TCA-soluble Peptides Research Articles

Independent and combined effects of ultrasound and transglutaminase on the gel properties and in vitro digestion characteristics of bay scallop (Argopecten irradians) adductormuscle

The effects of transglutaminase (TGase) addition (0.4–1.2 g/100g), ultrasound (120–720 W, 20 min), and their combination on the gel properties and in vitro digestion characteristics of bay scallop adductor muscle were studied. The gel strength of the gel sample with TGase content of 0.8 g/100g (TG-0.8) was 58.2% higher than that of the control sample (CON). The gel sample treated with ultrasound at 480 W (UT-480) had the highest gel strength. The strength of the gel prepared by combination of 0.8 g/100g TGase and 360 W ultrasound (UT-TG) was 82.3% higher than that of CON. The whiteness and water holding capacity of the gel increased regardless of the addition of TGase or ultrasound treatment. SDS-PAGE patterns showed that the myosin heavy chain of the treated samples became thinner, and the changes of actin and tropomyosin were not significant. The scanning electron microscopy results of gel samples prepared by ultrasound combined with TGase showed a denser structure, which was related to the lowest total sulfhydryl content and TCA-soluble peptide content. The results of dynamic rheology show that the UT-TG sample had the highest G′ value, followed by TG-0.8. The in vitro digestion characteristics of the selected gel samples were also discussed. The degree of protein hydrolysis and the content of free amino acids in TG-0.8 samples were the lowest, which improved after ultrasound treatment. Overall, the combination of appropriate ultrasound treatment and TGase addition provides an effective means for improving gel properties and digestibility of scallop surimi product.

Assessment of spoilage potential and amino acids deamination & decarboxylation activities of Shewanella putrefaciens in bigeye tuna (Thunnus obesus)

Two Shewanella putrefaciens strains (00A and 00B) were inoculated into sterile bigeye tuna blocks. The biochemical changes (trichloroacetic acid (TCA)-soluble peptides, total volatile basic nitrogen (TVB-N), ammonia, trimethylamine (TMA), biogenic amines (BAs), free amino acids (FAA), and total amino acids (TAA)), decarboxylation and deamination activities of S. putrefaciens in bigeye tuna blocks were investigated in this study. All indicators, except for histamine, showed that 00A had a stronger spoilage potential than 00B. The extremely low histamine decarboxylation activities of 00A and 00B may be the main reason for the non-significant difference (p > 0.05) between the two groups in tuna. Meanwhile, arginine deiminase pathway can produce large amounts of putrescine and energy, and arginine deiminase may be the main rate-limiting enzyme of the whole pathway. Principal component analysis (PCA) revealed that the difference between TCA-soluble peptide and FAA content in the inoculated groups may be the main reason for the difference in the spoilage potential of the two strains.

Reduced Washing Cycle for Sustainable Mackerel (Rastrelliger kanagurta) Surimi Production: Evaluation of Bio-Physico-Chemical, Rheological, and Gel-Forming Properties.

Although dark muscle is currently the most important obstacle in marketing high-quality Indian mackerel (Rastrelliger kanagurta) surimi, reducing washing remains a challenge for long-term surimi production from this species. Herein, the impact of washing cycles (one (W1), two (W2), and three (W3) cycles) with a 1:3 mince to water ratio on the bio-physico-chemical properties, rheology, and gelling ability of mackerel surimi was evaluated. The yield, Ca2+-ATPase activity, TCA-soluble peptide, and myoglobin contents of surimi decreased as the number of washing cycles increased, while lipid removal, reactive SH content, and surface hydrophobicity of surimi increased. Surimi generated by W2 and W3 provided the same rheological patterns and Fourier-transform infrared spectroscopy (FTIR) spectra as unwashed mince, with the highest gel strength and whiteness, as well as the lowest expressible drip, thiobarbituric acid reactive substances (TBARS), and fishy odor. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) demonstrated the presence of polymerized proteins stabilized by disulfide and other interactions. Using a scanning electron microscope, several concentrated dense areas and distributed pores generated by myofibrillar proteins gel networks were found. Surimi from W2 and W3 appeared to be of similar overall quality, however W2 had a larger yield. As a result of the evaluation of bio-physico-chemical, rheological, and gel-forming capabilities, as well as product yield, W2 may be the best option for producing high-quality surimi from Indian mackerel in a sustainable manner.

Improving the quality characteristics of rice mash grass carp using different microbial inoculation strategies

The effects of different microbial inoculation strategies on the quality of Chinese traditional rice mash grass carp were investigated. Individual inoculation (Pediococcus pentosaceus 220, Staphylococcus xylosus 135, Saccharomyces cerevisiae 22), and mixed triple inoculation of the above strains (Pediococcus-Staphylococcus-Saccharomyces, PSS) were employed, including an uninoculated control. It was found that the inoculated microbes proliferated differently, depending on the inoculation regime. The decreases of pH, hardness, and increases of TCA-soluble peptides were accelerated, while the accumulation of TVB-N and TBARS was reduced in all inoculated groups. A significantly higher level of total free amino acids was found in PSS-inoculated grass carp (P < 0.05), as well as alcohols and esters. Moreover, the total sensory score of PSS-inoculated grass carp with 15-day fermentation was closest to the control with 30-day fermentation. Consequently, the inoculation of a mixed starter culture could help reduce the fermentation time of rice mash fish by 50% while providing the optimum texture and flavor.

Effect of ultrasound pre-treatment modes on gelation properties of silver carp surimi

The aim of this study was to illustrate the effect of high intensity ultrasound (HIU) pre-treatment modes (HIU pre-treatment before salt-chopping (HIUBC), after salt-chopping (HIUAC) and after stuffing into polyvinylidene chloride casing (HIUAS)) on the gelation properties of silver carp surimi. HIUBC facilitated the protein dispersion and more compact microstructures formation, which was beneficial to obtaining the highest water-holding capacity (WHC) of HIUBC gels. Meanwhile, the puncture properties of HIUBC gels were significantly improved via the formation of more ε-(γ-Glu)-Lys and S–S bonds. HIUAC and HIUAS promoted the formation of ε-(γ-Glu)-Lys bonds, but also induced the protein degradation, as evidenced by the decreased solubility and relatively higher TCA-soluble peptides. Thus, no obvious improvement of puncture properties and WHC was observed for HIUAC or HIUAS gels. In conclusion, HIUBC was beneficial to facilitating protein dispersion, thereby improving gelation properties of surimi during heat-induced gelling process. However, HIUAC and HIUAS hardly influenced gelation properties of surimi. This might provide an effective method of HIU pre-treatment for promoting gelation properties of surimi.

Comparative quality and volatilomic characterisation of unwashed mince, surimi, and pH-shift-processed protein isolates from farm-raised hybrid catfish (Clarias macrocephalus × Clarias gariepinus)

Earthy off-odour in farm-raised freshwater fish is considered a quality defect. This study aimed to investigate the potential of pH-shift processing to remove off-odours from farm-raised hybrid catfish while at the same time documenting de-novo formation of other volatile compounds. In comparison with crude mince and conventional surimi, the alkali pH-shift process gave larger reductions in geosmin, 2-methylisoborneol, undesirable volatile compounds (e.g. hexanal, (E)-2-nonenal, (E)-2-heptenal, 2-butanone, and hexadecane), lipids, myoglobin, total volatile basic nitrogen, and TCA-soluble peptides (p < 0.05). The acid-produced protein isolate showed the highest TBARS and processing-induced evolution of the following volatiles: octanal, nonanal, decanal, 2-butyl-2-octenal, pentadecanal, 1-hexanol, 1-octanol, 1-octen-3-ol, and 2,3-octanediol (p < 0.05). Alkali-aided process provided better overall gelling characteristics (i.e. breaking force, deformation, and texture profile) and gave lower fishy, earthy, and rancid off-odour scores (p < 0.05). Thus, alkali pH-shift process can be used to isolate gel-forming proteins from hybrid catfish while minimizing the accumulation of undesirable volatile compounds.

Physicochemical characteristics and textural parameters of restructured pork steaks hydrolysed with bromelain

Enzymatic tenderisation including bromelain enhances underused cuts of meat in emerged restructuring technology. Physicochemical and textural characteristics of restructured pork steak hydrolysed with bromelain for masticatory dysfunction people were evaluated. Restructured pork steak treated with bromelain at 0.05 and 0.1% (w/w) was hydrolysed at 50 °C for 0, 3, 6, 9 and 12 min. The cooking losses of 0.05% (w/w) bromelain for 0, 3 and 6 min were lower than 0.1% (w/w) bromelain samples. The ΔE increased after increasing the enzyme concentration and hydrolysis time. Bromelain-treated samples at higher concentrations showed lower WBSF, KSF and TPA parameters, but cohesiveness of 0.05% (w/w) had higher than 0.1% (w/w) bromelain samples. Total protein, sarcoplasmic protein solubility, TCA-soluble peptide, total collagen and soluble collagen contents were the highest in 0.1% (w/w) bromelain-treated samples for 12 min (P < 0.05). According to SDS-PAGE and SEM, various proteins in the enzyme-treated samples were degraded.

Changes in taste substances during fermentation of fish sauce and the correlation with protease activity

Anchovy sauce shows different taste profiles under different fermentation time. The change rules of free amino acids was measured by amino acid analyzer, and other taste substances, such as nucleotides and organic acids in anchovy sauce under different fermentation time were also investigated. Moreover, the correlation between protease activity and taste substances in anchovy sauce fermentation was analyzed by orthogonal partial least squares. Throughout the fermentation process, the taste substances in anchovy sauce increased during early months and then decreased as time increased. The content of amino acid nitrogen, TCA-soluble peptides, 5′-nucleotides (AMP, GMP, IMP) and organic acids (lactic acid, succinic acid) in anchovy sauce increased by 26%, 33%, (45%, 35%, 68%) and (27%, 2%) respectively in comparison with 6 months fermentation. Total amino acid content reached its maximum after 18 months fermentation. Results of electronic tongue demonstrated that the umami of anchovy sauce after 12 months fermentation increased by 17% in comparison with 6 months fermentation. A model correlating changes in protease activity with taste formation suggested that protease activity impacted the content of Ala, Glu, Lys, Asp, Leu, TCA-soluble peptides and succinic acid. This study can provide empirical evidence to guide the efficient processing of anchovy sauce.

Physicochemical characteristics and flavor profiles of fermented fish sauce (budu) during fermentation in commercial manufacturing plant.

This study was done by dynamically monitoring the changes in bacterial composition, physicochemical characteristics, and volatile substances during fermentation of fermented fish sauce (budu). The degree of hydrolysis, TCA-soluble peptides, and nitrogen contents increased as the fermentation time progressed. A continuous decrease in peroxide value and thiobarbituric acid reactive substances was noted over 60days of fermentation. A total of 44 volatile compounds were detected, and increases in volatile compounds, such as 2-methylbutanal, 3-methylbutanal, benzaldehyde, and 2-ethyl furan, with low odor thresholds values, might contribute to budu's flavor of the final product. Additionally, the relationship between evolving microbiota and the formation of flavor compounds was analyzed, and halophilic lactic acid bacteria was identified to be the most important bacterial contributing to flavor and aroma development. This finding will provide important information for improving thequality of budu in terms of flavor characteristics.

Autolysis of Pacific white shrimp (Litopenaeus vannamei) processing by-products: Enzymatic activities, lipid and protein oxidation, and antioxidant activity of hydrolysates

Autolysis (at fixed temperatures (FT) or gradually increasing temperatures (GIT) with different times) was studied by measuring enzymatic activities, lipid and protein oxidation, and antioxidant activity of Pacific white shrimp by-product hydrolysates. Trypsin had its highest activity at 40 °C, 2 h and pH 8 (45 mU/mL) followed by 40 °C, 3 h and pH 8 (40 mU/mL) (P ≤ 0.05). The increase in autolysis time and temperature was accompanied by a drop-in enzyme activity and TCA-soluble peptide content (P ≤ 0.05). The peptide fraction with MW < 1000 Da was the main peptide fraction, accounting for 97.0, 98.4, and 96.7% of total peptides in FT-40 (1 h), FT-60 (3 h) and GIT (3 h), respectively. The order of lipid oxidation was FT-60 > GIT > FT-50 > FT-40. FT-50 and FT-60 had the lowest sulfhydryl group content with a coincidental higher protein carbonyl (P ≤ 0.05). The higher temperatures of FT led to a decrease of essential amino acids, especially when autolysis time increased. GIT showed the highest DPPH radical scavenging activity, ferric reducing antioxidant power (FRAP) and metal chelating ability (P ≤ 0.05). Results might be useful to increase the value of Pacific white shrimp by-products for protein hydrolysates production using autolytic hydrolysis technology.

Autolysis of rainbow trout (Oncorhynchus mykiss) by-products: Enzymatic activities, lipid and protein oxidation, and antioxidant activity of protein hydrolysates

Autolysis (at fixed temperatures (40, 50, 60 °C) or gradually increasing temperatures (40-60 °C) with different times) was used to produce protein hydrolysates from rainbow trout processing by-products. Total proteolytic and trypsin activities with fixed temperatures was higher than gradually increasing temperatures, decreased with increasing autolysis time and temperature with fixed temperatures (P ≤ 0.05). TCA-soluble peptides decreased with increasing autolysis times from 1 to 3 h (P ≤ 0.05). Autolysis increased peroxide value and thiobarbituric acid-reactive substances in both lipids and hydrolysates, particularly with gradually increasing temperatures (P ≤ 0.05) and was associated with oxidation of polyunsaturated fatty acids. Sulfhydryl groups decreased, while protein carbonyls and solubility were increased with fixed temperatures at higher temperatures (50 and 60 °C) or with gradually increasing temperatures at longer autolysis time (P ≤ 0.05). Free radical scavenging activity and the metal chelating ability of hydrolysates were governed by autolysis times and temperatures. Results of size exclusion chromatography-high performance liquid chromatography indicated that autolysis for 1 h at lower temperature (40 °C) was sufficient to produce autolysates rich in small peptides from rainbow trout by-products. Autolytic hydrolysis might be useful for production of such protein hydrolysates.

Effect of high intensity ultrasound on gelation properties of silver carp surimi with different salt contents

Surimi from silver carp with different salt contents (0–5%) was obtained treated by high intensity ultrasound (HIU, 100 kHz 91 W·cm−2). The gelation properties of samples were evaluated by puncture properties, microstructures, water-holding capacity, dynamic rheological properties and intermolecular interactions. As the salt content increased from 0 to 5%, gel properties of surimi without HIU significantly improved. For samples with low-salt (0–2% NaCl) content, HIU induced obvious enhancement in breaking force and deformation. HIU promoted the protein aggregation linked by SS bonds, hydrophobic interactions and non-disulfide covalent bonds in surimi gels with low-salt content. Moreover, microstructures of HIU surimi gels with low-salt content were more compact than those of the corresponding control samples. HIU also improved the gelation properties of surimi with 3% NaCl to an extent. However, for high-salt (4–5% NaCl) samples, HIU decreased the breaking force and deformation of surimi gels due to the degradation of proteins suggested by increased TCA-soluble peptides. In conclusion, HIU effectively improved the gelation properties of surimi with low-salt content (0–2% NaCl), but was harmful for high-salt (4–5% NaCl) surimi. This might provide the theoretical basis for the production of low-salt surimi gels.

Effect of protein oxidation and degradation on texture deterioration of ready-to-eat shrimps during storage.

The impact of protein oxidation and degradation on texture deterioration of ready-to-eat (RTE) shrimps during storage was investigated. The deterioration in texture during storage was manifested by decreased instrumental hardness, elasticity, chewiness, and recoverability. The occurrence of protein oxidation was revealed by a significant increase in the contents of free radicals and carbonyls. The increases in trichloroacetic acid-soluble peptide (TCA-soluble peptide) content and myofibril fragmentation index (MFI) were also observed, suggesting the degradation of protein. Pearson correlation analysis showed that the decreased instrumental texture parameters were negatively correlated with the increased carbonyl content, TCA-soluble peptide, MFI, porosity, and pore size as well as the decreased water-holding capacity (WHC), thus, it was hypothesized that protein oxidation and degradation were responsible for changes in the microstructure and reduction of WHC, which ultimately resulted in texture deterioration of RTE shrimps.

Microbial succession and the changes of flavor and aroma in Chouguiyu, a traditional Chinese fermented fish

Chouguiyu (stinky Mandarin fish), a traditional spontaneously fermented fish in China, is famous for its unique aroma and pleasant taste. However, the relationships between the succession of microorganisms during the fermentation and the formation of Chouguiyu's unique aroma and taste remain to be characterized. In this study, 16S rRNA gene amplicon sequencing was done to investigate the evolving microbiota during Chouguiyu fermentation, and the volatile compounds and amino acids profiles were measured alongside with chemical characterization of the samples (e.g., determination of pH, TVB-N, TBARS, and TCA-soluble peptides). Based on the changes of the microbiota, the fermentation was categorized into two stages: early-fermentation, 1st-3rd days; and late-fermentation, 4th-7th days. Linalool, piperitone, anethole, 1-octen-3-ol, 2-methyl-3-octanone and indole were identified as characteristic volatile compounds in Chouguiyu. According to the sensory evaluation results, the flavor of the Chouguiyu was reinforced in the late-fermentation stage. Redundancy analysis showed the relationships between evolving microbiota and the formation of Chouguiyu's aroma and taste, and Psychrilyobacter was identified to be the most important bacterial genus contributing to flavor and aroma development, followed by Fusobacterium, Arcobacter and Oceanisphaera. These genera were positively correlated with Glu, Met, Tyr, Pro, linalool, piperitone, indole, TBARS, TVB-N, and TCA, and influenced the flavor and aroma of the Chouguiyu. The results of this study provided a scientific basis to further improve Chouguiyu production.

Impact of pilot-scale processing (thermal, PEF, HPP) on the stability and bioaccessibility of polyphenols and proteins in mixed protein- and polyphenol-rich juice systems

Due to health-beneficial effects of polyphenols, their stability and bioaccessibility in strawberry puree as influenced by processing (thermal, pulsed electric field (PEF), high pressure processing (HPP)) and by combination with relatively protein-rich vegetable juice (kale) was investigated.Soluble strawberry anthocyanins decreased in the presence of kale, in a processing-dependent manner, likely due to interactions with kale proteins. In the strawberry-water-system, polyphenols increased after processing due to increased extraction, especially after thermal and PEF, while in the mix anthocyanins increased especially after HPP and PEF. Anthocyanin structure affected the ratio of free anthocyanins after the interaction. During gastric digestion, an increase in bioaccessible anthocyanins was observed, while during intestinal digestion it strongly diminished. Thermal, PEF and formulation of the mix reduced soluble protein fractions, as observed by decreasing SDS-PAGE band intensity. The proteins were easily digestible and after 15 min of gastric digestion, no bands appeared with an increase in TCA soluble peptides. Industrial relevanceWith the increase in health awareness and the changing on-the-go lifestyle, consumers demand convenient fruit and vegetable-based products with high nutritional and health-promoting content. Thus, utilization of alternative processing with minimal impact on the quality of fruit and vegetable juices is considered as a promising tool to deliver such high nutritional products, however, little is known about their effect on multi-component juice systems, where interactions between the different components can occur. Strawberries are the most commonly consumed berry type, delivering high quantities of polyphenols and therefore a representative polyphenol-rich model system. Kale is gaining increasing attention due to the nutritional profile, above others, it contains relatively (to other fruits and vegetables) high protein content, and therefore displays an interesting vegetable-based protein-rich model. A more in-depth understanding of the effect of alternative processing on polyphenol-protein interactions in these increasingly popular mixed systems (green smoothies) and the digestive fate of these potentially health-beneficial compounds is studied and provides new insights into designing functional products attractive for consumers.

Combined effect of microbial transglutaminase and ethanolic coconut husk extract on the gel properties and in-vitro digestibility of spotted golden goatfish (Parupeneus heptacanthus) surimi gel

The combined effects of microbial transglutaminase (MTGase) and ethanolic coconut husk extracts (ECHE) at various concentrations on gelling properties of spotted golden goatfish (SGG) (Parupeneus heptacanthus) surimi were investigated. When gel was added with MTGase at various levels (0.5–2 U/g paste), the gel containing 1 U/g paste (MT-1) had the highest increase (284%) in breaking force (BF), compared to that of the control gel (CON). Similarly, with ECHE incorporation (0.05–0.25%, based on protein content), BF was increased to the maximum value with the addition of 0.1% ECHE (EC-0.1), in which BF was augmented by 59% than the CON. When MT-1 sample was incorporated with 0.15% ECHE (MT-EC), BF was increased by 709% as compared to that of CON. Gel added with ECHE alone had lower whiteness than the CON (p<0.05). However, MTGase increased the whiteness of all gel samples, regardless of ECHE addition. MT-EC samples had higher water holding capacity than the CON (p<0.05). Electrophoretic studies showed the disappearance of myosin heavy chain (MHC) bands with the incorporation of both additives at all levels used. MT-EC sample showed the highest Gʹ value, followed by MT-1. Impact of in-vitro digestion on antioxidant activity of selected SGG surimi gels was also elucidated. During in-vitro digestion, the MT-EC and MT-1 samples had the lowest TCA-soluble peptide content. The highest antioxidant activity was obtained for MT-EC and EC-0.1 samples (p<0.05). Hence, the combination of MTGase and ECHE at appropriate levels could yield a gel with improved gelling properties and enhanced antioxidant potential after the in-vitro digestion.

Effects of ethyl lauroyl arginate hydrochloride on microbiota, quality and biochemical changes of container-cultured largemouth bass (Micropterus salmonides) fillets during storage at 4 °C

This study aimed to investigate preservative effects of ethyl lauroyl arginate hydrochloride (LAE) on microbiota, quality, and physiochemical changes of container-cultured largemouth bass fillets stored at 4 °C. The results showed LAE treatment was effective in reducing bacterial growth and attenuating physiochemical changes (flesh color, trichloroacetic acid (TCA)-soluble peptides, total volatile basic nitrogen (TVB-N), ammonia concentration, and biogenic amines) of bass fillets, while had relatively weak effect on the degradation of ATP-related compounds. As a result, LAE treatment retarded the deterioration of sensory attributes, and thus prolonged the shelf-life of largemouth bass fillets for 4 days. In addition, LAE treatment decreased the relative abundance of Pseudomonas in bass fillets, and thus changed the microbial composition. Moreover, correlation analysis between physiochemical changes and bacterial genera showed that Pseudomonas was well correlated with TCA-soluble peptides, TVB-N, ammonia, putrescine and histamine, while Aeromonas tended to have strong potentials in producing ammonia and cadaverine.

Proteome analysis reveals the important roles of protease during tenderization of sea cucumber Apostichopus japonicus using iTRAQ.

The tenderization mechanism in sea cucumber Apostichopus japonicus was investigated. Effects of three kinds of protease inhibitors on proteolysis in the tenderized Apostichopus japonicus body wall (AJBW) were characterized. The protein profiles in AJBW were determined at 0 h (CON), 1 h (T_1h), 3 h (T_3h) and 12 h (T_12h) after tenderization by isobaric tags for relative and absolute analysis quantitation. Results indicated inhibitors of cysteine, serine protease and matrix metalloproteinase (MMP) could prevent the release of TCA-soluble peptides and hydroxyproline. Proteomic analysis revealed 1865, 857 and 1587 differential abundant proteins at T_1h, T_3h and T_12h, respectively. The expressions of key proteins including cathepsins, calpains, caspases, proteasomes and MMPs were upregulated. Furthermore, proteins involved in oxidative stress response, innate immune response, apoptosis and reorganization of cytoskeleton and extracellular matrix were upregulated, which could be the potential biomarkers. Our findings revealed important mechanism of tenderization in AJBW which will lead to better understanding of this important process.

Biochemical changes induced by dominant bacteria in chill-stored silver carp (Hypophthalmichthys molitrix) and GC-IMS identification of volatile organic compounds

To evaluate the spoilage potential of dominant bacteria (Aeromonas allosaccharophila, Pseudomonas psychrophila, and Shewanella putrefaciens) isolated from spoiled silver carp (Hypophthalmichthys molitrix) fillets, biochemical changes including protein degradation, trichloroacetic acid (TCA)-soluble peptides, total volatile basic nitrogen (TVB-N), biogenic amines, nucleotide catabolism, and volatile organic compounds were examined in single-species inoculated silver carp flesh for 14 days at 4 °C. P. psychrophila exhibited the strongest proteolytic activity, which resulted in the highest concentrations of TCA-soluble peptides and TVB-N. S. putrefaciens was responsible for the production of putrescine and cadaverine and led to the fastest degradation of hypoxanthine riboside (HxR). At the end of storage, P. psychrophila was the main producer of ketones, especially the C7-C9 ketones, while sulfur compounds were released primarily by S. putrefaciens. Moreover, 1-propanol, butanone, 2-hexanone, methyl isobutyl ketone, dimethyl sulfide, and dimethyl disulfide increased gradually with storage time, suggesting their potential as spoilage markers for freshness/spoilage monitoring. P. psychrophila possessed the strongest spoilage potential in the fish matrix, followed by S. putrefaciens, whereas A. allosaccharophila showed a very low spoilage potential. In conclusion, P. psychrophila and S. putrefaciens were identified as the specific spoilage organisms (SSOs) of silver carp, suggesting that preservation researchers should focus on these two spoilage contributors in future studies. This research contributes to a deeper understanding of silver carp spoilage and to the development of methods and tools to improve fish quality management.

Evaluation of water dynamics and protein changes in bigeye tuna (Thunnus obesus) during cold storage

The objective of this study was to investigate water dynamics and protein changes in bigeye tuna (Thunnus obesus) stored at 0 °C and 4 °C for up to 6 days. The values of various protein parameters (trichloroacetic acid (TCA)-soluble peptide content, Ca2+-ATPase enzyme activity and total -SH content) decreased with increasing storage time. Fourier transform infrared spectra indicated that the secondary structure of the proteins changed; the contents of α-helixes and β-turns significantly decreased, while that of β-sheets significantly increased (p < 0.05). Atomic force microscopy and sodium dodecyl sulfate-polyacrylamide gel electrophoresis results revealed that the length, diameter and height of the myofibril proteins decreased significantly and that myosin and actin degraded during cold storage. The results of low-field nuclear magnetic resonance (LF-NMR) spectroscopy showed that T21 (trapped water) was positively correlated (p < 0.01) with water-holding capacity (WHC), Ca2+-ATPase activity, and the total contents of -SH groups, ionic bonds, hydrogen bonds, α-helixes and random coils. In addition, T21 was negatively correlated (p < 0.01) with the contents of TCA-soluble peptides, hydrophobic interactions, disulfide bonds and β-sheets. Therefore, the correlation between water dynamics and protein changes was successfully shown and can be used to monitor changes in the quality of bigeye tuna during cold storage.