Characterization of the flavor profile and dynamic changes in Chinese traditional fish sauce (Yu-lu) based on electronic nose, SPME-GC-MS and HS-GC-IMS.

In this study, flavor characteristics and dynamic change of Chinese traditional fermented fish sauce (Yu-lu) with different fermentation time (2, 4, 6, 8, and 12 months) were analyzed. The electronic nose analyses confirmed a notable flavor change in fish sauce samples from different stages. During the 12-months fermentation, the total volatile compounds in fish sauce increased from 3.9 mg/L to 13.53 mg/L. Acids, aldehydes, esters and phenols were the main aroma substances and their contents gradually increased during the fermentation process. The PCA of GC-MS and GC-IMS showed that fish sauce samples from different fermentation periods can be well distinguished. A total of 110 volatile compounds identified by GC-MS, and 102 volatile compounds were detected by GC-IMS. Among them, 13 compounds were identified by both GC-MS and GC-IMS. The most varieties (49) of volatiles appeared after 8 months of fermentation. The odor activity value (OAV) analysis showed that 10 volatile compounds were considered as characteristic flavor in traditional fish sauce. The variable influence on projections (VIPs) in PLS-DA models constructed by GC-MS and GC-IMS identified 5 and 10 volatile compounds as biomarkers, respectively. Our results revealed the dynamic changes of characteristic flavor in fish sauce in combination of GC-MS and GC-IMS, which provides theoretical basis for the production and flavor regulation of fish sauce.

Fish species authentication in commercial fish products using mass spectrometry and spectral library matching approach.

Seafood fraud has become a global issue, threatening food security and safety. Adulteration, substitution, dilution, and incorrect labeling of seafood products are fraudulent practices that violate consumer safety. In this context, developing sensitive, robust, and high-throughput molecular tools for food and feed authentication is becoming crucial for regulatory purposes. Analytical approaches such as proteomics mass spectrometry have shown promise in detecting incorrectly labeled products. For the application of these tools, genome information is crucial, but currently, for many marine species of commercial importance, such information is unavailable. However, when combining proteomic analysis with spectral library matching, commercially important fish species were successfully identified, differentiated, and quantified in pure muscle samples and mixtures, even when genome information was scarce. This study further tested the previously developed spectral library matching approach to differentiate between 29 fish species from the North Sea and examined samples including individual fish, laboratory-prepared mixtures and commercial products. For authenticating libraries generated from 29 fish species, fresh muscle samples from the fish samples were matched against the reference spectral libraries. Species of the fresh fish samples were correctly authenticated using the spectral library approach. The same result was obtained when evaluating the laboratory-prepared mixtures. Furthermore, processed commercial products containing mixtures of two or three fish species were matched against these reference spectral libraries to test the accuracy and robustness of this method for authentication of fish species. The results indicated that the method is suitable for the authentication of fish species from highly processed samples such as fish cakes and burgers. The study shows that current and future challenges in food and feed authentication can efficiently be tackled by reference spectral libraries method when prospecting new resources in the Arctic.

Effect of ozone oxidation on gastrointestinal digestion and absorption characteristics of silver carp (Hypophthalmichthys molitrix) surimi gels in vitro.

To investigate the quality of different ozone-oxidized surimi gels and their in vitro digestion and absorption characteristics, surimi rinsed with different concentrations of ozonated water (0, 8, 26 mg/L) were prepared. Then, the degree of oxidation and gel structure of surimi were determined, the in vitro digestion and absorption of the gels were simulated, and the digestion and absorption products were analyzed by LC-MS/MS. The results showed that the quality of surimi gels was improved after proper ozone oxidation. After ozone water rinsing, the dry matter digestibility, peptide, and amino acid content increased, and the changes of all three were in line with the Logistic kinetic model (R2 = 0.95-0.99). Caco-2 cell absorption experiments showed that the absorption rate of peptides and amino acids decreased after ozone water rinsing. In summary, ozone oxidation can promote the digestion of surimi gels, but it also reduces the absorption of peptides and amino acids by Caco-2 cells. This study provides a reference for the application of ozone in the food field.

Se and Hg in processed fish-derived products and their fish raw materials: Occurrence, Se:Hg molar ratio, HBVSe index, bioaccessibility and Caco-2 cells toxicity.

Processing conditions applied during food production could affect food component contents and bioaccessibility. Here, possible changes in Hg and Se total and species contents and bioaccessibility have been tracked in each stage of the production chain of processed fish-derived products. Therefore, Se:Hg molar ratio and Selenium Health Benefit Value (HBVSe) were calculated for final products and raw materials, resulting favorable in all cases, suggesting the safety of surimi-based products regarding mercury. Speciation studies revealed the presence of SeMeSeCys and SeMet in all samples. Thus, the integrity of the selenium species seems to be maintained. Moreover, in vitro gastrointestinal digestion model evidenced that Se bioaccessibility ranged between 20-39 % for all samples, while in case of Hg was between 8-37 %. Additionaly, SeMeSeCys and SeMet were also identified in the gastrointestinal extracts. Finally, no cytotoxicity was observed after exposure of Caco-2 cells to the gastrointestinal extracts.

Evaluation of fish meal freshness using a metal-oxide semiconductor electronic nose combined with the long short-term memory feature extraction method.

To improve the classification and regression performance of the total volatile basic nitrogen (TVB-N) and acid value (AV) of different freshness fish meal samples detected by a metal-oxide semiconductor electronic nose (MOS e-nose), 402 original features, 62 manually extracted features, manually extracted and selected features by the RFRFE method, and the features extracted by the long short-term memory (LSTM) network were used as inputs to identify the freshness. The classification performance of the freshness grades and the estimation performance of the TVB-N and AV values of fish meal with different freshness were compared. According to the sensor response curve, preprocessing and feature extraction steps were first applied to the original data. Then, five classification algorithms and four regression algorithms were used for modeling. The results showed that a total of 30 features were extracted using the LSTM network, and the number of extracted features was significantly reduced. In the classification, the highest accuracy rate of 95.4% was obtained using the support vector machine method. In the regression, the least squares support vector regression method obtained the best root mean square error (RMSE). The coefficient of determination (R2), RMSE, and relative standard deviation (RSD) between the predicted value of TVBN and the actual value were 0.963, 11.01, and 7.9%, respectively. The R2, RMSE, and RSD between the predicted value of AV and the actual value were 0.972, 0.170, and 6.05%, respectively. The LSTM feature extraction method provided a new method and reference for feature extraction using an E-nose to identify other animal-derived material samples.

A hyperstable, low-salt adapted protease from halophilic archaeon with potential applications in salt-fermented foods.

Salt-tolerant proteases with remarkable stability are highly desirable biocatalysts in the salt-fermented food industry. In this study, the undigested autocleavage product of HlyA (halolysin A), a low-salt adapted halolysin from halophilic archaeon Halococcus salifodinae, was investigated. HlyA underwent autocleavage of its C-terminal extension (CTE) at temperatures over 40 °C or NaCl concentrations below 2 M to yield HlyAΔCTE. HlyAΔCTE demonstrated robust stability over a wide range of -20-60 °C, 0.5-4 M NaCl, and pH 6.0-10.0 for at least 72 h. Notably, HlyAΔCTE is the first reported halolysin with such exceptional stability. Compared with HlyA, HlyAΔCTE preferred high temperatures (50-75 °C), low salinities (0.5-2.5 M NaCl), and near-neutral (pH 6.5-8.0) conditions to achieve high activity, consistently with its production conditions. HlyAΔCTE displayed a higher Vmax value against azocasein than HlyA. During fish sauce fermentation, HlyAΔCTE significantly enhanced fish protein hydrolysis, indicating its potential as a robust biocatalyst in the salt-fermented food industry.

Various factors affecting the gel properties of surimi: A review.

As an important aquatic prepared food, surimi products are favored by consumers due to their unique viscoelastic properties and high nutritional value. Gel properties are the main indicators to measure the quality of surimi products. The gelation of surimi mainly involves intramolecular (conformational change) and intermolecular (chemical force) changes. Factors such as processing treatments, raw fish species and exogenous additives affect surimi protein structure, chemical forces and endogenous enzyme activities, which further affect the gel properties of surimi products. This review focuses on the mechanism of surimi heat-induced gel, mainly including protein chain expansion and aggregation through various chemical forces to form a three-dimensional network structure. In addition, the mechanism and application of different factors on the gel properties of surimi were also discussed, providing a reference for the selection of fish species, the control of heating conditions in the gel process of surimi products, the selection of additives and other measures to improve the gel performance.

Multi-layered structure and physicochemical properties of reconstituted meat-based products from minced fish by physical extrusion: Impact of extrusion strength.

Multi-layered structure of reconstituted meat-based products from minced fish was formed by physical extrusion, followed by an investigation into the impact of extrusion strength on structural and physicochemical properties before and after frying. Under an appropriate pressure (3-9 kPa), the air within minced fish underwent enrichment and rearrangement to form a stratified phase, promoting the formation of multi-layered structure during frying. Conversely, the lower pressure (≤1.5 kPa) was insufficient for phase separation and directional rearrangement, while the higher pressure (≥15 kPa) would cause the stratified phase to flow out of food system. Moreover, by directly increasing water mobility and meat compactness, physical extrusion indirectly caused more water loss and stronger ionic bonds during frying, which was positively correlated with multi-layered structure. However, an excessive pressure caused an increase in random coil and hydrophobic interactions during frying, which was negatively correlated with multi-layered structure. In conclusion, appropriate physical extrusion strength promoted the formation of multi-layered structure.

Comprehensive insights into the mechanism of flavor formation driven via inoculation with mixed starter cultures in dry-fermented tilapia sausages: Integration of macrogenomics, volatilomics, and lipidomics.

To investigate the mechanisms of flavor formation in dry-fermented tilapia sausages, the volatiles, bacterial community, and lipid composition during fermentation were analyzed using gas chromatography-ion mobility spectrometry, 16S high throughput sequencing, and ultra-performance liquid chromatography-mass spectrometer. Pediococcus pentosaceus, Staphylococcus xylosus, and Staphylococcus carnosus became dominant bacteria during the fermentation. A total of 66 volatiles and 293 lipids (48 differential lipids) were identified. PC and PE content decreased. Aldehyde and 1-octen-3-ol content decreased. Most esters and ketones content increased during fermentation. Six metabolic pathways associated with differential lipids were identified by enrichment analysis. Glycerophospholipid metabolism was the main metabolic pathway. Correlation analysis revealed that PC and PE were precursors for volatiles, including PC 16:0/18:2 and PE 18:0/22:6. The dominant bacteria facilitate the hydrolysis of PC and PE, leading to the formation of esters and ketones. This study provides a theoretical basis for the targeted regulation of fermented sausage flavors.

Metaproteomic Analysis of Microbial Communities Affecting Fishery Products.

Fishery products are one of the main human nutritional sources, and due to the consumption increase, the quality of the derived products may be modified, during catching, technological processing, and storage. Detection and identification of pathogenic and spoilage microorganisms in fishery products is needed because the first may be involved in human diseases, while the second is responsible of significant economic losses. In this sense, liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) method and computational analysis of MS data are useful tools for characterizing and identifying different microorganisms and to develop promising strategies for food science investigations. Moreover, in the past decade, metaproteomic methodologies have progressed for the study of microorganisms isolated from their natural samples and independently of the culture restrictions. Metaproteomics enables assessment of proteins and pathways from individual members of the consortium. Metaproteomics can provide a detailed understanding of which organisms occupy specific metabolic niches, how they interact, and how they utilize nutrients, and these insights can be obtained directly from environmental samples.According to that, the sample preparation of the fishery product, the LC-ESI-MS/MS dedicated method, and the MS data analysis were described in the present chapter to obtain the metaproteomic analysis of the respective microbiomes or microbial communities.

κ-Carrageenan masking bitterness perception in surimi gels containing potassium chloride-based salt substitutes: Gel properties, oral processing, and sensory evaluation.

κ-Carrageenan (CG) was employed to mask the bitterness induced by 50% KCl in surimi gels to achieve salt reduction and gel performance improvement. The combination of KCl and CG (KCl + CG) yielded the increased textural characteristics and water-holding capacity (WHC) of surimi gels and facilitated the transition of free water to immobilized water. In addition, the KCl + CG supplement increased the turbidity and particle size of myofibrillar protein (MP) sols but decreased the surface hydrophobicity in a dose-dependent manner. The hydrophobic interactions and disulfide bonds played crucial roles in maintaining the stability of MP gels. The specific binding of potassium ions to the sulfate groups of CG limited the release and diffusion of potassium ions from the surimi gels during oral processing, effectively masking the bitterness perception and maintaining the saltiness perception. This study provides a promising strategy to reduce the utilization of sodium salt in surimi products.

A review of inhibition mechanisms of surimi protein hydrolysis by different exogenous additives and their application in improving surimi gel quality.

It is well known that aquatic products such as fish and shellfish, when stored for a long period of time under inappropriate conditions, can suffer from muscle softening. This phenomenon is mainly caused by endogenous proteases, which are activated during heating and accelerates the degradation of myofibrillar proteins, directly leading to weaker gels and poorer water retention capacity. This paper reviews the changes in fish proteins during storage after death and the factors affecting protein hydrolysis. A brief overview of the extraction of protease inhibitors, polysaccharides and proteins is given, as well as their mechanism of inhibition of protein hydrolysis in surimi and the current status of their application to improve the properties of surimi.

Changes in protein and volatile flavor compounds of low-salt wet-marinated fermented Golden Pomfret during processing.

In this experiment, the changes in protein hydrolysis, protein oxidation, and flavor of low-salt wet-marinated fermented golden pomfret were studied during processing. During processing, a decrease in sulfhydryl content (P < 0.05), a significant increase in protein surface hydrophobicity (P < 0.05), a significant increase in carbonyl content and TCA-soluble peptide (P < 0.05), an increase in TVB-N and amino acid nitrogen (P < 0.05), and a significant increase in the content of free amino acids (P < 0.05), indicating that proteins were gradually oxidized and degraded to small molecules and flavor precursors under the action of bacterial reduction pretreatment, deodorization, marination and fermentation processes, small molecules and aroma precursors was generated by gradual oxidative decomposition. In the course of processing, a total of 113 volatile flavor compounds were identified using GC-MS analysis, while OPLS-DA analysis and VIP value determination led to the identification of 10 characteristic flavor compounds. The results showed that an abundance of flavor compounds was generated during the processing, thereby imparting a more pronounced taste profile to the low-salt wet-marinated fermented golden carp. The results showed that a large number of flavor substances were generated during the processing to give a richer flavor to low-salt wet-marinated fermented golden pomfret that could provide data and theoretical support for the subsequent processing industry of golden pomfret.

Characteristics and stabilization of Pickering emulsions constructed using myosin from bighead carp (Aristichthys nobilis).

Myosin from bighead carp (Aristichthys nobilis) as a main type of fish protein possesses a good emulsifying ability. However, whether bighead carp myosin (BCM) could construct stable Pickering emulsions is still unclear. Therefore, myosin particles and Pickering emulsions stabilized by bighead carp myosin (BCMPEs) were analyzed. The surface structure of BCM particles at 0.6 mol/L NaCl treatment was uniform and compact with a contact angle of 86.4 ± 2.7°, exhibiting the potential ability to construct O/W Pickering emulsions. The size and flocculation index (FI) of BCMPEs decreased with the increase in BCM concentrations of 1%-4% (w/v). Reversely, the size of BCMPEs increased with the increase in oil-water ratios. BCM particles could uniformly distribute at the oil-water interface to stabilize BCMPEs at a BCM concentration of 4% (w/v) and an oil-water ratio of 6:4 (v/v). This study could help explore fish proteins to construct Pickering emulsions for the deep processing of fish products.

Effect of modified cellulose-based emulsion on gel properties and protein conformation of Nemipterus virgatus surimi.

Microcrystalline cellulose was modified by TEMPO oxidation combined with ultrasound to prepare modified cellulose-based emulsion. The effect of different emulsion concentration on gel properties and protein conformation of surimi was investigated. The results showed the length and width of microcrystalline cellulose were reduced, and a large amount of -COOH was introduced into modified cellulose. Direct addition of flaxseed oil decreased the gel strength and WHC from 3640.49 g·mm and 76.94% to 2702.95 g·mm and 75.89%, respectively, while 5% modified cellulose-based emulsion could improve the gel properties of surimi. Surimi gel containing 5% emulsion had the highest hydrophobic interaction, disulfide bond and ß-sheet content. Moreover, protein network structure was the densest in 5% emulsion group. Therefore, modified cellulose-based emulsion could be used to compensating for the negative impact of direct addition of flaxseed oil on surimi, which provided a new idea for the development of healthy and new emulsified surimi products.

The effect of ohmic heating conditions and heating modes on gel properties of unwashed pre-rigor common carp (Cyprinus carpio) surimi.

Ohmic heating (OH) at different conditions (voltage: 15, 20, 25 V; frequency: 1, 5, 10 kHz) and one-step water bath (WB) were used to heat wash and unwash surimi prepared from fresh pre-rigor common carp. The optimal heating conditions were established through assessments of gel strength, Texture Profile Analysis (TPA), water-holding capacity (WHC), whiteness, and sensory evaluation. Then, the impact of heating modes on gelation properties of unwashed surimi based on the optimal heating conditions was investigated. The study findings indicated a significant enhancement in gel properties compared to WB. Unwashed surimi gel properties showed improvement when derived from freshly caught raw fish and subjected to OH treatment. Moreover, variations in frequencies and voltages were observed to influence the heating rate. Optimal gel quality was achieved at 10 kHz 20 V (10 V/cm), facilitating swift progression through the gel deterioration stage, inhibition of protein hydrolyzing enzymes activity, and establishment of a stable gel network. Continuing to increase the heating rate would disrupt its network structure, resulting in diminished gel strength and WHC. The best quality of unwashed surimi gel was achieved by heating to 40°C for 30 min, followed by heating to 90°C for another 30 min (40°C 30 min + 90°C 30 min) under 10 kHz 20 V. The gel strength increased when held for 1 h at 40°C. For optimal heating efficiency, the heating mode of 40°C 30 min + 90°C 30 min is recommended to prepare unwashed surimi gel. PRACTICAL APPLICATION: Ohmic heating, as a rapid food heat treatment method, can both increase the heating rate and improve the gelation properties of freshwater surimi. There is a wide range of potential applications for the heat treatment of the surimi.

The impacts of cold plasma on the taste and odor formation of dried silver carp products.

This study investigated non-thermal pretreatment (cold plasma, CP) on the flavor (taste and odor) profiles of dried fish products. CP treatment of 5 min contributed to accumulation of umami nucleotides adenosine 5'-monophosphate (AMP) from 30.96 to 40.82 µg/g and inosine 5'-monophosphate (IMP) from 2009.29 to 2132.23 µg/g, and significant reduction of bitter hypoxanthine ribonucleoside (HxR) and hypoxanthine (Hx), respectively (P < 0.05) in the dried fish products. A noticeable enhancement in sweet glycine (from 429.41 to 490.03 mg/100 g) and umami glutamic acid (from 55.68 to 67.76 mg/100 g) accompanied with the CP treatment (P < 0.05) based on taste activity value (TAV > 1). And the characteristic odor volatiles (nonanal, hexanal and 1-octen-3-ol) were strengthened 2.13-, 2.16- and 2.17- folds, respectively (P < 0.05). The results of equivalent umami concentration and Gibbs free energy calculation, combining with the correlation analysis, indicate that nucleotides and free amino acids synergically enhanced the taste improvement of dried fish products. Moderate lipids oxidation favored the formation of characteristic volatiles. The CP pretreatment offered new strategies for enhancing flavor of dried fish products.

Perilla juice and ginger juice reduced warmed-over flavor (WOF) in surimi gels: Due to the inhibition of the formation of the WOF compounds and the masking of the WOF.

The effects and reasons of perilla juice (PJ) and ginger juice (GJ) on the reduction of "warmed-over flavor" (WOF) in surimi gels were revealed by detecting odor profiles and protein and lipid oxidation degrees of surimi gels, concentrations and odor activity values (OAVs) of WOF compounds. Adding PJ and GJ to surimi gels significantly reduced the WOF and improved the fish fragrance odor, but sodium ascorbate (SA) only weakened the WOF. The (E,E)-2,4-heptadienal's OAVs in the PJ and GJ groups were decreased by >50% compared with the control check (CK) and SA groups. Meanwhile, surimi gels added with PJ and GJ presented lower lipid and protein oxidation degrees. The verification test indicated that PJ and GJ's aroma had a masking effect on the WOF. In conclusion, PJ and GJ reduced the WOF in surimi gels by preventing WOF compounds' production and masking the WOF with their distinct aroma.

Modification of myofibrillar protein structural characteristics: Effect of ultrasound-assisted first-stage thermal treatment on unwashed Silver Carp surimi gel.

The hardness properties of unwashed surimi gel are considered as the qualities of gelation defect. This research investigated the effect of ultrasound-assisted first-stage thermal treatment (UATT) on the physicochemical properties of unwashed Silver Carp surimi gel, and the enhancement mechanism. UATT could reduce protein particle size, which significantly reduced from 142.22 µm to 106.70 µm after 30 min of UATT compared with the nature protein. This phenomenon can promote the protein crosslinking, resulting in the hardness of surimi gel increased by 15.08 %. Partially unfolded structure of myofibrillar protein and exposures of tryptophan to water, lead to the increase in the zeta potential absolute value, driven by UATT. The reduced SH group level and the conformational conversion of proteins from random coiling to α-helix and ß-sheet, which was in support of intermolecular interaction and gel network construction. The results are valuable for processing protein gels and other food products.

Mercury levels in Nile perch fillets in processing industries in Uganda.

Mercury levels of Nile perch fillets to be exported from selected fish processing industries in Uganda were determined by hot digestion in strong acids, followed by analysing the extracts with Inductive Coupled Plasma-Mass Spectroscopy (ICP-MS). There was a clear link between atmospheric mercury and methylmercury accumulation in fish tissues, thus exposing a possible threat for human health. A quantitative cross-sectional study design was undertaken from two fish processing factories around Kampala city. Simple random sampling was utilised where ten fish products were picked for analysis. The results obtained from the analysis of samples from both factories presented mercury levels far below the FAO/WHO guideline level of 0.5 mg/kg for mercury in fish. The mercury levels for both factories were higher than the oral daily recommended dose of 0.001 mg/kg body weight for the vulnerable population raising eyebrows for the general population, since fish is a major contributor to mercury intake for consumers.