Changes of the flavor substances and protein degradation of black carp (Mylopharyngodon piceus) pickled products during steaming.

BACKGROUND: Among various cooking methods, steaming is favored by many because it can cause less damage to nutrient components in muscle, retain the inherent food flavor, and reduce the generation of harmful substances. Steaming conditions are closely related to fish flavor, fat and protein oxidation, and digestibility. RESULTS: The black carp steamed for 4 to 14 min was studied in this article based on sensory assessment, electronic tongue, free amino acids, adenosine triphosphate (ATP)-related compounds, total nitrogen and non-protein nitrogen to explore the effect of steaming time on the taste substances and protein degradation of pickled black carp. The experimental result showed that the meat steamed within 8 min tasted better, showing high tastiness. The sensory assessment score increased significantly to the maximum value of 82.33 at 6 min. The content of umami and sweet amino acids increased significantly to the maximum value of 1.6801 g kg-1 at 6 min. In the meantime, the IMP (inosine monophosphate) content was 1.9128 g kg-1 , with its taste activity value (TAV) reaching 7.65, which proved that IMP affected the taste most. Furthermore, the total nitrogen content was 30.77 g kg-1 , which meant protein degraded a great deal. Based on equivalent umami concentration (EUC) and its TAV, the meat tasted best at 6-8 min. The longer the steaming time, the faster the protein degradation and the more the flavor precursors. CONCLUSION: The black carp pickled products (with a weight of 20 g, with the size of 3 cm × 3 cm × 2 cm) is suggested to be steamed for 6 to 8 min. This conclusion provides a theoretical basis for its better taste quality. © 2020 Society of Chemical Industry.

Post-mortem quality changes of common carp (Cyprinus carpio) during chilled storage from two culture systems.

BACKGROUND: Omega-3 common carp (OCC) raised by patented culture systems have higher level of n-3 fatty acids and n-3/n-6 ratio than normal common carps (NCCs) from traditional culture system. Whether the patented farming system and modified fatty acid profile will influence OCC storage stability is unclear. This study aimed to expose the differences of post-mortem quality changes between NCC and OCC. RESULTS: NCC and OCC have similar rigor mortis patterns, only a higher level of lactic acid was observed in NCC after 96 h. Adenosine triphosphate (ATP) related compounds had no major differences, but slightly higher inosine monophosphate in OCC was found at 36 h. The K-value, Ki-value and Hx-index demonstrated high cohesiveness (Pearsons two-tailed, r = 0.968-0.984, P < 0.05) during storage, with statistically comparable (P > 0.05) temporal progress of change in NCC and OCC. The indices were lower in OCC than in NCC. Attenuation of myosin heavy chain in OCC was not as distinct as in NCC, coincided with its higher salt-soluble protein level at 144 h. Before 96 h, thiobarbituric acid value (TBA), total viable count (TVC), cooking loss (CL), drip loss (DL), and hardness in NCC and OCC were similar. However, at 144 h, higher TBA, TVC, CL and DL while lower hardness in NCC than in OCC were observed. Principle component analysis showed good separation of NCC and OCC in biplot at 0 and 144 h. CONCLUSION: Patented culture system has a slightly positive influence on post-mortem quality of common carp. It can be used for producing OCC without compromising storage stability. © 2020 Society of Chemical Industry.

Study on the Volatile Organic Compounds and Its Correlation with Water Dynamics of Bigeye Tuna (Thunnus obesus) during Cold Storage.

Volatile organic compounds (VOCs) and water play a key role in evaluating the quality of aquatic products. Quality deterioration of aquatic products can produce some off-odour volatiles and can induce water content changes. However, no previous study has investigated a correlation between water dynamics and VOCs of bigeye tuna during cold storage. The changes in VOCs, water dynamics and quality attributes of bigeye tuna (Thunnus obesus) upon storage at 0 °C and 4 °C for 6 days were investigated. The results showed that the values of ATP, adenosine diphosphate (ADP), adenosine monophosphate (AMP), T21 (trapped water) and the relative value of T1 decreased (p < 0.05), while drip loss and histamine contents increased (p < 0.05), which indicated quality deterioration during cold storage. With haematoxylin and eosin (HE) staining, muscle tissue microstructure was observed. VOCs such as hexanal, heptanal, 4-Heptenal, (Z)-, pentadecanal-, 1-pentanol, 1-hexanol significantly increased, which sharply increased the content of off-odour volatiles. T21 was positively correlated with 1-octen-3-ol, 1-penten-3-ol, while T21 was negatively correlated with hexanal, 1-hexanol. Therefore, good correlations between water dynamics and some VOCs were detected during quality deterioration of bigeye tuna throughout cold storage.

Effect of Specific Spoilage Organisms on the Degradation of ATP-Related Compounds in Vacuum-Packed Refrigerated Large Yellow Croaker (Larimichthys crocea).

This study examined the spoilage potential of specific spoilage organisms on the degradation of adenosine triphosphate (ATP)-related compounds in vacuum-packed refrigerated large yellow croaker. The total viable count (TVC), ATP-related compounds and related enzymes of vacuum-packed refrigerated large yellow croaker inoculated with different bacteria (Pseudomonas fluorescens and Shewanella putrefaciens) were characterized using the spread plate method, high-performance liquid chromatography and assay kits, respectively. Results indicated that the TVC for both control and Shewanella putrefaciens groups reached spoilage levels at days 9 and 15, respectively. The changes of adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP) and adenosine deaminase activity across all groups showed no significant difference attributable to microbial growth. The results suggested that ATP to inosine monophosphate (IMP) degradation primarily occurs via fish's endogenous enzymes, with minimal microbial involvement. On day 12, the IMP content in fillets inoculated with Pseudomonas fluorescens (0.93 µmol/g) was half higher than in those inoculated with Shewanella putrefaciens (0.57 µmol/g). Both spoilage organisms facilitated IMP degradation, with Shewanella putrefaciens making a more substantial contribution. Analysis of K values and correlation coefficients revealed that Shewanella putrefaciens was the primary factor in the freshness loss of refrigerated vacuum-packed large yellow croaker. These findings offer a reference for understanding quality changes in refrigerated large yellow croaker, especially regarding umami degradation at the microbial level.

Nonvolatile taste compounds of Shanghai smoked fish: A novel three stages control techniques.

In this work, the effect of processing stages including first soaking (FS), frying after first soaking (FFS), and second soaking (SS) on nonvolatile taste compounds of Shanghai smoked fish was investigated using high-performance liquid chromatography (HPLC) and automatic amino acid analyzer. Results showed that the contents of free amino acids (FAAs) ranged from 396.94 to 585.79 mg/100 g and 5'-inosine monophosphate (IMP, as main umami nucleotide) from 215.91 to 284.56 mg/100 g in Shanghai smoked fish, respectively. Moreover, the contents of Glu and Gly as main umami amino acids ranged from 1.64 to 107.32 mg/100 g and 61.61 to 108.88 mg/100 g, respectively. TAV values of IMP, Asp, and Glu in Shanghai smoked fish reached 11.38, 2.73, and 21.46, respectively. The obvious difference could be observed using principal component analysis (PCA) in three processing stages of Shanghai smoked fish. Therefore, probing into the nonvolatile flavor of Shanghai smoked fish could not only enrich the theoretical basis of flavor chemistry in freshwater fish fields, but probe into the formation mechanisms of taste compounds in further study.

Condition-dependent adenosine monophosphate decomposition pathways in striated adductor muscle from Japanese scallop (Patinopecten yessoensis).

The purpose of this study was to confirm inosine monophosphate (IMP) generation and to clarify the decomposition pathway of adenosine monophosphate (AMP) by investigating the properties of AMP, IMP, and adenosine (AdR) decomposition enzymes in Japanese scallop (Patinopecten yessoensis). The results showed that IMP accumulated due to AMP decomposition via endogenous enzymes in scallops stored at both 4 °C and 20 °C. The AMP decomposition rate was highest in the supernatant of homogenized scallop adductor muscle, followed by the suspended solution and precipitate, while IMP could not be decomposed in scallop. The results indicated that the activity of AdR deaminase was very high, and this enzyme was involved in an intracellular process in scallop. Moreover, 1 min of heating exerted little influence on the AMP and AdR decomposition rates, while 5 min of heating induced enzyme denaturation. The IMP generation rate increased dramatically in scallop crude enzyme solution containing 5 mM ethylenediaminetetraacetic acid (EDTA). This suggests that the major pathway of AMP decomposition might change with variations in metal ion concentrations in Japanese scallop. PRACTICAL APPLICATION: IMP generation in Japanese scallop (Patinopecten yessoensis) caused by endogenous enzymes was confirmed. IMP is very important for the umami taste (a pleasant savory taste) of aquatic products. As IMP accumulation might be achieved by changing the concentration of divalent metal ions and no IMP 5'-nucleotidase activity was detected in scallop, a suitable process to produce good flavor scallops with high IMP contents might be developed.

Effects of thawing methods on the biochemical properties and microstructure of pre-rigor frozen scallop striated adductor muscle.

Postmortem biochemical properties (pH, salt solubility, Ca2+-ATPase activity, ATP-related compounds) and microstructural changes in the striated adductor muscle of pre-rigor frozen Japanese scallops (Patinopecten yessoensis) were studied after thawing and during storage at 4℃. Four thawing methods were used: running water (18℃, R); ice-water (0℃, I); air (4℃, A) and ice-saltwater (-2℃, S). The pH values and salt solubility of R group were lower than the other three thawing groups while I group was highest after thawing. However, no significant difference (P < 0.05) in Ca2+-ATPase activity were detected among 4 groups. The microstructure results indicated that the structure of I group was close to that of fresh scallop. Moreover, ATP decomposition rate was the slowest. Therefore, ice-water thawing is the best method because it induced the least changes in the biochemical properties and microstructures of scallop adductor muscle.

Research on the quality changes of grass carp during brine salting.

The research on the quality changes of grass carp during brine salting with 6%, 8%, and 10% salt additions was evaluated by chemical and physical indicators, as well as a sensory assessment and microbiological analysis. The NaCl content was proportional to salt addition and salting time. The increase of salt addition could lead to the increase of hardness and chewiness in which change trends were contrary to the pH within 24 hr. All K values were less than 10% during brine salting. The effect of 8% salt additions on free amino acids was relatively smaller. Higher levels of salt additions could inhibit bacterial growth. Combined with sensory assessment, equivalent umami concentration (EUC), and taste activity value (TAV) to analysis comprehensively, it was suggested that grass carp meat should be eaten at 4-8 hr of brine salting with 8% salt additions or processed for the next step, in which the grass carp meat had a better taste and quality.

Research on the changes of water-soluble flavor substances in grass carp during steaming.

In this study, adenosine triphosphate (ATP)-related compounds and free amino acids were determined to study the changes of water-soluble flavor substances in grass carp meat during steaming for 18 min. Sensory assessment, electronic tongue, equivalent umami concentration (EUC) value, and taste active value (TAV) were also performed to obtain the best quality of steamed grass carp meat. The results showed that the flavor presented by nucleotides in three parts meat was better within 9 min. The bitter amino acids in the dorsal meat and red meat significantly decreased at 6 min (101.33 mg/100 g and 44.64 mg/100 g, respectively). From the sensory analysis, EUC value, and TAV, it can be found that the quality of grass carp meat was the best when steamed for 6-9 min. The electronic tongue indicated that the taste differences were significantly between 6 and 9 min. Therefore, this study suggested that grass carp should be eaten during 6-9 min of steaming. PRACTICAL APPLICATIONS: As the main way of meat processing and eating, heating not only endows the product with good color, but also kill microorganisms and improve the product quality. The reasonable heating will make the protein denaturation of the food, so that the protein digestion and absorption rate can be improved, which is conducive to people to obtain more abundant nutrition. The quality changes of grass carp meat during 18 min of steaming were studied by measuring ATP-related compounds and free amino acids, combining with sensory assessment, electronic tongue analysis, EUC value, and TAV. These results not only provide useful information for the quality control of grass carp in the heating process, but also provide theoretical reference for the improvement of the nutritional value of grass carp. In addition, the mechanism of flavor change in the heating process of grass carp will be further improved, and effective suggestions will be provided for consumers to reasonably eat grass carp.