on water holding capacity (WHC), moisture distribution, thiobarbituric acid-reactive substance (TBARs), total volatile base nitrogen (TVB-N), ATP degradation (related to K value), surface color change, free amino acid (FAA) content, total sulfhydryl group (SH) content, Fourier transform infrared absorption spectra (FT-IR), fluorescence emission spectra, and microscopic observations of large yellow croaker myofibrillar proteins were investigated. The thawing times of the control sample, 200UT, 240UT, 280UT, and 320UT samples were 1750, 1190, 810, 580, and 570 s, respectively, which indicated that ultrasonic radiation could improve thawing efficiency. Additionally, ultrasonic thawing maintained better freshness and color and inhibited lipid oxidation. Compared with fresh samples, the TVB-N of large yellow croaker thawed by ultrasonication increased by 12.68%, and the K value increased by 0.9%. The 240UT sample had tightly arranged myofibrils and fewer changes in the structures of myogenic fibrillar proteins than the fresh samples, and the SH content of 240UT was decreased by 8.17%. Use of excessive ultrasonic power (320 W) damaged the protein microstructure and the microstructure of large yellow croaker. In conclusion, sample 240UT maintained the quality of large yellow croaker better with minimal damage, which is recommended for rapid thawing. PRACTICAL APPLICATION: Ultrasonic waves improve the thawing efficiency of large yellow croaker and maintain the freshness and color of the fish. According to results, sample 240UT exhibited slight changes in the structure of the myofibril protein, but excessive ultrasonic power destroyed the microstructure and protein structure. Appropriate ultrasonic treatment to the thawing of fish has good prospects.

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

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

Shelf-Life Extension of Large Yellow Croaker (Larimichthys crocea) Using Active Coatings Containing Lemon Verbena (Lippa citriodora Kunth.) Essential Oil

Active coating could improve the fish quality and extend the shelf life. This study investigates the effect of locust bean gum (LBG) and sodium alginate (SA) active coatings containing lemon verbena (Lippa citriodora Kunth.) essential oil (LVEO) emulsions on microbiological, physicochemical and organoleptic evaluation of large yellow croaker (Larimichthys crocea) samples during refrigerated storage at 4°C. Results showed that LBG-SA coatings incorporated with 0.30 or 0.60% LVEO emulsions significantly inhibited the growth of mesophile bacteria, Pseudomonas spp., H₂S-producing bacteria, lactic acid bacteria (LAB) and psychrophilic bacteria, and reduce the productions of trimethylamine (TMA), total volatile basic nitrogen (TVB-N) and ATP-related compounds. Further, the LVEO treatments also retarded the water migration and maintained the organoleptic evaluation results of large yellow croaker during storage at 4°C. In conclusion, the LBG-SA active coatings incorporated with LVEO emulsions maintained the quality and extended the shelf life of large yellow croaker during refrigerated storage.

Effect of locust bean gum-sodium alginate coatings incorporated with daphnetin emulsions on the quality of Scophthalmus maximus at refrigerated condition

In this study, the microbiological, physicochemical, and flavor changes of turbot (Scophthalmus maximus) coated with a composite active coating of locust bean gum (LBG) and sodium alginate (SA) supplemented with daphnetin emulsions (0.16, 0.32, 0.64 mg·mL^-1) were determined during 18 days of refrigerated storage (4 ± 1 °C). Results showed that LBG-SA coatings containing 0.32 mg·mL^-1 daphnetin emulsions could significantly lower the total viable count (TVC), psychrophiles, Pseudomonas spp. and H₂S-producing bacteria counts, and inhibit the productions of off-flavor compounds including the total volatile basic nitrogen (TVB-N), trimethylamine (TMA) and ATP-related compounds. 32 volatile compounds were identified by solid phase microextraction combined with gas chromatography-mass spectrometer method (SPME-GC/MS) during refrigerated storage and the treated turbot samples significantly lowered the relative content of fishy flavor compounds. Further, the LBG-SA coatings containing daphnetin could also delay the myofibril degradation of the turbot samples. These results indicated that the LBG-SA coatings with 0.32 mg·mL^-1 daphnetin were a potential alternative way to improve the quality of turbot during refrigerated storage.

Use of Spectroscopic Techniques to Monitor Changes in Food Quality during Application of Natural Preservatives: A Review

Consumer demand for food of high quality has driven research for alternative methods of food preservation on the one hand, and the development of new and rapid quality assessment techniques on the other hand. Recently, there has been a growing need and interest in healthier food products, which has led to an increased interest in natural preservatives, such as essential oils, plant extracts, and edible films and coatings. Several studies have shown the potential of using biopreservation, natural antimicrobials, and antioxidant agents in place of other processing and preservation techniques (e.g., thermal and non-thermal treatments, freezing, or synthetic chemicals). Changes in food quality induced by the application of natural preservatives have been commonly evaluated using a range of traditional methods, including microbiology, sensory, and physicochemical measurements. Several spectroscopic techniques have been proposed as promising alternatives to the traditional time-consuming and destructive methods. This review will provide an overview of recent studies and highlight the potential of spectroscopic techniques to evaluate quality changes in food products following the application of natural preservatives.