Exploring the correlation of microbial community diversity and succession with protein degradation and impact on the production of volatile compounds during cold storage of grouper (Epinephelus coioides).

Microorganisms, proteins, and lipids play crucial and intricate roles in the aroma generation of aquatic products. To explore the impact of the interaction between microorganisms and proteins on the volatile compounds (VOCs) in grouper, this study employed whey protein isolate (WPI) to inhibit lipid oxidation and reduce mutual interference. Changes in bacterial profiles, metabolites, and VOCs were detected. Eighteen key VOCs associated with the overall flavor of grouper were identified, and the potential relationships among microorganisms, proteins, and VOCs were explored using a correlation network. Five microorganisms (Vibrio, Vagococcus, Pseudomonas, Psychrobacter, and Shewanella) closely related to characteristic flavor compounds were identified. Additionally, 30 differential metabolites related to proteins and six metabolic pathways were screened. Therefore, this study unveils the potential interaction between microorganisms and proteins in flavor formation and provides new insights into the relationships among microorganisms, proteins, and VOCs.

The application of ice glazing containing D-sodium erythorbate combined with vacuum packaging to maintain the physicochemical quality and sweet/umami non-volatile flavor compounds of frozen stored large yellow croaker (Pseudosciaena crocea).

Ice glazing containing 0.3 % D-sodium erythorbate (DSE), combined with vacuum packaging, was used as a method to maintain the quality of large yellow croaker during frozen storage. This study aimed to assess various aspects, including water properties (water holding capacity and moisture distribution), protein-related characteristics (secondary and tertiary structure of myofibrillar protein), freshness indicators (K value and total volatile base nitrogen (TVB-N)), and non-volatile flavor compounds (free amino acids (FAAs) and nucleotides) in samples stored for 300 days at -23 °C. The results showed that vacuum packaging had a significant inhibitory effect on the growth of ice crystal. Notably, it successfully maintained the cross-sectional area of nearly all ice crystals below 20,000 µm2, effectively curtailing water loss. Simultaneously, the combination of vacuum packaging with the complex ice glaze effectively mitigated the degradation of IMP and free amino acids, maintaining low levels of K value (12.85 %) and TVB-N (11.28 mg N/100 g) throughout the 300-day frozen storage, retaining first-class freshness. Among the various treatment modalities assessed, the combined application of vacuum packaging and 0.3 % DSE-infused ice glazing emerged as the most effective in terms of preservation outcomes. This efficacious combination shows promising potential for the frozen storage of aquatic products and is therefore recommended for practical implementation.

Exploring the effects of lipid oxidation and free fatty acids on the development of volatile compounds in grouper during cold storage based on multivariate analysis.

To investigate the relationship between lipid oxidation and the development of volatile compounds (VOCs) in grouper lipid during cold storage, lipids were extracted from grouper as a single-factor study to avoid the complex interactions between microorganisms and proteins. Lipid oxidation during storage and the content of 12 long-chain fatty acids (FAs) in grouper lipids were evaluated. The HS-SPME-GC-MS technique was used to analyze the VOCs in grouper lipids, and a total of 13 key VOCs, primarily comprising alcohols and aldehydes, were screened. Pearson correlation analysis showed a strong acorrelation between these 13 key VOCs, which influenced the overall flavor of grouper lipids, and lipid oxidation, mainly involving secondary oxidation of lipids and the oxidation of long-chain polyunsaturated fatty acids, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Possible solutions for grouper lipid deterioration were proposed, providing a reference for maintaining the overall quality of grouper and regulating flavor formation.

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.

Factors affecting the quality of frozen large yellow croaker (Pseudosciaena crocea) in cold chain logistics: Retention time and temperature fluctuation.

The purpose of this study is to provide a reference for avoiding the quality loss of large yellow croaker in cold chain transportation. The effects of retention time before freezing and temperature fluctuation caused by transshipment in logistics were evaluated by TVB-N, K value, TMA value, BAs, FAAs content and protein-related characteristics. The results showed that the retention would lead to the rapid increase of TVB-N, K value, and TMA value. And the temperature fluctuation would further lead to deterioration of these indicators. We concluded that the influence of retention time was far greater than that of temperature fluctuation. In addition, the bitter free amino acids (FAAs) were highly correlated with the freshness-related indicators, which could reflect the freshness changes of samples, especially the quantity of histidine. Therefore, it is suggested to freeze samples immediately after catching and try to avoid temperature fluctuations during cold chain to maintain the quality.

Potential of Good's buffers to inhibit denaturation of myofibrillar protein upon freezing.

The current systematic study sought to examine the potential use of three Good's buffers (MES, MOPS and HEPES) in inhibiting myofibrillar protein (MFP) denaturation induced by acidity changes. The highest degree of acidity variation was found in the center and bottom of large bottles due to the freeze-concentration effect. Good's buffer tended to basify during freezing, and it could prevent the crystallization of sodium phosphate (Na-P) buffer. Acidification upon freezing Na-P disrupted the natural conformation of MFP and induced the formation of large proteins aggregates with tight packing. The 15 mM MES, 20 mM MOPS, and 30 mM HEPES were respectively added to neutralize the strong acidity drop induced by freezing 20 mM Na-P, and all of them significantly improved the stability of the MFP conformation (P < 0.05). This work is not only critical to meet the growing demand for protein, but also groundbreaking for broadening the applicability of Good's buffers in the food industry.

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.

Effects of Dual-Frequency Ultrasound-Assisted Thawing Technology on Thawing Rate, Quality Properties, and Microstructure of Large Yellow Croaker (Pseudosciaena crocea).

This research evaluated the effects of dual-frequency ultrasound-assisted thawing (UAT) on the thawing time, physicochemical quality, water-holding capacity (WHC), microstructure, and moisture migration and distribution of large yellow croaker. Water thawing (WT), refrigerated thawing (RT), and UAT (single-frequency: 28 kHz (SUAT-28), single-frequency: 40 kHz (SUAT-40), dual-frequency: 28 kHz and 40 kHz (DUAT-28/40)) were used in the current research. Among them, the DUAT-28/40 treatment had the shortest thawing time, and ultrasound significantly improved the thawing rate. It also retained a better performance from the samples, such as color, texture, water-holding capacity and water distribution, and inhibited disruption of the microstructure. In addition, a quality property analysis showed that the pH, total volatile basic nitrogen (TVB-N), and K value were the most desirable under the DUAT-28/40 treatment, as well as this being best for the flavor of the samples. Therefore, DUAT-28/40 treatment could be a possible thawing method because it improves the thawing rate and maintains the quality properties of large yellow croaker.

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.

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

The present study evaluated the effects of chitosan (CH) and sodium alginate (SA) bioactive coatings containing 0.1, 0.2 and 0.3% ε-polylysine (ε-PL) combined with high CO2 modified atmosphere packaging conditions (MAP, 60% CO2/5% O2/35% N2) on the quality of cultured pufferfish (Takifugu obscurus) at 4 °C for 18 days. Results showed that CH-SA coatings containing ε-PL and high CO2 MAP treatments could significantly lower total viable count (TVC), Pseudomonas spp., H2S-producing bacteria and lactic acid bacteria counts (LAB), and reduce the productions of off-flavor compounds including total volatile basic nitrogen (TVB-N), trimethylamine (TMA) and ATP-related compounds. Volatile compounds were identified and quantified by SPME gas chromatography-mass spectrometer (SPME-GC/MS) for pufferfish during cold storage and the bioactive coating treated pufferfish significantly lowered the relative content of fishy flavor compounds, such as 1-octen-3-ol, hexanal, (E)-2-octenal, octanal and 2,3-butanedione. Further, CH-SA coatings containing ε-PL and high CO2 MAP treatments could more efficiently retard the water migration by magnetic resonance imaging (MRI) results, and maintained the quality of pufferfish during storage at 4 °C according to organoleptic evaluation results.