Abstract:Studying the effect of yeast fermentation on the odor of Hypophthalmichthy nobilis can provide a certain theoretical basis for the processing of the fish. H. nobilis thin thorns and more meat and a strong earthy smell, which is less popular with consumers. Some of them are processed into frozen fish fillets, fish meal products and fish balls. The market is mainly for live sales, the utilization rate is not high, and a lot of waste is generated, which pollutes the environment and wastes resources. In recent years, the improvement of the organoleptic properties of fish and meat products through fermentation has received considerable attention. Traditional fermented fish is fermented under natural conditions by using microorganisms carried by the environment or by itself. The fermentation process is difficult to control and it is difficult to ensure that the number and types of microorganisms are the same, and the quality of fermented products varies greatly; furthermore, the product fermentation cycle is longer, resulting in fish meat the excessive oxidation of fatty acids reduces the nutritional quality of processed products. In addition, traditional fermented fish methods are diverse, processing environments vary greatly, product quality is unstable, and fermented flavors vary greatly. Raw materials, microbial activities, environment and other factors will affect the quality of fermented fish. The core technology is the breeding of microbial starters. Microbes play an important role in the physical, chemical, nutritional and sensory properties of fermented products. Therefore, research and development of related microbial starters to improve the quality of fermented fish products has practical significance. Appropriate processes are sought to improve the flavor quality characteristics of the products. At present, lactic acid bacteria are the most used in fish fermentation, because they produce acid during the fermentation process to reduce the pH value to inhibit the growth of other spoilage bacteria, and through acid-induced protein denaturation to enhance texture characteristics and improve taste. However, yeast, as another typical food industry probiotic, can produce more pleasant fruit aromas, but it has not been used in industrial fish products. This research uses silver carp as the research object, Saccharomyces cerevisiae as the fermenting agent, and combines headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) with electronic nose (E-nose) to study the odor changes during 3 and 5 days of fermentation. Results showed that after yeast fermentation, there were 12 kinds of esters, including nonanal, decanal, ethyl caproate, ethyl caproate, ethyl oleate and methyl formate, which gave the fish a ‘fruity aroma’ and ‘almond aroma’, so that the flavor substances were more abundant. After fermentation, the content of 1-octen-3-ol decreased by 16.04% and 18.09% after 3 and 5 days, which greatly improved the odor of H. nobilis. The E-nose and principal component analyses found that the different groups could be discriminated easily, indicating that the smell of the fish after the S. cerevisiae fermentation has changed greatly. The analysis of odor substance activity showed that there were 8 main odor substances after 3 days of fermentation, which was 3 more than that the group without adding S. cerevisiae, indicating that add S. cerevisiae can increase the main odor substances of silver carp. Ketones and hydrocarbons in different treatment groups also contributed to flavor, such as 3-octanone, 2-heptanone, caryophyllene, D-limonene, naphthalene, ethyl nonanoate, ethyl caproate, 2-octenol, etc.

Abstract:The annual output of large yellow croaker (Larimichthys crocea) in Fujian Province always exceeds 80% of the annual output in China. At present, L. crocea is mainly sold all over the country in the form of chilled storage. Therefore, it is important to prolong the shelf life of chilled L. crocea by taking the suitable pretreatment. Electrolyzed water has a high-efficiency and broad-spectrum bactericidal action, and its application in fish refrigeration preservation has been widely concerned. However, the effect of electrolyzed water pretreatment on the freshness, taste and odor of chilled L. crocea has not been reported. In order to investigate the effect of electrolyzed water pretreatment on quality changes of L. crocea during chilled storage, the total viable counts, total volatile basic nitrogen (TVB-N), ATP-related compounds contents, pH, hardness, color, taste and volatile odor of L. crocea pretreated by soaking in electrolyzed water with different available chlorine concentrations (50, 100, and 200 mg/L) and 1% NaCl solution were measured during storage at 4 ℃. The results show that, the initial total viable counts of L. crocea decreased from 2.30 to 1.83 lg(CFU/g), when the available chlorine concentration of electrolyzed water was 200 mg/L. After 16 day storage at 4 ℃, the TVB-N values of L. crocea muscle pretreated by electrolyzed water with the available chlorine concentration of 100 and 200 mg/L were 24.38 and 23.63 mg/100 g respectively, which were significantly lower than the control group (28.92 mg/100 g). The increases of HxR, Hx and K values in the fish muscle were retarded by electrolyzed water pretreatment, and the inhibitory effect was increased with the increase of available chorine concentration. No significant differences were observed in the pH and hardness of fish muscle with and without electrolyzed water pretreatment. The yellowness b^* value of fish muscle was increased with the increase of available chorine concentration under the same condition for 16 day storage. The bitterness, aftertaste-B and richness of fish muscle increased gradually with increasing storage time, while the umami, saltiness and sweetness decreased. The taste values of aftertaste-B and saltiness in fish muscle pretreated with electrolyzed water were higher than those in the control group. The volatile odors in fish muscle pretreated by electrolyzed water with the available chlorine concentration of 200 mg/L were decreased during 4-10 day storage, but were higher than those in the control group after 16 day storage at 4 ℃. In conclusion, electrolyzed water pretreatment can be effective in inhibiting the microbial growth and freshness decline of L. crocea during chilled storage. The inhibition effect of electrolyzed water was related to its available chlorine concentration. However, after being pretreated by the electrolyzed water with high available chlorine concentration, L. crocea is easy to turn yellow and produce volatile odors during chilled storage. The results of present study provide a theoretical reference for the selection of electrolyzed water with suitable available chlorine concentration in the preservation of chilled L. crocea.

Abstract:In order to explore the quality differences of the new variety "Huahai No.1" Megalobrama amblycephala cultured in different modes, this study took "Huahai No.1" M. amblycephala with different culture modes (pond culture and lake culture) as the research object; their appearance and texture were determined by colorimeter and texture analyzer, and their nutritional characteristics and flavor compounds were determined by ultra performance liquid chromatography (UPLC) or gas chromatography-mass spectrometry (GC-MS). The results showed that the brightness, whitenes as well as the springiness, chewiness and resilience of flesh in M. amblycephala cultured in lake mode were significantly higher than those of those cultured in pond mode, and the muscle moisture content of the lake group was higher and the crude fat content was lower. The EAA/TAA and EAA/NEAA ratios of fish in pond group and lake group were 0.41, 0.82 and 0.38, 0.72, respectively, which were in line with the ideal essential amino acid composition recommended by FAO/WHO. Although the index of essential amino acids in the pond group were higher than that in the lake group, only lysine content in the essential amino acids as significantly higher than that in the lake group, while the contents of non-essential amino acids and semi-essential amino acids of fish in the lake group were 1.05 times and 1.01 times that in the pond group, respectively. The total fatty acid content in the lake group decreased by 21.09%, and the proportion of polyunsaturated fatty acids increased by 4.00%, among which EPA and DHA content were 14.20 times and 7.51 times those in the pond group, and the nutrition of the fish in the lake group was more balanced. The TAV values of glutamic acid and alanine in pond group were greater than 1, while that of lysine in lake group was greater than 1, but the total proportion of fresh and sweet amino acids in fish in lake group was higher, and the total proportion of bitter amino acids was lower, and the contents of umami-presenting AMP and IMP in lake group were 1.24 times and 1.54 times those in pond group, while Hx and HxR in bitter taste were only 62.74% and 44.53% of those in pond group. Combined with sensory evaluation, the interaction of flavor substances made the lake group fish fresh and sweet, and the content and ROAV value of volatile compounds such as (Z)-cis-4-hepten-1-al and 1- hexanol which negatively affect the odor in fish meat of lake group were lower, and the odor quality was better. In sensory evaluation, the scores of texture, color, taste and smell were significantly higher in lake group, which was consistent with the above results. The above results indicate that the material quality, nutritional quality and flavor quality of M. amblycephala in the lake culture mode are better than those in the pond culture mode, which can be promoted as a better culture mode.This study provides a theoretical basis for selecting the appropriate culture mode to improve the muscle quality of "Huahai No.1" M. amblycephala.

Abstract:Sea cucumber is a traditional nutritious marine food and an important economic aquatic product in China. Sea cucumbers are vulnerable to autolysis, and most sea cucumbers require processing before distribution and consumption. Therefore, processing is a critical sector in the industry chain of sea cucumber. Clarifying the change in the composition and food structure of sea cucumber during processing is the key point for understanding the mechanism of sea cucumber product quality, and would direct the rational development of novel technology for the high-quality processing of sea cucumber. It is thus considered as a key scientific issue related to the development of the sea cucumber industry. In this review, the composition and food structure features of sea cucumbers were overviewed, and the major processing procedures of sea cucumbers were summarized. Based on this background, the changes in composition and food structure of sea cucumber during the processing, including boiling, drying, rehydration, enzymatic hydrolysis, and ready-to-eat sea cucumber processing were introduced, and the recommendations for further research were provided. It would be beneficial for accelerating the solution of the above scientific issue, and contribute to the high-quality development of the sea cucumber industry.

Abstract:Crispness is one of the most important indexes for Ctenopharyngodon idella. Over-crispy C. idella will show hemolysis, hypoxia and pathological changes of some organs. Therefore, it is urgent to develop method to detect the crispness of C. idella. In this paper, a method based on Raman spectroscopy was proposed to detect the crispness of C. idella. Firstly, the Raman spectra of C. idella with different crisping time were analyzed by PCA method. The results showed that Raman spectroscopy could be used to identify the crispness of crispy C. idella with different crisping time. Additionally, with the extension of the crisping time, the α-helix of the total protein in the muscle of crispy C. idella was decreased, while the β-fold of the total protein in the muscle of crispy C. idella was increased. In terms of irregular curl of the total protein in the muscle of C. idella, obvious changes were observed at the early stage, but not at the late stage of crisping. Secondly, four preprocessing methods, including SG, SNV, MSC and Normalize, were used to preprocess the Raman spectrum data. It was found that Normalize method had the optimal preprocessing effect, with RMSEP of 2.33 and R²_P of 0.73. Thirdly, PLSR, SVR and BPNN were used to establish the relationship model between crispness and Raman spectrum information from the muscle of C. idella. The RMSEP of the prediction set was 2.33, 2.26 and 1.96 , respectively, and the R²_P of the prediction set was 0.73, 0.78 and 0.83, respectively. Apparently, the BPNN model was the optimal one. Taken together, our results showed that the Normalized-BPNN prediction model based on Raman spectroscopy could effectively detect the crispness of C. idella. This study paves a new way for C. idella muscle crispness detection methods in the future.

Abstract:Aquaculture is an important way to meet people's demand for protein in the future. Reducing the decline in the quality of post-harvested fish and shellfish is an important topic in the field of aquatic product processing. Striated muscle is the main edible part in the muscle of fish and shellfish, and its energy metabolism state affects muscle quality. This article reviews the energy metabolism of striated muscles, including the production, transport and consumption of ATP. A series of muscle freshness evaluation indexes proposed based on the energy metabolism process of striated muscle were reviewed,including K value, K_max value and AEC value of ATP and its related compounds, as well as the ATPase activity, mitochondrial structure and respiratory activity of myogenic fibronectin and sarcoplasmic reticulum. The applicability of each freshness index in iced fish and live shellfish was further summarized according to the consumption status, and the necessity and urgency of strengthening the control of fish and shellfish in the early of post-harvest stage (quality determination period) were put forward. Among many indicators, mitochondrial activity can be used as an effective indicator for quality control in the quality determination period, facilitate effective carry out quality evaluation in the perishable period, and reduce quality loss and resource consumption caused by improper post-harvested disposal. And provide a theoretical support for promoting that sustainable development of the aquatic product industry.

Abstract:In order to understand the pollution status and ingestion risk of heavy metals in seafood and fresh water products in eastern coastal areas, 12 kinds of seafood and 8 kinds of fresh water products on the market were analyzed in this study. Microwave digestion-inductively coupled plasma mass spectrometry (ICP-MS) method was used to determine five kinds of common heavy metals, including lead, cadmium, mercury, arsenic and chromium. The pollution degree was evaluated according to single factor pollution index (P_i) and metal pollution index (MPI), the content difference of heavy metals in different aquatic products and pollution status were compared, and the health risk was evaluated by target hazard quotients (THQS). The test results show that the lead content in seafood and freshwater products was in the range of ND-1.100 mg/kg, the lead exceeding rate was 1.4%, and the average lead content of each species had no significant difference (P>0.05); the range of cadmium content was ND-1.600 mg/kg, the cadmium exceeding rate was 2.8%, and the average content of cadmium in Crassostrea gigas and Argopecten irradians was higher than other varieties (P<0.05); the mercury content range was ND-1.900 mg/kg, the average total mercury content of Thunnus maccoyii was higher than other species (P<0.05), and there was no significant difference in the average total mercury content of other species (P>0.05); the range of total arsenic content was 0.004-4.100 mg/kg, and the average total arsenic content of freshwater fish (except Channa argus) was lower than other species (P<0.05); the chromium content range was 0.010-32.000 mg/kg, the chromium exceeding rate was 2.3% and the average chromium content of Aristichthys nobilis was higher than other species (P<0.05). The single-factor pollution index showed that: different types of aquatic products have certain pollution; the heavy metal pollution index shows the trend of seawater shrimp and crab>seawater shell>freshwater shrimp and crab>sea fish>freshwater fish. The health risk assessment showed that except for T. maccoyii, the health risk values of marine products and freshwater products were less than 1.0, and the risk when eating was relatively small. The results of this study show that seafood and freshwater products in the eastern coastal areas have a certain degree of heavy metal pollution, but the pollution is lighter and the intake risk is relatively small.

Abstract:Myofibril-bound serine proteinase (MBSP) is a serine proteinase which binds closely to myofibrillar proteins and is ubiquitous in animal muscle. MBSP is effective in the degradation of myofibrillar proteins, including myosin heavy chain (MHC), α-actinin, actin, and tropomyosin (TM) and is thus regarded as an important proteinase responsible for the metabolism of fish muscle in vivo, and is also considered as one of the main endogenous proteases causing the modori phenomenon. However, most research on fish MBSP focused on freshwater fish, and the research on MBSP from marine fish is still quite limited. In this study, the gene of MBSP from yellow croaker (Larimichthys crocea) was predicted by bioinformatics. Recombinant protein (Lc-rMBSP) was obtained by gene cloning and construction of pichia pastoris expression system. Enzymatic properties of Lc-rMBSP including molecular weight, substrate specificity, optimum temperature and pH were analyzed and its secondary structure was detected by circular dichroism. The three-dimensional structure of Lc-MBSP was analyzed by homology modeling. Sixteen trypsin-like genes in the genome of yellow croaker were identified. Phylogenetic tree analysis and multi-sequence alignment were performed between these genes and MBSPs in freshwater fish. The highest homology (57%) gene sequence (Lc-MBSP) was thus obtained, which had an open reading frame of 735 bp encoding 244 amino acid residues. The molecular weight of the recombinant protein Lc-rMBSP was~28 ku, and its optimal temperature and pH were 50 ℃ and 8.0, respectively. Circular dichroism analysis showed that temperature had a great influence on its secondary structure, and the thermal denaturation was irreversible. The thermal denaturation temperature of Lc-rMBSP was (62.82±1.09) ℃, suggesting it is a thermally stable proteinase. Lc-rMBSP showed high hydrolytic activity toward MHC and TM in a temperature range of 40~60 ℃. Lc-rMBSP hydrolyzed substrate Boc-Leu-Lys-Arg-MCA most effectively, and it specifically cleaved substrates containing arginine residues on the carboxyl side, which was similar to MBSP from Saurida undosquamis. The three-dimensional structure of Lc-MBSP was obtained by homology modeling. Its catalytic triplet was His-61, Asp-105 and Ser-198; its substrate binding pocket (Ser-192, Gly-215 and Ser-225) was slightly different from common trypsin-like proteinases, which was quite possibly the main reason for the difference in substrate specificity between Lc-rMBSP and other trypsins. Our present work provides a theoretical reference for the investigation of MBSP from marine fish.

Abstract:Crayfish (Procambarus clarkii) is one of the most important economic crustacean species in China. In 2020, the area farmed P. clarkii was 0.14 million hectares, with production exceeding 2.39 million tons, which ranked the 6th among freshwater aquaculture species in China (the top 5 are all large freshwater fish species). As an important and popular freshwater aquatic product in China, the food safety of P. clarkii is widely concerned by consumers. Trace element level is an important index to evaluate food safety. In order to investigate the concentrations of trace elements in rice-crayfish and its food safety, 24 trace elements in 156 samples of P. clarkii cultured in rice fields in Hubei, Hunan and Anhui were detected by inductively coupled plasma mass spectrometry (ICP-MS). Crayfish cultured in rice fields of Hubei, Hunan and Anhui three provinces were collected from May to June in 2021. A total of 156 samples were collected, including 55 from Hubei province, 56 from Hunan province and 45 from Anhui province. The pollution levels and potential health risks were estimated by pollution indices, exposure assessment and non-carcinogenic risk assessment method. Twenty trace elements had been detected in P. clarkii samples, and Li, Be, Tl and U were not detected. The contents of 17 trace elements with a detection rate of more than 50% were in order from high to low: Zn>Fe>Cu>Rb>Al>Mn>Sr>Ba>Se>As>Mo>Cs>Ag>V≈Cr>Co>Ga. The average content of Zn was the highest (5.384±4.650 mg/kg), followed by Fe [(3.153±1.898) mg/kg] and Cu [(2.459±0.919) mg/kg]. Except Rb and Al, the content of essential trace elements in muscle of P. clarkii was higher than that of harmful trace elements. Sixteen of the 24 trace elements in the rice-crayfish samples had significant differences between Anhui and other two provinces, and 5 of them had significant differences between the three regions. The contents of 6 heavy metals (Cu, Zn, As, Cr, Pb and Cd) in crayfish samples were lower than those reported in previous studies. The possible reason was monitoring time, location and other factors, especially the sampling site. Some trace elements in rice-crayfish muscle showed significant regional differences by phylogenetic relation analysis, which indicated that the enrichment of trace elements in aquatic products was related to the growing environment. The pollution indices of five toxic heavy metals (As, Cu, Pb, Cd and Cr) in rice-crayfish samples from three provinces were all lower than 0.2 and at safe levels. The estimated daily intakes(EDI) of 7 elements (Cu, Zn, Cr, Al, As, Pb and Cd) were 1.213, 2.656, 0.003, 0.899, 0.030, 0.0005 and 0.00005 μg/(kg·d), respectively. The intake of the 7 elements accounted for 0.125%-10.862% of the ADI values of adults. Consumption of Cu, Zn, Cr, Al, As, Pb and Cd from P. clarkii in the survey area was associated with low health risk. Except for Fe element (THQ=1.111), the THQ values of other 20 elements were all lower than 1, and the total target hazard quotient (TTHQ) was 3.672. TTHQ was lower than 10, which indicated that the P. clarkii muscle samples analyzed in this study had no toxic risk effect. However, Fe intake is of concern.

Abstract:Post-harvest fish suffer slow and painful deaths by asphyxiation, crowding, or even crushing. Stress and stress-related quality changes of farmed fish is necessary to explore. Instead of live fish in poor condition at the market, providing freshness-locked products with sushi-grade near to upper-limited quality of farmed fish is more valuable. In order to establish a technical system for post-fishing regulation of freshness of factory farmed fish, the formation and change mechanism of sashimi grade quality of mariculture white meat fish were analyzed from the point of limit quality. The brown flounder (Paralichthys olivaceus) was taken as the research object. The limit of muscle quality was explored via different slaughter methods. That is, extreme treatment was used to explore the upper limit of fresh quality. The upper limit of quality was obtained by spinal cord destruction treatment (SCD), and the lower limit of quality was obtained by suffocation in air treatment (SA). The two limits of quality were compared with the spinal cord cut treatment (SCC), which is in wide commercial use. The three slaughter treatment groups were refrigerated at 2 ℃ for 120 h. During this period, rigidity, breaking strength, muscle shrinkage, muscle pH, ATP and its related compounds, whiteness, microstructure and surface color were analyzed. The results showed that the effects of slaughter stress on quality and stability were very important. The SA group with the strongest slaughter stress rapidly got into postmortem rigidity after 6-12 h and then the stiffness was relieved. The SCD group with the lowest slaughter stress reached the maximum postmortem rigor from 48 h to 72 h, and the rigor index increased slowly, showing the best stability of cold storage. The SCC group of conventional commercial disposal was between the two groups, and the quality was significantly better than the lower limit quality of SA group and inferior to the upper limit quality of SCD group. Similarly, the lowest slaughter stress group retained the highest ATP, and the ATP content in muscles decreased from 3.13 μmol/g to 2.13 μmol/g in SCD group, compared with the 1.99 μmol/g in SCC group and 0 μmol/g in SA group at postmortal 12 h after slaughter, respectively. The time to drop to the limit pH in muscles was 48 h in the SCD group, 48 h in the SCC group, and 12 h after death in the SA group. The results of observation and colorimetric analysis showed that the strongest slaughter stress SA group had the worst muscle appearance, showing the lowest L^* value, higher a^* value and lower b^* value. The microscopic structure of the muscle showed that the intercellular space was the largest and most unstable in the SA group. The effects of slaughter stress intensity can also be obviously observed on the surface of fish body. The greater of stress, the more serious of congestion in fins. In conclusion, spinal cord destruction disrupts the motor nervous system with minimum stress intensity, minimizes muscle movements caused by spinal reflexes, and minimizes slaughter stress in living P. olivaceus , which is the key factor to meet the limit quality. This study provides a reference for controlling slaughter stress to obtain the best quality.

Abstract:Currently, food allergy has become a food safety issue of global concern, and there is no effective cure at home and abroad. Avoiding the intake of allergens is the best solution to prevent food allergies; therefore, the construction of a rapid and sensitive allergen detection system is of great research significance to ensure the safety of consumers. A colloidal gold immunochromatographic method was established with tropomyosin (TM) of Litopenaeus vannamei as the detection target for the rapid detection of major allergens TM in crustacean aquatic products. SD rats and New Zealand rabbits were immunized with natural TM to prepare polyclonal antibodies. Then, the immunochromatographic test strips were assembled based on the double antibody sandwich principle using 40 nm colloidal gold labeled rat anti-TM IgG as detection antibodies and rabbit anti-TM IgG as capture antibodies for the detection of commercial food samples. The test strip can display the results within 5 min with a 10 ng/mL visual detection limit. The developed immunochromatographic test strips showed high specificity to crustacean, such as shrimp, crab, Procambarus clarkii and Homarus americanus, although there is a weak cross reaction with clams and scallops. The recoveries of standard addition in commercial food products without crustaceans were 81%-126%, indicating the method's high accuracy. The intra-and inter-batch coefficient of variation of the test strip was less than 15%. Additionally, the test results of the actual food samples were consistent with the food allergen label. The results show that the developed method possesses sufficient sensitivity and specificity. Therefore, it can effectively detect crustacean residues in a variety of matrices and commercial food samples and has strong practical application value.

Abstract:Pseudomonas spp. are specific spoilage bacteria of various fish from freshwater and marine during aerobic chilled storage. The behavior of psychrotrophic Pseudomonas is one of the common causes of quality deterioration in refrigerated fish products. P. fluorescens as a typical psychrotrophic spoilage bacterium, is main dominant spoilage Pseudomonas in aquatic product. Whole genome sequence analysis of genetic information is helpful to understand the molecular basis of spoilage, drug resistance and adaptation of foodborne spoilage bacteria. Currently, about 30 strains of P. fluorescens with complete genome map have been published in NCBI database, of which only an isolate P. fluorescens PF08 comes from Scophthalmus maximus. To explore the strong spoilage potential and environmental adaptability of P. fluorescens, the proteolytic activity and total volatile basic nitrogen (TVB-N) production of two isolates of P. fluorescens PF07 and PF08 from marine fish were measured and the mechanisms of spoilage and adaptation were explored deeply by comparative genomics. P. fluorescens PF07 and PF08 showed strong proteolytic activity and produced high TVB-N in refrigerated fish juice. After sequencing, assembly and functional annotation of whole genome, the length of the PF07 genomic was 6.13 Mb, and GC content was 61.4%. According to pan genome analysis, there were 4980 core genes in the two isolates, and 516 and 470 unique genes in PF07 and PF08, respectively. The highest proportion of genes was involved in amino acid metabolism both in the two isolates by COG and KEGG annotations, while the most unique genes belonged to inorganic ion transport and metabolism in PF07. Glycosyltransferases and glycoside hxydrolases genes accounted for the highest proportion among carbohydrate active enzyme in the two genomes based on CAZy annotation. In addition, many genes of enzymes and related protein associated with degrading various substrates of carbohydrates, proteins, and lipids were founded, such as alkaline metalloproteinase AprA, polyamine ABC transporter permease PotC, arginine and ornithine decarboxylase, etc. Several genes of sigma factors, including rpoS, rpoN and rpoD, were also distributed in the two strains. Two P. fluorescens isolators indicated strong spoilage potential, and had many genes encoding protease and putrescine formation and amino acid metabolism, and decomposing glycogen and fat, were distributed in the two isolates, as well as environmental adaptation regulators. This work preliminarily clarified the molecular basis of P. fluorescens with strong degradation of fish nutrition substrates at the genetic level, and revealed the metabolic characteristics and spoilage mechanism in P. fluorescens, which will provide a theoretical basis for exploring the spoilage mechanism of Pseudomonas in aquatic fish.

Abstract:To explain the preservation mechanism of bamboo leaf antioxidant soaking combined with whey protein isolate coating on Se-rich rainbow trout (Oncorhynchus mykiss) at the protein level with physicochemical properties of protein. The Se-rich O. mykiss was cut longitudinally to fillets after beheading, gutting, and skinning. The Se-rich rainbow trout fillets (SRTFs) were immersed in 1.0% antioxidant of bamboo leaves (AOB) solutions (distilled water served as the control) followed by coating with whey protein isolate (WPI), then stored at 4 ℃ for 1, 4, 7, 10 and 13 d after the surface moisture on SRTFs was drained at 25 ℃. The myofibrillar protein and TCA-soluble peptides contents, and molecular bond, as well as total sulfhydryl content, surface hydrophobicity, and secondary structure of myofibrillar protein were measured, to investigate the effect of coating on the physicochemical properties of protein from Se-rich O. mykiss during cold storage. The results showed that the myofibrillar protein and β-sheet contents for the WPI group were significantly higher than the control during cold storage. From 1 to 7 days, the TCA-soluble peptides and disulfide bond contents, and surface hydrophobicity index (H₀) for the WPI group were significantly lower than the control, while total sulfhydryl content showed an opposite trend. However, these differences between the WPI group and control gradually weakened as the cold storage time prolonged, and there was no significant difference at 13 d. The myofibrillar protein, total sulfhydryl, hydrogen bond, α-helix, and β-sheet contents for the 1.0% AOB+WPI group were higher than the WPI group and control, while an opposite trend was observed for H₀ and the contents of TCA-soluble peptides, disulfide bond, and β-turn. The WPI film was formed on the surface of SRTFs, which can isolate the fillets from the air and alleviate microbial contamination. AOB contains flavonoids, polyphenols, etc., which can scavenge free radicals and inhibit the oxidation of sulfhydryl groups and the formation of disulfide bonds, leading to the delay of myofibrillar protein denaturation. In addition, the hydrophilic groups in polyphenols can reduce the surface hydrophobicity of myofibrillar protein and improve the solubility. These results indicated that AOB soaking combined with WPI coating inhibited the denaturation and degradation of myofibrillar protein, resulting in the delay of the quality attributes deterioration of SRTFs during cold storage.

Abstract:In order to explore the difference in flavor of dried Trachinotus ovatus fillets with different drying methods, chilled T. ovatus fillets were selected as raw materials in this study. Three drying method were applied in the drying process, including hot air drying, heat pump drying, and freeze drying and the TBA value, nucleotide content, free amino acid content, and volatile flavor substances were measured and analyzed. The results were compared between different drying method groups and the chilled fish group. The results showed that the TBA value and K value of the T. ovatus fillets increased significantly after drying. The TBA value of freeze dried fish was only 1.6 times higher than that of chilled fish fillets, but heat pump drying and hot air drying increased the figure by 5.5 and 4.5 times respectively. After drying, the total free amino acid content and MSG equivalent of the fish were significantly lower than those of the chilled fish fillets. The MSG equivalent of hot air dried fish has dropped by 50.83%. The bitter amino acid content and the umami amino acid content in the heat pump dried fish accounted for 19.11% and 7.37% of the total amino acid content, respectively. Among the three drying methods, the MSG equivalent of 4.47 g MSG/100 g of heat pump dried T. ovatus fillets is the highest, indicating that the heat pump dried T. ovatus fillets has the highest umami degree. In terms of volatile flavor components, heat pump dried fish contains more esters and ketones, which mainly present the flavors of fruits and roasted nuts. In hot air dried fish, the relative content of hydrocarbons and aromatics is about 70%, and the relative content of aldehydes and esters is 20%. In freeze dried fish, the relative content of hydrocarbons and aromatics accounted for more than 90% of the total, and the aldehyde and esters are less than 8%, so its flavor is relatively weak. In summary, the T. ovatus fillets processed by three drying methods had good eating quality. Among them, heat pump drying makes the umami taste in the fish more obvious. Freeze drying can effectively inhibit the oxidation of fat and is more suitable for the fish with high fat content. This provides a technical reference for the processing of light and dry food for the T. ovatus.

Abstract:In order to investigate the effects of sleep deprivation duration on the level of oxidative stress in mice and the intervening effect of the oligopeptide SEP-3 from skipjack (Katsuwonus pelamis) on oxidative stress in sleep deprived mice, male C57BL/6 mice were first subjected to sleep deprivation for 0, 48 and 72 h by modified multi-platform water environment method, respectively. The effects of sleep deprivation time on oxidative stress in mice were evaluated by detecting the T-AOC, MDA content, SOD and GSH-Px activity in serum and liver of mice. Then C57BL/6 male mice were divided into normal group, SD group (sleep deprivation group), melatonin group (20 mg/kg melatonin), SEP-3 group and ★SEP-3 group (50 mg/kg SEP-3). All groups were deprived of sleep for 72 h except normal group. The effects of SEP-3 on oxidative stress in sleep-deprived mice were evaluated by changes in body weight, liver morphology and T-AOC, MDA content, SOD and GSH-Px activity in serum and liver of mice. The research found that the levels of MDA and SOD in serum of mice were significantly increased after sleep deprivation for 48 hours, while T-AOC and GSH-Px were not significantly changed. T-AOC, SOD and GSH-Px activity in liver showed a decreasing trend, while the content of MDA showed an increasing trend. After 72 h sleep deprivation, T-AOC, SOD and GSH-Px activity in serum and liver of SD group mice decreased significantly, while MDA content increased significantly. Drug intervention can significantly increase T-AOC, SOD and GSH-Px activity in serum and liver of mice, and reduce MDA content. There were no significant differences in MDA content, SOD and GSH-Px activity in serum and liver between oligopeptide groups and positive control group. However, the serum T-AOC in positive control group was significantly higher than that in oligopeptide groups, but there was no significant difference between oligopeptide groups. In liver, there was no significant difference in T-AOC between positive control group and ★SEP-3 group, but both groups were significantly higher than SEP-3 group. In addition, the drug had no effect on the body weight of sleep-deprived mice, but had significant protective and repair effects on liver injury, and the positive control group and SEP-3 group had better effects. The research indicated that the oxidative stress response was significantly activated in mice after 72 hours of sleep deprivation, and SEP-3 significantly improved the oxidative stress injury induced by sleep deprivation. This study provides a theoretical basis for the development of medication for sleep disorders or health food for adjuvant therapy.