Abstract:Tilapia is an important species of aquaculture in China. It is widely used in aquatic product processing due to its tender meat, less bones and low price. The main products are fillet and frozen fish. Fish pre-treatment process is complex. The key links include descaling, head removal, viscera removal and cleaning, etc. Fish descaling machine refers to a kind of mechanical equipment to remove the scales of fish body by using the scale-scraping structure. It is usually used for batch processing small and medium-sized fish or processing large fish one by one. Descaling machine can use the methods including water jet, scraper, brush, mesh-plates, etc. The descaling machine can be divided into intermittent type and continuous type according to the feeding mode. The roller structure is one of the effective methods for fish descaling. Scraper, mesh-plate and other structural parts are installed in the inner wall of the drum. Descaling is realized under the interaction between the fish body and the inner wall of the drum while the drum is rotating. Compared with water jet, roller descaling has the characteristics of large handling capacity and good continuity of production. In the actual production, the final production effect will be affected by the type of structural parts, the structure of the drum and the actual production operation. This paper focuses on exploring the practical effect and influencing factors of different components in the process of drum descaling. Four common descaling structures are selected such as steel mesh, punched mesh, angle cutter and rebar. A drum descaling experimental device was designed to carry out the research on the technological parameters of the tilapia drum descaling. The descaling rate and damage degree were measured under different test conditions. On this basis, a multi-drum descaling device was designed and tested. The results show that: Descaling time and drum speed are the main parameters affecting the descaling effect of expanded metal lath and punched mesh. The descaling rates with different descaling time were significantly different (P < 0.05), and the descaling rates increased with the increase of time. The descaling rate can reach 95% when the drum speed is 35 r/min and the descaling time is close to 4 min. Descaling effect of angle steel cutter at different drum speeds is significantly different (P < 0.05). The descaling rate can reach up to 90% when the drum speed is about 35 r/min. Thus it can be seen that angle steel cutter suitable for fish descaling processing onalarge scale. The resulting damage is significantly increased, although increasing the tool angle can improve the descaling effect. The descaling effect of rebar at different drum speeds is significantly different (P < 0.05). The descaling rate increases with the increase of rotating speed. The descaling rate can reach up to 90% when the drum speed is increased to 55 r/min. The damage of fish body mainly includes mouth damage, fin damage, surface scratch and other types. The damage degree increased with the increase of descaling time. The optimum parameters of tilapia drum descaling device are 35 r/min and 3 min. According to the descaling effect, expanded metal lath and punched mesh were selected to form a multi-drum descaling device. Under the experimental conditions, the descaling rate was up to 95% after 3 min of processing, and the damage was low. The combination of different descaling functional parts can effectively improve the descaling effect and reduce the damage. This study obtained the best roller descaling process parameters used for tilapia. It provides the basis for the improvement and optimization of tilapia drum descaling equipment.

Abstract:Pyropia is one of the most commercially important marine algae. Pyropia cultivation of China ranks first in the world, but the production value remains low. Porphyran is the major polysaccharide from Pyropia. It consists of alternating 4-linked α-L-galactopyranose-6-sulfate (L6S) residues and 3-linked β-D-galactopyranose (G) residues. Porphyran and its degradation products were confirmed to have various bioactivities, which is considered as an important way to realize the high-value application of Pyropia. In order to explore the glycoside hydrolase for degrading porphyran and verify the feasibility of its application, here, a porphyranase coding gene por16B was cloned from the marine bacterium Wenyingzhuangia fucanilytica and heterologously expressed in Escherichia coli. The biochemical properties and hydrolysis patterns of the recombinant protein Por16B_Wf were characterized. Por16B_Wf exhibited maximum activity at 40 °C and pH 7.0, and it possessed stable activity under different pH conditions. Por16B_Wf hydrolyzed porphyran by an endo-acting manner. The end products of Por16B_Wf were mainly composed of porphyran disaccharides L6S-G. The subsite specificity of Por16B_Wf was clarified by glycomics strategy. It specifically hydrolyzed the β-1,4 glycosidic linkage of G-L6S, whereas it tolerated 3,6-anhydro-α-L-galactopyranose and methyl-D-galactose in subsites –2 and +2, respectively. Furthermore, Por16B_Wf was applied in the compound enzymolysis of Pyropia. Compared with the classical enzymolysis technique of Pyropia using neutral protease, the compound enzymatic hydrolysate was characterized with low viscosity (8.5 Pa·s) and high conversion rate (79.4%±0.3%) of Pyropia. Por16B_Wf could be utilized as a promising tool for the degradation of porphyran. In this study, the compound enzymolysis of Pyropia was realized for the first time, which was beneficial to the full development of Pyropia, and provided new insights into the deep-processing and high-value utilization of Pyropia.

Abstract:Sea bass (Lateolabrax japonicus) is an economically important marine species widely cultured in fisheries worldwide. During storage and transportation, L. japonicus are susceptible to be deteriorated due to the combined effects of microorganisms and endogenous enzymes, resulting in the change of freshness and protein biochemical, which affects its edible value. Therefore, it is particularly important to ensure its quality and safety by taking the appropriate regulation methods of fish quality changes during storage and transportation. In this study, the quality parameters including texture, color, and freshness parameters including thiobarbituric acid, K-value, total volatile based nitrogen, total viable count and sensory score, and the protein biochemical characteristics (myofibrillar protein content, secondary structure, sulfhydryl and carbonyl content) were measured periodically to analyze the effect of epigallocatechin gallate (EGCG) and agar oligosaccharide (AO) on the freshness of sea bass fillets during ice storage. The results showed that the total number of colonies and K values of the control group at the 16th day were as high as (6.78±0.15) lg (CFU/g) and 67.37%±1.75% respectively, and the sensory score was lower than 8, indicating the fillets were inedible at this time. While the samples of EGCG group (EG), the agar oligosaccharide group (AO) and the composite group can maintain value of the hardness, color, and other freshness related index. The TBA value of the control group were as high as (0.81±0.03) mg/kg after post mortem 20 days. However, the TBA values of the EG group, AO group, and composite group did not increase significantly during storage, and were always lower than the control group. In addition, the carbonyl content of the control group was significantly higher than that of other treatment groups from 12 days (P<0.05), and increased to (1.63±0.04) nmol/mg at the end period of storage, while the carbonyl content of the EG group, AO group and composite group was only (1.14±0.03), (1.28±0.08) and (0.99±0.09) nmol/mg respectively. The contents of protein, and sulfhydryl of the composite group samples were (70.58±2.02) mg/g and (39.39±0.99) μmol/g prot, respectively, which were higher than those in the control group and other treated groups at 20 days. The value of α-helix were15.38%±0.55%, 15.30%±1.85%, and 18.47%±0.74% in EG group, AO group, and composite group at 16 days, respectively, which were significantly higher than that of control with 13.26%±0.51%. The value of random coil was increased from the initial vale of 13.97%±0.91% to 24.36%±2.57% when storage for 16 days, while the value of composite group was only 16.75%±0.99%, indicating that the treatment of EG and AO suppressed the disordered changes of proteins.The results showed that EGCG and agar oligosaccharide had both good preserve effect, which could maintain the freshness of fish fillets, and significantly inhibit protein denaturation and oxidation of proteins. EGCG combined with agar oligosaccharide had better preservative effect than the single preservative, and extend the shelf life to more than 20 days. This research provides a theoretical basis for the preservation mechanism of EGCG and agar oligosaccharide and a reference for the development the novel efficient biological preservatives.

Abstract:The influence of cassava starch on the 3D printing effect of Nemipterus virgatus surimi was investigated in three aspects: apparent viscosity and rheological properties (transport capacity), printing effect (appearance morphology, stereotypy), and gelation properties of surimi products, using Nemipterus virgatus surimi as the research object, by adding cassava starch, the gel properties of surimi products can be improved, the water holding capacity and elasticity can be improved. Low field nuclear magnetic analysis, rheological analysis and molding effect analysis were used to determine gel strength, texture characteristics, water holding capacity, water distribution and composition, apparent viscosity and dynamic rheology. The results demonstrate that with the increase of cassava starch addition, the gel strength, hardness, flexibility and water holding capacity of the Nemipterus virgatus surimi slurry showed a trend of rising first and then decreasing, reaching the highest value at 2% of cassava starch addition, which increased by 113.63%, 249%, 28% and 9.14%, respectively, compared with the control group. The relative content of immobilized water (T₂₃) in the surimi reached the highest value at 2% of cassava starch addition, with a T₂₃ peak ratio of 0.98. The apparent viscosity and yield stress of surimi slurry increased with the increase of cassava starch addition, and the elastic modulus (G') and loss modulus (G'') of the slurry tended to increase first and then decrease with the increase of cassava starch addition, reaching the highest at 3% of tapioca concentration, and the loss tangent (tanδ) reached a maximum at 2% of starch concentration. In summary, when cassava starch addition was 2%, the effect of surimi 3D printing was the best. This study has positive guidance for 3D printing of surimi, and provides some reference for realizing the practicality, extensiveness and diversification of 3D printing in the food field.

Abstract:Ulcerative colitis recently has become an increasingly common disease worldwide, mainly due to people’s unbalanced daily diets. The effects of three different marine lipids, namely eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA), on ulcerative colitis mice and influences on their intestinal flora were studied. In the present study, the C57BL/6 mice were used as experimental model, induced by dextran sulfate sodium (DSS); The protective effects of these three kinds of marine lipids on ulcerative colitis were evaluated by the indexes of the body weight loss, disease activity index (DAI) score, the morphology of colon, the length of colon, the ratio of colon weight to length, the microscopic images of colon sections stained with hematoxylin-eosin (H.E) and histological damage score; 16S rDNA high-throughput sequencing method was adopted to characterize the influences of these three marine lipids on the microecological changes of intestinal flora in mice. DAI of EPA, DPA, DHA and model group increased 0.33-3.33, 0.33-2.67, 0-3.00, 0.33-4.00 respectively; length of colon tissue increased by 21.12%, 21.90% and 22.29% in EPA, DPA and DHA group compared to model mice (5.16 cm); the ratio of colon weight to length of EPA, DPA and DHA group reduced by 22.18%, 22.15% and 24.55% compared with model mice; mice treated with EPA, DPA and DHA showed lower histological damage score (2.51, 2.16, 2.23 respectively) while DSS treated mice showed worse intestinal morphology (3.51). The results of pathological indexes showed that the decrease of body weight, the increase of DAI, the shortening of the colon tissue and the increase of histological damage score were significantly inhibited by the supplementation with these three kinds of marine lipids, compared with the model group. Moreover, DPA was more effective in the prevention of the loss of body weight, the increase of disease activity index score and the increase of the histological damage score than EPA and DHA. Higher abundance of Akkermansia, Alistipes, Bifidobacterium, Blautia, Butyricicoccus, Eubacterium and Oscillibacter and lower abundance of Allobaculum, Bacteroides, Desulfovibrio, Enterococcus, Esherichia/Shigella, Lactococcus, Prevotella and Lachnospiraceae were showed in mice treated with EPA, DPA and DHA by 16S rDNA high-throughput sequencing, compared with the model group. The results represented the significantly regulatory effect of these three kinds of marine lipids on intestine flora ecology. In addition, DPA was more effective in the regulation of the relative abundance of Akkermansia, Alistipes, Butyricicoccus and Esherichia/Shigella, compared with EPA and DHA. All these findings indicated that EPA, DPA and DHA, these three kinds of marine lipids could significantly alleviate the symptoms of UC, and the composition and structure of intestinal flora in UC mice were significantly affected by the supplementation of these three kinds of marine lipids. Based on these, we assumed that the regulation effect of these three kinds of marine lipids on UC was related to their regulation effect on the specific intestinal microorganisms. We hope this study could provide important reference for the research of biological effects of marine active lipids, especially for the biological effects of DPA. Moreover, we hope this study could also provide important reference for the dietary control of chronic diseases.

Abstract:To prolong the shelf life of Se-rich rainbow trout, the fillets of Se-rich Oncorhynchus mykiss were respectively immersed into three antioxidant solutions of bamboo leaves (AOBS, 0.5%, 1.0%, and 1.5%), then coated using whey protein isolate solution (WPIS). The fillets coated were stored at 4 °C for 1, 4, 7, 10, and 13 d after the surface moisture was dried. The pH, TVB-N, and K values, total viable count (TVC), and total psychrophilic bacterial count (TPC) were measured, as well as moisture content and moisture state, to investigate the effect of coating on quality attributes of Se-rich O. mykiss during cold storage. The results showed that as cold storage time prolonged, the pH, TVB-N, and K values, TVC, and TPC of fillets significantly increased, while the moisture content significantly decreased (P<0.05). Besides, the bound water/immobilized water was transferred to free water. The pH, TVB-N, and K values, TVC, and TPC of fillets for 1.0% AOBS+WPIS group were lower than those for the other groups, as well as the percentage of bound water/immobilized water was transferred to free water, while the moisture content was higher than that of the other groups. These results suggested that the combination of whey protein isolate and antioxidant of bamboo leaves significantly enhanced the fresh-keeping effect of whey protein isolate coating, inhibited the quality deterioration and prolonged the shelf life of Se-rich O. mykiss. Furthermore, according to TVB-N and K values and TVC, 1.0% AOBS+WPIS group could prolong the shelf life 3 days for Se-rich rainbow trout at cold storage. The results can provide scientific reference for the low-temperature storage of Se-rich O. mykiss.

Abstract:The current freshwater fish grading methods are simple and unrepeatable. This paper was aimed to provide a grading method for refrigerated grass carp fillets. The color, odor, morphology, texture of raw grass carp fillets and the odor, taste and broth turbidity of boiled grass carp fillets were used for sensory description analysis. According to principal component analysis (PCA) and hierarchical cluster analysis (HCA), the freshness grading of refrigerated grass carp fillets was provided. Physical and chemical indicators including the K value and biochemical indicators such as desmin and troponin T were compared with specified sensory properties. The evaluation of the grading method was given. According to the results of PCA and HCA based on sensory description, refrigerated grass carp fillets can be divided into three freshness levels: 0-1 d (first-level freshness), 2-7 d (second-level freshness), and 8-10 d (three-level freshness). The relative gray values of desmin and troponin T decreased to 95.68 % and 96.75 % at the end of first-level freshness; to 56.4 % and 69.6 % at the end of second-level freshness; to 56.36 % and 52.85 % at the end of third-level freshness respectively. HCA reflected by physical and chemical indicators was consistent with that by specified sensory indicators, indicating that specified sensory properties could reflect the change of freshness of freshwater fish. Troponin T had a similar trend in the change and a potential as freshness indicator. This study provided freshness grading ranges based on specified sensory indicators, and macle an evaluation. On this basis, the relationship between the change of desmin and troponin T, and HCA reflected by specified sensory indicators was investigated. Troponin T could reflect the freshness of refrigerated grass carp fillets effectively. This provides a foundation for developing testing paper for fish in future.

Abstract:Aquatic product processing industry has a large scale in China, but the field of deep processing is weak. The functional lipids of aquatic products represented by EPA and DHA are important targets for deep processing of aquatic products. Hair loss originates from the imbalance between hair shaft regeneration and shedding. EPA/DHA-enriched triglyceride (EPA/DHA-TG) and blue light irradiation can both promote hair regeneration, however the effect of EPA/DHA-enriched phospholipids (EPA/DHA-PLs) on hair regeneration and its interaction with blue light irradiation are still unclear. In the present study, artificial hair removal mice were used to establish a hair regeneration model and to explore the effects of dietary supplementation with EPA/DHA-PLs combined with blue light irradiation on hair regeneration. After the back hair removal, male Kunming mice were randomly divided into four groups (n=8), including white light irradiation group, blue light irradiation group, and blue light irradiation combined with dietary supplementation with DHA-PLs or EPA-PLs group. The length and coverage of regenerating hair were measured, and HE staining was applied to observe the morphology and number of hair follicles. The mRNA and protein expression levels of genes related to hair regeneration were analyzed to preliminarily explore the possible underlying mechanism. The results showed that with the blue light irradiation, dietary supplementation with EPA/DHA-PLs could significantly increase hair length and coverage. Specially, the effect of DHA-PLs was better than EPA-PLs in the early stage of hair regeneration, and the effect of EPA-PLs is more prominent compared with DHA-PLs in the later stage, which might be related to the regulation of hair follicle cycle, the increased expression of vascular endothelial growth factor (VEGF), and the regulation of fibroblast growth factor 18 (Fgf18). This study suggested that dietary supplementation with EPA/DHA-PLs could enhance the promotion effect of blue light irradiation on mouse hair regeneration, which may provide a scientific basis for the use of aquatic functional lipids in the health maintenance of hair.

Abstract:Rice mash fish is one of the traditional fermented fish products in China, with unique flavor, taste and bright color. However, shortcomings such as long fermentation time, low safety, short storage period and inconvenient consumption, limit its commercial development. Modern biological fermentation technology (inoculated fermentation) can effectively shorten the fermentation time and improve the safety, while thermal sterilization technology provides a way for prolonging the storage life and for being convenient ready-to-eat. In order to explore the sterilization process of inoculated rice mash grass carp, the influence of key technological parameters such as drying degree and sterilization condition on physicochemical property, sensory property and preservation quality was analyzed in this study. The results showed that the water activity (Aw) of the final product was 0.86, 0.82 and 0.78, under the drying degree of 63.48%, 55.37% and 47.76%, respectively. At the F-value of 5 min, the bulgy product was observed after sterilization treatment at 90 ℃ and 95 ℃. When F-value was more than 6.5 min, the product was commercially sterile. At the same time, a* value significantly increased (P < 0.05) with the increase of sterilization temperature, while no obvious changes were observed in L* value, b* value and shear force (P > 0.05). The highest sensory score was 84.9 at the sterilization temperature of 95 ℃ with 17.4 min. During the 120 d storage period, Enterobacteria was not detected in the products both stored at 4 ℃ and 25 ℃, and the product stored at 4 ℃ had a better sensory quality. Therefore, the optimal sterilization conditions for inoculated rice mash grass carp are as follows: F=6.5 min, T= 95 ℃, t=17.4 min, and the storing period under this treatment can reach 120 days. In conclusion, reasonable drying degree, sterilization conditions and storage temperature can effectively improve the quality of inoculated rice mash grass carp during the storage. This paper could practically promote the processing and utilization of grass carp and improve the quality of sterilized ready-to-eat aquatic products.

Abstract:In order to investigate the changes of physiological and biochemical indexes and flesh quality of turbot (Scophthalmus maximus) during transportation in water and without water to provide reference for the preservation and transportation of S. maximus, in this study, turbots were placed under water and waterless conditions for simulated transportation experiments to compare the changes of physiological and biochemical indexes and muscle quality of S. maximus in different transportation environments and to provide reference for the preservation of S. maximus in transportation. In the experiment, the purchased S. maximus was temporarily reared, cooled, oxygenated and packed for transport, and samples were taken from S. maximus at different times of transport to test the physiological and biochemical indexes and muscle indexes of S. maximus. The results showed that after 18 hours of simulated transportation, the survival rate of S. maximus in the water transport group and the waterless transport group remained 100%. The water content, crude fat, pH, glycogen, adenosine triphosphate (ATP) and adenosine monophosphate (AMP) contents in S. maximus muscle decreased significantly, lactate and inosine monophosphate (IMP) contents increased. Among them, the AMP content of S. maximus in the group transported in water decreased by 38.65% and the IMP content increased by 29.1%, while the AMP content of turbot in the group transported without water decreased by 12.83% and the IMP content increased by 28.47%; among the blood biochemical indexes of S. maximus, blood glucose (GLU), blood urea nitrogen (BUN) and cortisol levels increased significantly. After transportation, the changes of physiological stress and energy metabolism indexes of turbot in the waterless transportation group were smaller than those in the water transportation treatment group. In addition, the content of flavorful nucleotides IMP and AMP in the muscle of turbot in the low-temperature anhydrous transportation group was significantly higher than that of S. maximus in the water transportation group, indicating that the low-temperature anhydrous transportation increased the flavorful substances of turbot and improved the flavor of fish flesh. The results of the study indicate that the application of low-temperature waterless keep-alive technology for live fish transportation has broad prospects.

Abstract:With the continuous growth of population, the human society needs more and more natural resources. So far, human has focused on exploiting available resources from land, ignoring the importance of marine resources. The ocean covers 71 percent of the earth's surface, with the countless resources available in the ocean with a great value for development. Therefore, the significance of marine resources is becoming more prominent, including marine food resources. As a result, more and more countries are exploring to get the nutrients and health benefits for humans from marine foods, so the rational development and utilization of aquatic resources has become an important part of China's sustainable food development strategy. Aquatic products are not only superior in quantity, but also can provide a variety of nutrients for humans, including high-quality protein, unsaturated fatty acids, vitamins, minerals and others, playing a key role in ensuring global food nutrition and food security. In addition, although land is also rich in natural bioactive substance resources from terrestrial plants, animals or microorganisms, many Marine products can produce a variety of unique natural biological active substances due to the complex living environment, including peptides, polysaccharides, alkaloids, and so on. For example, chitosan derived from shrimp and crab is the only cellulose with positively charged active group in nature, which can effectively remove negatively charged harmful substances in human body. And these marine active substances can also play a supplementary and strengthening role in human health, it has benefits ranging from the development of brain and intelligence to the prevention of cardiovascular disease and cancer. On this basis, we believe that aquatic resources can complement terrestrial resources well for human’s nutrition and health demand. Therefore, we put forward the philosophy thought of "the complementation of sea and land, a balance of Yin and Yang", and we reviewed the advantage of aquatic product nutrition composition and its important effect in medicine and health. The scientific utilization of aquatic products to regulate the diet structure of residents and the development of marine health products are prospected. To provide theoretical basis for the further development of the nutritive and sanitarian function of aquatic products and value orientation, and comprehensively promote the complementation of aquatic resources with terrestrial resources, to better serve the construction of human health. The reasonable intake of aquatic products to balance daily diet of high fat, high protein, high calorie, to further ensure food safety and promote the national healthy diet. Based on the nutritional value of aquatic products, the basic nutrients and special fatty acids which are rich in aquatic products are fully developed and utilized to optimize the intake of nutrients and build a new healthy diet pattern. In addition, relying the comprehensive cooperation of marine biotechnology, food science, medicines and other multi-disciplinary to research and develop high quality sea medicines and health products has precise effect based on aquatic product’s health efficacy, such as antioxidation, anti-cancer, cancer prevention and treatment of cardiovascular diseases and so on, to meet the people’s need for healthy products, in order to provide the theoretical guidance for the further development of the nutritive and sanitarian function of aquatic products and promote the complement of aquatic and terrestrial food resources for human health better.

Abstract:Psyllium husk powder (PHP) is a food hydrocolloid rich in both soluble and insoluble dietary fiber. Previous studies have shown that the interaction between polysaccharide hydrocolloids and proteins could affect the ability to form gels, which suggests that the addition of PHP to surimi paste may have an impact on the properties of surimi gels. In order to study the the development and application of PHP in surimi products, three factors including the amount of PHP added, gelation temperature and gelation time on the gel properties of surimi were investigated, using frozen silver carp (Hypophthalmichthys molitrix) surimi as the research object, gel strength and water holding capacity (WHC) as the inspection indicators. On the basis of single factor experiments, three-factor and three-level orthogonal experiment and verification experiment were carried out. The best processing conditions obtained through orthogonal test result were as follows: PHP addition amount 0.1%, gelation temperature 45 °C, and gelation time 2 h. The cooking loss rate, protein pattern and microstructure of fish sausage prepared by the traditional process (without PHP, gelation temperature 40 °C, gelation time 1 h), optimized process (0.1% PHP addition, gelation temperature 45 °C, gelation time 2 h) and optimized control process (without PHP, gelation temperature 45 °C, gelation time 2 h) were analyzed and compared to verify the properties of surimi gels under different conditions. The single factor test results showed that the addition of an appropriate amount of PHP (0.1%-0.3%) could increase the hardness and WHC of the surimi gel, but PHP might have an adverse effect on the deformation, and compared with the traditional technology, slightly higher temperature and longer time would help the surimi mixture to form better gel; the results of cooking loss rate, SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and scanning electron microscopy (SEM) in the verification experiment indicated that the participation of PHP might reduce the cooking loss of surimi gel formed at higher gelation temperature, promote cross-linking between myosin heavy chain molecules, retard protein degradation and help to form a denser gel structure. PHP as a new food raw material used in the development of high-quality and healthy surimi products was preliminarily explored in this study. And it is expected to be able to provide some reference for enriching the research content about application of hydrocolloid in the performance of surimi gel properties.

Abstract:China’s coastal commercial species of marine fish are both rich and varied. However, most of the catch is produced by the small-scale fisheries, and the small-scale landings are destined for local human consumption and sold as primary products. Economic benefit is constrained because lack of quality control concern. A construction of value chain based on freshness-locked products with upper limit quality instead of primary products is worth to explore. One of species, S. schlegelii was taken as case study. In order to change the existing sales mode of primary agricultural products of S. schlegelii through product design, the exploration was carried out from two aspects: the upper limit of quality and the effect of freshness-lock. Firstly, from the slaughter stress intensity, the limit quality of S. schlegelii was explored, including the upper limit of quality under the minimum stress and the lower limit of quality under fatigue death, compared with the quality status of commercial products. Then, through the management of quality determination period, the effect of freshness-locking on high end S. schlegelii was discussed. According to the degree of slaughter stress, healthy living animals were divided into three treatment groups: minimum stress-spinal cord destruction (SCD), low stress - spinal cord cutting (SCC) and high stress - suffocation in air (SA). The commercially available products were from supermarket (SM) and local fish market (FM), respectively. The measures of freshness-locking were to cool the fish to about 0 °C immediately after quick killing, and to refrigerate the fresh products at 2 °C. The characteristics of postmortem rigor of S. schlegelii were analyzed from rigor index, muscular contraction and breaking strength. The quality of muscle and its stability in cold storage were analyzed by whiteness value, pH value, ATP-related compounds and microstructure. The results showed that: ① Under the lowest stress, the maximum rigor of S. schlegelii reached 24 h after death and lasted for 24 h. In the high stress group, the rigor index reached 90% after 6 h and was free from rigor after 48 h. Muscular contraction is correlated with rigor index. Muscles under high stress showed no signs of contraction during storage, while those under low stress contracted rapidly before the occurrence of maximum rigor. During cold storage, muscle breaking strength showed a decreasing trend, but it was significantly delayed in the lowest stress group. ② Under the minimum stress, the initial ATP value was 2.83 μmol/g, and the minimum pH value was 6.58. Under low stress, ATP value was 0.94 μmol/g at 6 h after death, and the lowest pH was 6.56. Under high stress, ATP value was 0.50 μmol/g and the lowest pH was 6.54 at 6 h after death. ③ delayed effect, the whiteness of muscle fibers was gradually degraded and the space between muscle cells was expanded during cold storage, but the lowest stress group could effectively slow down the above trend. ④ quality status at the sales, the results of fresh product quality analysis of the supermarket group and the fish market group showed that the quality of the supermarket group was similar to that of the low stress group at 6 h after death, and the quality of the fish market group was similar to that of the high stress group at 120 h after death. To sum up, the commercially available primary agricultural products intermingle different levels of quality for S. schlegelii. The product design is applied through the treatment of freshness-locking, which not only effectively prolongs the shelf life of chilled fish, but also meets the needs of consumers for high quality.

Abstract:Fermentation is a food preservation method with a long history. Fermentation not only give a unique flavor and taste of sea food, but also improve the nutrition value dut to enzymes and microbial metabolic activities. Fermented aquatic products can not only give aquatic products unique flavor and taste, but also increase the nutritional value of aquatic products. With the development of high-throughput sequencing technology and the creation and improvement of genomic databases, metagenomic composition is an important tool for studying the microbial community structure of fermented aquatic foods, the interaction between microorganisms, and functional gene mining. Lactobacillus, Staphylococcus and Saccharomyses have a close relationship with the quality of fermentation aquatic products, and is commonly used as starter in the production of fermented aquatic products. This paper reviews the research method of microbial community in recent years and microbial community structure and success in the fermentation process, to explore the effects of microorganisms on the quality formation of traditional fermented aquatic products. The research direction of the relationship has been prospected in order to provide effective theoretical basis for quality consensus and industrial production in the fermentation water product industry.

Abstract:Calcium is an essential mineral for human body. Deficiency of calcium leads to osteoporosis, even induces diseases such as hypertension, diabetes and kidney stones. The common calcium supplements found on the market include calcium acetate, calcium lactate and calcium gluconate. Calcium concentrations of these calcium supplements are high, while bioavailability is low. It has been reported that the collagen peptide chelated calcium has the characteristics of high stability, strong anti-interference ability, and high bioavailability. In this study, fish collagen peptide and CaCl₂ were physically milled with a high-energy wet ball mill, in order to develop new production process of collagen peptide chelated calcium. The techniques including FT-IR infrared spectrum, X-diffraction and EDS energy spectrum, were used to analyze physicochemical properties and structure of the collagen peptide chelated calcium. As the milling time was extended from 15 to 240 min, the particle size of the mixture showed an approximately normal distribution and the average particle size of fish collagen peptides gradually decreased from 872 to 343 nm. The absolute value of ZETA potential gradually increased from 3 to 11 mV. The proportion of molecular weights in the <500 u range decreased from 55.806% to 35.999%, that in the 500-1 000 u range increased from 19.178% to 27.031%, that in the 1 000-3 000 u range increased from 21.672% to 30.539%, and that in the >3 000 u range increased from 4.344% to 5.981%. pH value gradually increased from 6.34 to 8.75. The calcium chelation rate gradually increased from 74.21% to 85.42%. The chemical structure of fish collagen peptide chelated calcium was similar to that of fish collagen peptide. However, -COO^-1 V_AS absorption peak (1 643.89 cm^-1) of collagen peptide moved to 1 540-1 555 cm^-1 (shorter wave number) after milling, and the characteristic absorption peak of -NH₂(3 313.9 cm^-1) shifted to 3 337.12-3 380.59 cm^-1 (longer wave number). The characteristic broad fish collagen absorption peak located at 2 θ=20° disappeared after milling, while multiple sharp peaks (including 2 θ=26, 28, 48 and 58°) and dispersion peaks appeared, indicating that it changed from amorphous to both crystalline and amorphous structure. The proportion of calcium in the collagen peptides chelated calcium gradually increased, confirming that more calcium was chelated by collagen peptides. The above results suggest that high-energy wet ball milling can be applied to produce fish collagen peptide chelated calcium, which has the advantages of simple processing, no pollution, and high chelation rate.

Abstract:Engraulis japonicus is a small-sized economic fish with high nutritional value, which is widely distributed in Western Pacific and Western Indian Ocean. Fresh E. japonicus is highly perishable products due to their high activity of endogenous enzymes. Therefore, dried E. japonicus is processed directly after fishing and then sold after transportation and circulation. The storage stability of dried E. japonicus can be improved by selecting appropriate packaging methods, such as air packaging, vacuum packaging, CO₂ packaging, and modified atmosphere packaging. After packaging, dried E. japonicus and other aquatic products can avoid secondary pollution, and slow down the degradation rate of product quality. In order to investigate the effects of different packaging on the quality characteristics of dried E. japonicus during storage at normal temperature, air packaging was compared with vacuum packaging, modified atmosphere packaging and CO₂ packaging, the total bacterial count, TVB-N, POV, TBA, color difference, volatile flavor components and sensory score were determined and analyzed. The results showed that VP, MAP, and CP can effectively inhibit microbial growth. After 8 days storage at 25 °C, TVB-N, POV and TBA values of VP group were 47.08%, 4.13% and 25.49% lower than those of AP group. The VP group had better effects in slowing down the color change of samples, protecting the structural integrity of muscle fiber, retaining volatile flavor components, and maintaining sensory properties, which confirmed that vacuum packaging is the best choice. The shelf life prediction model of dried E. japonicus was established based on the Arrhenius equation, and the shelf-life of vacuum-packed dried E. japonicus was 6.07 d and 3.23 d at 25 and 35 °C. The study can provide a theoretical basis for the quality control of dried E. japonicus in the process of normal temperature transportation.

Abstract:This paper reviews the biological hazards of traditional processing method of raw ready-to-eat aquatic products and the effects of seven non-thermal sterilization techniques on microbial inactivation in raw ready-to-eat aquatic products and their quality, to provide useful information for the application of non-thermal sterilization techniques in the processing of raw ready-to-eat aquatic products. Ultra-high pressure treatment, irradiation and DPCD technology have good sterilization effect, but their influence on the quality of aquatic products is different due to the different kinds of aquatic products, process parameters and other conditions. Ultra-high pressure treatment and DPCD technology will reduce the transparency and increase the hardness of fish and shrimp under high treatment intensity, and irradiation will generate peculiar smell of aquatic products under high treatment intensity. stable chlorine dioxide, ozone, acid electrolyzed water and biological preservatives have good antibacterial and bacteriostatic effects and little impact on the quality of aquatic products, so they can be used to extend shelf life and maintain quality.

Abstract:In recent years, there have been many studies on the processing and preservation of shrimp by Ultra-High Pressure (UHP) technology, but few study reports on the degradation of ATP and the accumulation of its related products during UHP chilled storage. In order to explore the influence of ultra-high pressure treatment on the changes of ATP related compounds in Litopenaeus vannamei during chilled storage, different pressure conditions (0, 100, 200, 400 MPa) were used to store L.vannamei at (4±1)°C after treatment. The results showed that the main compounds were ATP and ADP, and the contents were 8.10 μmol/g and 2.11 μmol/g respectively, accounting for 73.51% and 19.14% of the total ATP-related compounds in L.vannamei. After being treated at 100 and 200 MPa, the contents of ATP and ADP in shrimp meat decreased rapidly, while the content of AMP increased significantly. The contents of ATP and ADP were higher after 400 MPa treatment, then decreased rapidly after 1 day storage. During storage, AMP, IMP and HxR of all treatment groups showed a trend of first increase and then decrease, while Hx and AdR basically showed a linear trend of increase, also Ad was not detected in all treatment groups. The degradation of ATP-related compounds in the 400 MPa treatment group was the slowest. The study indicated that ultra-high pressure(UHP) treatment had no effect on the ATP degradation pathway in L.vannamei, but it affected the degradation rate of ATP-related compounds. This study provides some theoretical basis for keeping shrimp fresh by using ultra-high pressure technology and ensuring shrimp favor and quality to the maximum extent.

Abstract:Trachinotus ovatus is a marine commercial fish because of high nutritional value and special flavour, which is widely cultured in Guangdong, Fujian and other southern coastal areas in China. In recent years, as the production of T. ovatus increases, T. ovatus in the domestic market is mainly sold live or chilled, causing many problems such as short shelf life, low economic benefits and so on. Salting is one of traditional ways to preserve or to process fish. Salting is based on the penetration of salt into the fish muscles as a direct consequence of its ability not only to reduce water activity of fish muscles and inhibit the growth of microorganisms, but also improve the quality and flavour of the product. Because T. ovatus has no muscle spines, it is suitable to extend the shelf life of products and improve the added value of products by salting, air drying and other techniques. Traditional curing methods include dry salting, wet salting and mixed-salting and they have some shortcomings such as slow curing speed and uneven curing. With the development of technology, ultrasonic assisted curing and ultra-high pressure assisted curing have been developed, which has the advantages of fast curing speed and good product quality. At present, there are few reports on the comparison between the new curing methods and the traditional curing methods. In order to explore the effects of dry salting, wet salting and ultrasonic assisted curing on the physicochemical parameters and volatile flavor components of T. ovatus, the basic nutritional components, salt content, pH, thiobarbituric acid (TBA) value, fatty acid composition and volatile flavor compounds of salted fish were determined and analyzed. The results showed that after different curing processes the protein and fat content of T. ovatus increased, but the moisture content of T. ovatus decreased. The moisture contents of dry salted, wet salted and ultrasonic assisted salted fish were 53.71% ± 0.97%, 61.45% ± 0.72%, 59.29%±1.41%, respectively. Compared with fresh T. ovatus, the salt content of dry salted, ultrasonic assisted salted and wet salted fish increased, which were (3.29 ± 0.15), (2.64 ± 0.02) and (2.15 ± 0.11) g/100 g, respectively. However, the pH value of T. ovatus decreased after different curing processes. After curing processing, the lipids of fish meat underwent oxidation reaction, the TBA value increased. The TBA values of dry salted, wet salted and ultrasonic assisted cured fish were (0.80±0.07)、(0.55±0.09) and (0.73±0.08) mg MDA/kg. The fatty acid composition changed after curing processes with increase of saturated fatty acids and monounsaturated fatty acids and decrease of poly-unsaturated fatty acids. In this study, 54, 56, 62 and 57 volatile flavor compounds were detected from T. ovatus, dry salted, wet salted and ultrasonic assisted salted fish respectively. The volatile flavor compounds were mainly aldehydes, alcohols and ketones, which played an important role in flavor formation. The results showed that compared with the other two methods, the water content of dry salted fish was the lowest, but both the salt content and TBA value was the highest. The relative content of aldehydes and alcohols in the volatile flavor compounds of fish cured by ultrasonic assisted was the highest, and the pH value was the lowest. This study can provide technical and theoretical reference for curing processing and production process optimization.

Abstract:Shrimp meal is one of the most important processed products of Antarctic krill (Euphausia superba). During processing, heat treatment will cause the loss of nutrients and the destruction of active substances, which is the most important factor that determines the quality of shrimp meal. In order to grasp the changes and flow paths of the main substances during the processing of shrimp meal, by measuring the changes in the content of main nutrients such as moisture, ash, protein, lipid and the loss of functional components such as fatty acids and astaxanthin in the two key processes involving heat treatment, cooking and drying, the flow path and reasons for changes of each main substance were analyzed. The results showed that 8.49% of water was lost during the cooking process, and 63.5% of the water was lost during the drying process, mostly in the form of evaporation; the protein lost 1.12% during the cooking process, of which 0.87% flowed to the cooking liquid, and the loss was mainly water-soluble protein. The loss of 6.05% during the drying process; the lipids were reduced by 1.11% and 1.61% during the cooking and drying processes. Further analysis of the fatty acid composition revealed that the content of polyunsaturated fatty acids decreased from 45.57% to 43.65%. The relative content of EPA is reduced by 0.41% and 1.16% respectively during the drying process. The relative content of DHA does not change much during the cooking process, but is reduced by 0.68% during the drying process. Astaxanthin is a heat sensitive substance, which was affected by heat treatment and reduced by 29.4 and 58.6 mg/kg during the cooking and drying processes. The ash content was reduced by 2.85% and 0.85% during the cooking and drying process respectively; the results showed that the main substances lost during the cooking process were the soluble substances in the cooking liquor and a small part of the heat-sensitive substances, and the drying process mainly caused moisture evaporation and destruction of heat-sensitive substances such as astaxanthin. The study initially grasped the content changes and flow paths of the main substances during the processing of E. superba shrimp meal, analyzed the reasons for the changes and the main influencing factors, and discussed and proposed a plan to reduce the material loss, which can be used for the subsequent processing of Antarctic krill meal. The optimization of parameters provide a theoretical basis, which is of great significance for improving the quality of shrimp meal and promoting the high-quality utilization of E. superba resources.

Abstract:With the promotion of global salt reduction, people's health needs for low salt diet are increasing in recent years. Low sodium salt food with good flavor and appearance has become one of the research hotspots. In order to adapt to the needs of consumers for healthy diet, the present research made dried salted products using sodium citrate as a salt substitute and investigated the quality of the products. The dried salted products were made from red tilefish by air drying after soaking with 9% (W/V) salt (control group) and sodium citrate (experimental group). The quality of the products was indicated by the color and the pH of skin, Na⁺ concentration, texture, flavor characteristic substance IMP, and freshness index K value of meat, and sensory analysis after baking. In the experimental group, a*, C* and pH of the skin of dried salted fillet samples were significantly higher than those of the control group; the Na⁺ concentration in meat was 39% of that of the control group, which had higher water holding capacity, lower breaking load and breaking stress, and its breaking deformation was significantly higher than that of the control group; at the same time, there was no significant difference in IMP concentration as umami indexes and K value as fresh index. The sensory analysis results of the experimental group showed significantly lower saltiness score than the control group. On the basis of slightly higher appearance score, there was no significant difference in chewing, umami and overall acceptability. Using sodium citrate instead of salt to make dried salted products of red filefish fillets can effectively improve the skin color and reduce Na⁺ concentration while ensuring the quality parameters. Sodium citrate may be one of the ideal sodium salt substitutes, which can provide new ideas for improving the process, adjusting the taste, and reducing the amount of sodium salt of dried salted aquatic products.

Abstract:Solenocera crassicornis, also known as red shrimp, is one of the main marine aquatic products of China. It is much-loved by consumers and producers for its good flavor and rich nutrition. Currently, many types of shrimp are sold in the market, such as fresh shrimp, frozen shrimp, dry shrimp or shrimp surimi products, etc. Surimi is a kind of thermally gelated food that was widely accepted by the public because it is rich in protein and low in fat, and is valued for its unique gelling properties. However, due to the physiological and biochemical characteristics of red shrimp meat, it is difficult to form competitive advantage because of poor gel forming and unstable quality, which greatly restricts the development of shrimp surimi products. It is very important to improve the gel properties of shrimp surimi. Compared to the native starch, modified starch usually has better gelatinization performance and be used as additives to significantly improve the performance of the gel. Hydroxypropyl distarch phosphate (HPDSP) is a modified starch which has attracted much attention for its good filling effect, stable gelation properties and low cost in food industry. In order to investigate the effect of HPDSP on improving the gel properties of S. crassicornis shrimi gel, 1%, 3%, 5%, 7% and 9% addition of HPDSP were respectively added to the shrimp surimi. Using the gel strength, texture profile analysis, water holding capacity (WHC), gel microstructure as the indicators, and combined with the analysis of the secondary structure of myofibril protein from shrimp surimi sol, gelatinized shrimp surimi and surimi gel by circular dichroism spectrum, the effects of HPDSP on the gel performance of shrimp surimi and its mechanism were explored. The results showed that HPDSP can increase the gel strength and WHC of shrimp surimi gel, and reached the maximum value when the addition amount was 7%. Furthermore, HPDSP reduced the a* value and b* value of the shrimp surimi gel, but the L* value and whiteness did not change significantly except for the 9% additive group. An appropriate amount of HPDSP could improve the hardness, springiness, cohesiveness and chewiness, and promote the formation of a denser and stabler gel network structure of the shrimp surimi, which was consistent with the gel strength and WHC. In addition, during the gelatinization of shrimp surimi, heating increased the contents of β-sheet and random coil, but decreased the content of α-helix in myofibrillar protein. At the same time, HPDSP affected the thermal denaturation and aggregation of myofibril protein, thereby changing its secondary structure and affecting the formation of shrimp surimi gel. Overall, adding 7% of HPDSP could significantly enhance the gel properties of shrimp surimil. The results of this study would contribute to the utilization of HPDSP for the functionality of surimi products improvement.

Abstract:snakehead fish (Channa argus), a carnivorous fish, is widely distributed in freshwater areas of Asia. C. argus has fatty meat, few intermuscular bones, and is rich in protein and essential amino acids. It has the advantages of delicious taste, and rich nutrition, and is favored by consumers. At present, the common raw C. argus processed products on the market–freshly prepared snakehead fish fillets are seasoned with salt, monosodium glutamate, spices and so on. In order to respond to the national salt reduction policy and promote the development and application of new seasonings, this article uses yeast extract to season fresh C. argus fillets. In order to investigate the effects of adding different yeast extracts on the flavor and texture of raw fish fillets, the volatile components were extracted by simultaneous distillation extraction (SDE) from seasoned snakehead fish fillets, and the flavor and composition of six groups of seasoned C. argus fillets (control check CK group, FA02 group, KU012 group, FG10 group, FA39 group, F55 group) were analyzed by GC-MS in combination with electronic nose and electronic tongue. The quality of the six groups of seasoned snakehead fish fillets was further evaluated by combining sensory, color and texture analysis. The results showed that 42 volatile substances were detected in the CK group, while five yeast extracts were added (FA02, KU012, FG10, FA39, F55) with significantly more volatile substances of 60, 66, 56, 52 and 46 kinds respectively. The main characteristic volatile substances in the fillets were aldehydes, such as heptanal, decanal and (E, E)-2,4-decadienal and so on; after adding different types of yeast extracts, the volatile substances in each group of fish fillets increased, such as (E)-4-decenal, 2-nonanone, 3-nonen-2-one and so on. The KU012 group showed the greatest increase in the types and content of volatile substances, such as (E)-2-pentenal with fresh odor, (E, Z)-2, 6-nonadienal with cucumber flavor, and (Z)-2-(2-pentenyl)furan to enhance the overall flavor. The results by electronic nose and electronic tongue showed significant differences in odor and taste between each yeast extract group and the CK group. Compared to the CK group, the C. argus fillets seasoned with the addition of yeast extract had a light yellow color, slightly reduced texture and higher sensory scores. Different types of yeast extracts could improve the flavor, texture and sensory quality of C. argus fillets to a certain extent, and the KU012 group had the best overall performance. This study provides reference for the application of yeast extracts in the seasoning of aquatic products.

Abstract:Sea cucumber intestinal peptide has antioxidant, anti-cancer and anti-fatigue effects, while the strong fishy smell restricts its application in food industry. In this study, watermelon essence was entrapped into V-type crystalline starch using solid encapsulation method. The inclusion complex (IC) was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Meanwhile, the IC was added to sea cucumber intestinal peptide, and the flavor of mixed samples stored at different temperatures (4, 25, 50 °C) were investigated. The results showed that the natural watermelon flavor was introduced into V-type crystalline starch, and the encapsulation rate of IC was 63.8% (W/W). Compared with V-type crystalline starch, the crystallinity of IC decreased from 39.5% to 28.9%, and the enthalpy value was 13.0 J/g. The intensities of peak at 1 023 and 1 158 cm⁻¹ were significantly lower than those of V-type crystalline starch, and the characteristic peak of C-H bending vibration at 856 moved to 839 cm⁻¹. The electronic nose and sensory analysis showed that the watermelon flavor stored at different temperatures exhibited controlled release characteristics. The IC could mask the odor of sea cucumber peptide and give samples a fruity flavor, thereby enhancing the acceptability of consumers. In conclusion, natural watermelon flavor has been successfully encapsulated in V-type crystalline starch, and can effectively improve the flavor of intestinal peptides and prolong the flavor retention time of the essence. These results will enrich and develop the flavor quality improvement theory of aquatic products, and provide the theoretical reference for high-value application of aquatic products.