Program

Commercial gelatin production was extracted from bovine and porcine, but fish skin was not for commercial production because of fishy odor. Tilapia production is growing worldwide and to better utilize wastes from the processing industry, one important is production of high quality fish gelatin to meet the need of markets that made value for Tilapia skin being material for commercial gelatin production. Fish skin was used for only laboratory gelatin extraction because of fishy odor in tilapia skin. The objective of this research was to remove fishy odor from Tilapia Skin using for gelatin extraction. tilapia (Oreochromis niloticus) skin was treated with 3 treatments; alkaline-acid (NaOH-citric acid-sulfuric acid), NaCl and NaCl and alkaline-acid treatment at room temperature. Then the skin was washed until washing water was neutral. The gelatin was extracted by hot water at 50 °C for 3 h then gelatin were evaporated by rotary evaporator at 50 °C for 3 h and dried by hot-air oven at 50 °C for 24 h. The gelatin yield, gel strength, quality and quantity of volatile compounds were analyzed by using GC-MS and sensory evaluation analysis. The best treatment was NaCl and alkaline-acid treatment that shown high yield, high gel strength and was accepted by the panelists in the appearance, color, and fishy odor. NaCl and alkaline-acid treatment get rid of fishy odor from tilapia skin that made value for tilapia skin being material for commercial gelatin production.

Stinky mandarin fish is a spontaneously fermented fish products in China and is famous for its unique smell and special texture. It was mainly produced in family workshop, therefore, little is known about the fermentation process. In this study, we firstly optimized the fermentation parameters, and then metagenomics approach was applied to explore the dynamic of microbiota during the fermentation, finally changes of flavor compounds were measured by both E-nose and HS-SPME-GC-MS. With an orthogonal design method, we obtained the optimized fermentation parameter of 12 °C, 6 % NaCl and 7 days for fermentation. Metagenomic analysis showed that, at the early stage of fermentation, Vibrio, Photobacterium and Shewanella increased firstly and then decreased at the fourth day. It was supposed that these microbes might play important roles in the early stage of fermentation. Oceanisphaera, Psychrilyobacter, Fusobacterium and Arcobacter were increased since the fourth day, therefore, they may be functional at the later stage of fermentation. UniFraction UPGMA cluster analysis also showed that the fourth day’s microbial communities were different from others. GC-MS results correlated well with that of E-nose, in which ketones, aromatic, alcohols, nitrogen-containing, sulfur-containing and hydrocarbons showed an increasing trend in fermentation process. Especially, the alcohols, ketones, acids, nitrogen-containing, aromatic compounds and hydrocarbons changed drastically at the fourth day. In all, both metagenomic analysis and GC-MS results inferred that the fourth day was the key changing moment of fermentation. This study contributes to the rational cognition and regulation of the fermentation process of mandarin fish, and will promote the standardization of its production.

In order to study the temperature fluctuation on the quality and microbial diversity of large yellow croaker (Pseudosciaena crocea) with ice during logistic process. Cold chain and broken-off cold chain of large yellow croaker with ice were simulated in the period of logistic process, the real-time temperature of different circulation methods were monitored respectively by multi-point temperature acquisition instrument. Sensory evaluation, total viable counts (TVC) and psychrophilic bacteria counts (PBC) were evaluated for its quality and microbial number of large yellow croaker with ice during circulation. The microorganism changes of samples in different circulation were analyzed by PCR-DGGE fingerprint technology. The results showed that the deterioration of samples can be accelerated for temperature fluctuation and circulation time was positively correlated with sensory score and microbial number. Samples in cold chain and broken-off cold chain reached the end of shelf-life at 347 h and 275 h, TVC were 6.93±0.03lgCFU/g and 6.50±0.07lgCFU/g respectively. The result of PCR-DGGE demonstrated that the number of Staphylococcus saprophyticus and Pseudomonas fluorescens were increased gradually in later circulation, but the number of Vibrio Parahemolyticus was decreased. Pseudomonas sp., Psychrobacter sp., Pseudoalteromonas sp. and Shewanella sp. were dominant in cold chain circulation, and Pseudomonas sp., Psychrobacter sp., Shewanella sp. were the predominant bacteria in broken-off cold chain circulation. Therefore, Pseudomonas sp., Psychrobacter sp. and Shewanella sp. were the special spoilage organism of large yellow croaker in cold-chain and broken-off cold chain process.

Key words：Pseudosciaena crocea; Ice storage; Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE); Logistic process; Temperature fluctuation; Microorganism change

Tuna is one of the most valuable fish for production “Sashimi” and “Sushi” in Japan. The color of tuna meat, which is one of the most important quality factors, deteriorates due to the formation of metmyoglobin (metMb) caused by autoxidization during frozen storage. Additionally, the texture of meat deteriorates due to frozen denaturation of myofibrillar protein. Recently, ATP, the most important initial freshness indicator of fish meat, has been shown to suppress the formation of metMb, and frozen denaturation of myofibrillar protein. However, the initial freshness of frozen tuna meat can differ significantly, because tuna may be either alive or dead when the catch is landed. Therefore, it has been suggested that the initial freshness of tuna meat affects the quality changes during frozen storage. Accordingly, in this study we aimed to elucidate the relationships between the initial freshness of frozen tuna meat, quality changes during frozen storage, and frozen storage temperature.
We used frozen bigeye tuna, for which the initial freshness (pH and ATP content) had been determined. The frozen meat was sliced, packed in a plastic bag and maintained at -20, -35, -40, -45, or -60°C for 14 months. We measured the metMb ratio and Ca²⁺-ATPase activity during frozen storage.
The increase in the ratio of metMb in the high-freshness meat was lower than that in low-freshness meat at -40 to -20°C. The decrease in the ratio of myofibrillar Ca²⁺-ATPase activity of the high-freshness meat was higher than that of the low-freshness meat. However, no obvious difference was found in the changes of these indices at temperatures below -45°C, irrespective of the initial freshness of the tuna meat. Therefore, we suggest that the initial freshness of tuna meat affects quality changes during frozen storage, and that these changes can be suppressed at temperatures lower than -45°C.

【Background and Purpose】Lightly salted fish products have become increasingly popular. Because these products have high water content and low salt content, they need to be kept in frozen storage to have a long shelf-life. Unfortunately, little information is available on the quality changes of salted fish meat during frozen storage. The water holding capacity, color, and texture are decisive quality attributes for the consumer purchasing decisions. Therefore, the purpose of this study was to clarify the effect of salting and frozen storage on the quality changes of tuna meat.
【Material and Methods】Frozen bigeye tuna meat was thawed and cut into slices (3 cm×2 cm×0.5 cm). After soaking in different concentrations of NaCl solution, the samples were stored at -20°C for 1 w. The quality of the meat was evaluated by product yield, thawing loss, centrifuging loss, color characteristics, and texture profile.
【Results】The highest yield was obtained in 0.5 M and 1 M salted samples after both salting and frozen storage. The centrifuging loss decreased in 1 M or higher solutions salted samples after salting, but increased in the 2 M and 3 M salted samples after storage. After salting with 0.5 M or higher solutions, the samples became glossy and the hug angle of 1 M salted samples was the lowest and the most stable after frozen storage. The springiness, adhesiveness, and cohesiveness increased after salting with 0.5 M or higher solutions, indicating that salted fish products have a characteristic mouthfeel and texture.

Myoglobin (Mb) is an oxygen-binding heme protein. There are three forms in Mb, deoxyMb, oxyMb and metMb. In living organisms, two ferrous (Fe2+) forms of deoxyMb and oxyMb are the most common forms. However, in postmortem organisms, oxyMb is slowly converted to metMb as the oxidizing ferrous heme to ferric (Fe3+) heme and bound O2 molecule is released. The reaction is known as an autoxidation of oxyMb. Since metMb is stable form and its color tone shows brown, the autoxidation of oxyMb to metMb induces discoloration of muscle from red to brown. Mechanisms of the autoxidation of oxyMb to metMb and of the reducing system of metMb have been studied in vitro model, however, regulation system for autoxidation of oxyMb in situ hasn't investigated. We interested in a behavior of Mb in fish muscle, and demonstrated that the autoxidation of oxyMb was suppressed by ATP containing in muscle. In this study, we investigated an effect of ATP in frozen muscle on the autoxidation rate of oxyMb in thawed muscle.
Yellowtail Seriola quinqeradiata of average body weight 5.0 kg were used. After instantly killed, the round fish were cooled in iced sea water for various periods to prepare fillets containing various ATP contents. These samples were frozen at -35 degree, then the cryopreserved sample was thawed in iced water. After preservation, color tone of the sample was checked and the autoxidation rate of Mb was measured by spectrum analysis of extracted Mb from thawed sample. After thaw of cryopreserved sample, air-exposing accelerated the autoxidation. Moreover, the autoxidation rate of purified Mb prepared from fillet containing high concentration of ATP was slower than it of Mb from fillet containing low concentration of ATP. We speculate that a conformational change in Mb occurred in cryopreservation/thaw of muscle and it was suppressed by ATP.

Surimi-based products such as kamaboko tend to deteriorate upon freezing. In our previous study, we found both positive and negative effects of addition of various kinds of starch on quality changes of surimi gels upon freezing. In the present study, starches with different grain sizes were prepared, and their effects were determined on the changes in the quality of surimi gels after freezing.
Frozen surimi was thawed and chopped with NaCl and starch, including potato starch and wheat starch with a normal or micro grain size, then heated at 90 °C for 30 min and frozen by quick or slow freezing. After 1 week of frozen storage at -20 °C, the water-holding capacity (WHC), microscopic observation, physical properties by puncture test and texture profile analysis (TPA) were determined.
For WHC, there was no significant difference between surimi gels with the two sizes of starch grains before freezing. After freezing, surimi gels with large-size grain starch showed a higher drip loss, especially in the case of slow freezing. The results of microscopic observations corresponded to those of WHC. Regarding the breaking strength, there was no significant difference between surimi gels containing two types of potato starch. However, surimi gels containing wheat starch with a micro grain size showed a significantly lower breaking strength than those containing normal grain size, both before and after freezing. The hardness, determined by texture profile analysis, showed the same tendency as the breaking strength. It was considered that the physical changes were related to different retrogradation degrees of potato starch and wheat starch.
Above results revealed that the changes in the quality of starch-containing surimi gels, were affected not only by freezing conditions but also by starch properties such as the grain size, retrogradation, and structural destruction.

In spite of the widespread use of microbial transglutaminase (MTG) as an additive to improve the texture of surimi seafood, little information is available regarding the optimization of the effect. The objective of the study was to elucidate the effective use of MTG to improve the textural properties of two-step heated gel prepared from walleye pollack surimi in terms of preheating time, protein concentration and the enzyme content. Changes in preheating time as well as the protein concentration of salted surimi paste caused considerable variation in the effects of MTG on textural properties of two-step heated gel. The maximum enhancing effect of MTG for the breaking force was obtained when salted surimi paste with 80 mg/g of protein concentration was preheated at 25 ºC for 1-2 h. On the other hand, irrespective of the protein concentrations, the penetration distance of two-step heated gel declined with preheating time upon addition of MTG, resulting in the formation of harder but less elastic gel with larger gel stiffness. Decrease in MTG content in addition to shorting of preheating time of salted-ground surimi with 80 mg/g of protein concentration was effective to prevent the decrease in the elasticity of two-step heated gel. Upon addition of MTG, cross-linking reaction of myosin heavy chain (HC) was extensively promoted with the insolubilization into 8 M urea- 2% SDS- 2% 2-mercaptoethanol, suggesting the formation of the huge HC polymer. The elasticity of two-step heated gel declined with accumulation of huge HC polymer by MTG. In addition, in spite of the similar extent of the progress of the cross-linking reaction of HC, textural properties of two-step heated gel were different by the conditions, indicating that control of non-covalent interaction between myofibrillar proteins as well as cross-linking reactions of HC was critical to maximize the effects of MTG.

Japanese scallop (Patinopecten yessoensis) is one of commercially valuable bivalve mainly aquacultured in Hokkaido and Tohoku area of Japan and Dalian of China. It is not only consumed as Sashimi, but also processed into boiled-frozen and dried adductors. There were some studies about the thermal gelation of salted paste from scallop striated adductor muscle was similar as commercial surimi-based products.
Usually surimi based products were processed by 2-2.5% salted surimi which is manufactured by applying a simple technology of washing minced meat, dehydrating and mixing with cryoprotectants. In the present study, we tried to develop a completely new gel-type food without washing process to preserve the favored scallop taste and flavor at low salt concentration. Live cultured scallops with a shell width of 12–14 cm were used. The adductor muscles including striated and smooth muscle were dissected. The adductor muscle was homogenized with different condition by changing the ionic strength (0-0.1), water content, and blending speed. And then it was stuffed into Polyvinyl chloride casing tubes (22 mm in diameter and 70 mm in length). The cooked gel by boiling with or without preheating was evaluated for folding test and gel strength assessment. It was found that the gelation was related to the freshness and the particle size of minced meat at low ionic strength condition. With higher ATP content and more homogenous tiny particle size of minced meat, it could form more elastic gel.
The mechanism of gelation at low ionic strength condition was further studied by considering the changes of myosin solubility, ATP content with freshness decrease, myosin ATPase activity, transglutaminase activity and SDS-PAGE and Scanning Electron Microscope analysis.

The aim of this study was to determine the effect of antioxidant and antibacterial of liquid smoke nanocapsules on catfish (Pangasius sp.). The liquid smoke combination (corn cob and coconut shell) was processed into nanocapsule with 1/6 gum arabic + 4/6 maltodextrin + 1/6 alginate as coating materials had the total phenol, carbonyl, and RSA of 3.682%; 3.439%; and 91.348%, respectively. Liquid smoke nanocapsules were applied to the patin fish fillet and stored at room and cold temperature. Observations were made on days 0, 2, 4, 6, 8, and 10 of peroxide value, Thiobarbituric acid, and Total plate count. The results showed that liquid smoke nanocapsules effectively inhibit the oxidation of patin fish fillet for the storage on the fourth day, with the value of PV 4.625 and 3.347 ml eq / kg and TBA 3.206 and 2.802 mg / kg for each temperature. The results also showed that liquid smoke nanocapsules were able to inhibit microbial growth indicated by the TPC value until the tenth day below SNI (1x105 colonies / g) at all storage temperatures.

Keywords: Catfish fillet, liquid smoke nanocapsules, antioxidant, antibacterial

Citrus essential oil loaded chitosan based microcapsules (chitosan-citrus microcapsules) were prepared and applied in chilled Pacific white shrimp (Penaeus vannamei). Microcapsules were prepared by emulsion-ionic gelation technique using 6 different emulsifiers, and their embedding and release rate as well as particle size were analyzed to optimize the emulsifier. It was shown that emulsifier type had significantly effect on the size and shape of microcapsules. The microcapsules has the highest embedding rate of 68.1% and minimum particle size of 289.3nm with Tween 60 as the emulsifier, thus their structure and thermal behavior were further analyzed using FT-IR and DSC, respectively. Results indicated that citrus is successfully embedded in the chitosan-based microcapsules. Then the microcapsules were applied in the preservation of Pacific white shrimp during superchilled storage (-3℃). Physicochemical (drop loss, total volatile basic nitrogen, K value and thiobarbituric acid-reactive substances) and microbiological (total viable count) properties of the shrimp coating with chitosan-citrus microcapsules being preserved under -3℃ were periodically evaluated. The total volatile basic nitrogen (TVB- N) of the samples treated with chitosan-citrus microcapsules was merely 26.81 mg/100g by the 12th day, much lower than that of the control of 45.93 mg/100g. The total viable count (TVC) of the sample treated with chitosan-citrus composite and the control were 5.1 log(CFU/g) and 6.3 log(CFU/g), respectively, indicating the effect of chitosan-citrus microcapsules on the inhibition of microbial growth, suggesting that microcapsules could reduce the spoilage of Pacific white shrimp significantly. The chitosan-citrus microcapsules would be a promising biological material for the preservation of aquatic products during chilled storage.

A simple, green method of synthesizing silver nanoparticles (AgNPs) with ultrasonic treatment was developed using sodium alginate and ascorbic acid as stabilizing agent and reducing agent, respectively. A possible mechanism involved in the reduction and stabilization of nanoparticles was studied. The effect of reaction conditions such as pH, the concentration of AgNO3 and ascorbic acid, ultrasonic temperature, ultrasonic time and ultrasonic power on the synthesis of silver nanoparticle was investigated. The silver nanoparticles were characterized by UV-vis spectroscopy, fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Antibacterial activity of the silver nanoparticles was evaluated by minimal inhibitory concentration (MIC) and zone of inhibition (ZOI) on two kinds of Gram bacteria. The results indicated the formation of spherical, nanometer-sized, face-centered cubic particles of AgNPs. The formation rate, size and distribution of the silver nanoparticles were significantly affected by the reaction parameters. Compared to the control, the synthesized silver nanoparticles had significant antibacterial activity. The MIC (11.60 mg/mL) against Gram positive bacterial strains [Staphylococcus aureus (KCTC1928)] was the same as that against Gram negative bacterial strains [Escherischia coli O157:H7 (ATCC25922)]. The ZOI (12.58 mm±0. 22 mm) against the former bacteria was very close to that (12.75 mm± 0. 15 mm) against the latter. The synthesized silver nanoparticles served as a great preservation material thus possessing broad prospects in the preservation of fishery products to extend the shelf life.