Changes in the microbiological and physicochemical quality of high-pressure-treated oysters (Crassostrea gigas) during chilled storage

An Intelligent Method for Predicting Pacific Oyster (Crassostrea gigas) Freshness Using Deep Learning Fused with Malondialdehyde and Total Sulfhydryl Groups Information

To achieve a non-destructive and rapid detection of oyster freshness, an intelligent method using deep learning fused with malondialdehyde (MDA) and total sulfhydryl groups (SH) information was proposed. In this study, an "MDA-SH-storage days" polynomial fitting model and oyster meat image dataset were first built. AleNet-MDA and AlxNet-SH classification models were then constructed to automatically identify and classify four levels of oyster meat images with overall accuracies of 92.72% and 94.06%, respectively. Next, the outputs of the two models were used as the inputs to "MDA-SH-storage days" model, which ultimately succeeded in predicting the corresponding MDA content, SH content and storage day for an oyster image within 0.03 ms. Furthermore, the interpretability of the two models for oyster meat image were also investigated by feature visualization and strongest activations techniques. Thus, this study brings new thoughts on oyster freshness prediction from the perspective of computer vision and artificial intelligence.

Physicochemical and structural changes of myofibrillar proteins in muscle foods during thawing: Occurrence, consequences, evidence, and implications

Myofibrillar protein (MP) endows muscle foods with texture and important functional properties, such as water-holding capacity (WHC) and emulsifying and gel-forming abilities. However, thawing deteriorates the physicochemical and structural properties of MPs, significantly affecting the WHC, texture, flavor, and nutritional value of muscle foods. Thawing-induced physicochemical and structural changes in MPs need further investigation and consideration in the scientific development of muscle foods. In this study, we reviewed the literature for the thawing effects on the physicochemical and structural characters of MPs to identify potential associations between MPs and the quality of muscle-based foods. Physicochemical and structural changes of MPs in muscle foods occur because of physical changes during thawing and microenvironmental changes, including heat transfer and phase transformation, moisture activation and migration, microbial activation, and alterations in pH and ionic strength. These changes are not only essential inducements for changes in spatial conformation, surface hydrophobicity, solubility, Ca2+ -ATPase activity, intermolecular interaction, gel properties, and emulsifying properties of MPs but also factors causing MP oxidation, characterized by thiols, carbonyl compounds, free amino groups, dityrosine content, cross-linking, and MP aggregates. Additionally, the WHC, texture, flavor, and nutritional value of muscle foods are closely related to MPs. This review encourages additional work to explore the potential of tempering techniques, as well as the synergistic effects of traditional and innovative thawing technologies, in reducing the oxidation and denaturation of MPs and maintaining the quality of muscle foods.

Using OPLS-DA to Fingerprint Key Free Amino and Fatty Acids in Understanding the Influence of High Pressure Processing in New Zealand Clams

This study investigated the effect of high pressure processing (HPP) on the fatty acids and amino acids content in New Zealand Diamond Shell (Spisula aequilatera), Storm Shell (Mactra murchisoni), and Tua Tua (Paphies donacina) clams. The clam samples were subjected to HPP with varying levels of pressure (100, 200, 300, 400, 500, and 600 MPa) and holding times (5 and 600 s) at 20 °C. Partial Least Squares Discriminant Analysis (PLS-DA) and Orthogonal Partial Least Squares Discriminant Analysis (OPLS-DA) were deployed to fingerprint the discriminating amino and fatty acids post-HPP processing while considering their inherent biological variation. Aspartic acid (ASP), isoleucine (ILE), leucine (LEU), lysine (LYS), methionine (MET), serine (SER), threonine (THR), and valine (VAL) were identified as discriminating amino acids, while C18:0, C22:1n9, C24:0, and C25:5n3 were identified as discriminating fatty acids. These amino and fatty acids were then subjected to mixed model ANOVA. Mixed model ANOVA was employed to investigate the influence of HPP pressure and holding times on amino acids and fatty acids in New Zealand clams. A significant effect of pressure levels was reported for all three clam species for both amino and fatty acids composition. Additionally, holding time was a significant factor that mainly influenced amino acid content. butnot fatty acids, suggesting that hydrostatic pressure hardly causes hydrolysis of triglycerides. This study demonstrates the applicability of OPLS-DA in identifying the key discriminating chemical components prior to traditional ANOVA analysis. Results from this research indicate that lower pressure and shorter holding time (100 MPa and 5 s) resulted in the least changes in amino and fatty acids content of clams.

Effect of Different Cold Storage Temperatures on the Evolution of Shucking Yield and Quality Properties of Offshore Cultured Japanese Oyster (Magallana gigas) Treated by High Pressure Processing (HPP)

High pressure processing (HPP) can improve oyster shucking yield immediately after the treatment and increase the microbiological and sensory shelf life of oysters stored at 0–4 °C. However, the evolution of shucking yield during storage has not been previously examined and there are no studies focusing on shelf life at higher storage temperatures. To elucidate both aspects, control and HPP (300 MPa; 2 min) offshore cultivated oysters (Magallana gigas) were stored at 4 and 10 °C for 14 days, analyzing shucking yield, color, texture, microbiological and sensory characteristics. HPP samples showed a higher shucking yield (17% on average) than controls with minimal impact in texture and color, regardless of storage time and temperature. At 10 °C, HPP delayed microbial growth and sensory deterioration, increasing the estimated shelf life of oysters by 3 to 4 days (aerobic plate count < 6 log cycles; overall sensory acceptability > 2). Compared to controls stored at 4 °C, HPP oysters stored at 10 °C presented the same shelf life (5 to 9 days) but with higher shucking yield (up to 25%). In conclusion, HPP is an excellent tool to increase the shucking yield and delay sensory deterioration of oysters stored at 10 °C.

Replacing the Addition of Sulfite in Mustard Pickle Products by High-Hydrostatic-Pressure Processing to Delay Quality Deterioration during Storage

This study aimed to assess the use of the high-hydrostatic-pressure (HHP) method (200-600 MPa, 5 min) for bleaching mustard pickle products as an alternative to the conventional method of sulfite addition. The aerobic plate count (APC) and lactic acid bacteria count (LAB) of the samples decreased with the increase in pressure, and the yeast count decreased to no detectable levels. Next, compared with the control group (no high-pressure treatment) the L* (lightness), W (whiteness), ΔE (color difference), and texture (hardness and chewiness) of the HHP-processed samples, which increased significantly with increasing pressure, while the a* (redness) and b* (yellowness) values decreased slightly. This indicates that HHP processing gave the mustard pickle a harder texture and a brighter white color and appearance. Furthermore, when the mustard pickle was treated with HHP 400 and 600 MPa for 5 min and stored at 25 °C for 60 days, it was found that the APC and LAB counts in the HHP-processed group recovered rapidly and did not differ from those in the control group (the non-HHP treated group) but significantly delayed the growth of yeast, the increase in pH value, and total volatile basic nitrogen (TVBN). The high-throughput sequencing (HTS) analysis revealed that the predominant bacterial genera in the non-HHP-treated mustard pickle were Lactiplantibacillus (74%), Lactilactobacillus (12%), and Levilactobacillus (6%); after 60 days of storage, Companilactobacillus (80%) became dominant. However, after 60 days of storage, Lactiplantibacillus (92%) became dominant in the samples processed at 400 MPa, while Levilactobacillus (52%), Pediococcus (17%), and Lactiplantibacillus (17%) became dominant in the samples processed at 600 MPa. This indicated that the HHP treatment changed the lactic acid bacterial flora of the mustard pickle during the storage period. Overall, it is recommended to treat the mustard pickle with HHP above 400 MPa for 5 min to improve its texture and color and delay the deterioration of quality during storage. Therefore, HHP technology has the potential to be developed as a treatment technique to replace the addition of sulfite.

Inactivating Food Microbes by High-Pressure Processing and Combined Nonthermal and Thermal Treatment: A Review

High-pressure processing (HPP) is a mild technology alternative to thermal pasteurization and sterilization of different food products. HPP has emerged to provide enormous benefits to consumers, i.e., mildly processed food and additive-free food. It effectively retains bioactive compounds and extends the shelf life of food commodities by inactivating bacteria, yeast, mold, and virus. The limitation of HPP in inactivating spores can be overcome by using other thermal and nonthermal processing sequentially or simultaneously with HPP. This review summarizes the applications of HPP in the fruits and vegetables, dairy, meat, fish, and poultry sector. It also emphasizes microbial food safety and the effectiveness of HPP in the load reduction of microorganisms. Comprehensive information about the synergistic effect of HPP with different techniques and their effectiveness in ensuring food safety is reported. The summarized data would be handy to interested researchers and industry personnel.

High hydrostatic pressure combined with moisture regulators improves the tenderness and quality of beef jerky

The influence of high hydrostatic pressure (HHP) at different pressure levels (0.1, 100, 200, and 300 MPa) combined with moisture regulators (MR) on the tenderness, water content, and quality of beef jerky was investigated. HHP treatment reduced the shear force (SF) of beef jerky (P < 0.05). The beef jerky treated with MR+HHP exhibited higher tenderness than the beef jerky treated only with HHP (P < 0.05). The MR+HHP samples had significantly higher moisture content than the HHP samples (P > 0.05) when the water activity was maintained at approximately 0.7. MR+HHP contributed to a shorter T₂₁ value and a higher P₂₁ value, which indicated an improvement in the water-binding ability of the beef muscle. Analysis of the microstructure showed that MR+HHP led to the fracture of the Z-line and destruction of the sarcomere structure. Sensory analysis showed that MR+HHP-200 samples had significantly higher tenderness and overall acceptable scores than other samples (P < 0.05).

Quality characteristics of shucked crab meat (Eriocheir sinensis) processed by high pressure during superchilled storage

High-pressure processing (HPP) at 300 MPa for 20 min at 25°C was used for shucking Chinese mitten crab. The shelf-life, quality as well as internal protein changes in HPP-shucked meat were investigated during superchilled storage at -4^o C. Upon 3-week storage, the lightness and whiteness of HPP-shucked crab meat start to decline, while no significant changes were observed in the hardness, gumminess, and chewiness. Sensory and microbial evaluation suggested that HPP-shucked crab meat can be generally preserved in an acceptable manner within 3 weeks, although a negative influence on drip loss was found. The loss of entrapped water in crab meat as revealed by low field nuclear magnetic resonance was responsible for the relatively high thawing drip loss. The severe deterioration of meat quality and sensory occurred at 4-week storage probably as a result of exacerbated myofibrillar protein oxidation, denaturation, and crosslinking. PRACTICAL APPLICATIONS: It has been confirmed that HPP shucking can maintain the fresh-state of the crab meat and save energy compared to the conventional treatment, which could meet consumers' demand for minimally processed seafood products. In this work, the shelf-life of HPP-shucked crab meat stored at -4^o C was evaluated to be 3 weeks and HPP shucking combined with superchilling can be an effective way to preserve the crab meat. These results can provide basic knowledge for the storage and distribution of HPP-shucked crab meat.

Innovative Seafood Preservation Technologies: Recent Developments

Fish and fishery products are among the food commodities of high commercial value, high-quality protein content, vitamins, minerals and unsaturated fatty acids, which are beneficial to health. However, seafood products are highly perishable and thus require proper processing to maintain their quality and safety. On the other hand, consumers, nowadays, demand fresh or fresh-like, minimally processed fishery products that do not alter their natural quality attributes. The present article reviews the results of studies published over the last 15 years in the literature on: (i) the main spoilage mechanisms of seafood including contamination with pathogens and (ii) innovative processing technologies applied for the preservation and shelf life extension of seafood products. These primarily include: high hydrostatic pressure, natural preservatives, ozonation, irradiation, pulse light technology and retort pouch processing.

Quantification of the Flavor and Taste of Gonads from the Sea Urchin Mesocentrotus nudus Using GC-MS and a Taste-Sensing System

Sea urchin gonads are a delicious seafood item of high commercial value. Our past studies have revealed that the gonads of the sea urchin Mesocentrotus nudus fed the basal frond portion of fresh Saccharina kelp (BS) or the sporophylls of fresh Undaria (SU) during May–July are of high-quality. The present study investigated the flavor and taste of BS and SU gonads in comparison with those from non-fed M. nudus (NF) using gas chromatography–mass spectrometry (GC–MS) and gas chromatography (GC)-sniffing techniques, and a taste-sensing system. Data of the estimated intensity of taste (EIT) were compared with assessment of gonads from M. nudus collected from an Eisenia bed (fishing ground) and a barren in July. Gonads from both BS and SU released pleasant green, sour, and fruity aromas characteristic of butyl acetate, which are here recognized essential flavor components of high-quality gonads. The gonads of BS and SU had a strong umami taste compared to those of NF, and the Eisenia bed and the barren. The most marketable M. nudus gonads were assessed to be those with green and fruity aromas from butyl acetate, sweet aroma from benzaldehyde, umami EIT > 13.8, bitterness EIT < 3.1, and without any unpleasant sulfurous odor from sulfur-containing compounds.

Comparison of biochemical composition and non-volatile taste active compounds in raw, high hydrostatic pressure-treated and steamed oysters Crassostrea hongkongensis

In this study, the effects of high hydrostatic pressure (HHP) and steam on biochemical composition and non-volatile taste active compounds of oysters Crassostrea hongkongensis were investigated. The moisture content in steamed oysters significantly decreased when compared to raw samples, subsequently their crude protein, crude lipid, glycogen and ash contents (% wet weight) were all increased (P < 0.05). In addition, though the moisture content in HHP oysters decreased, no significant differences were observed in proximate compositions compared to raw oysters, except crude protein. There were no significant differences in saturated fatty acids (SFA), monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) profiles between raw and HHP oysters, however, C20:3n6 content in HHP oysters was significantly higher than that in raw samples (P < 0.05). The PUFA profile of steamed oysters, mostly contributed by n-3 PUFA, was significantly higher than that of both raw and HHP samples (P < 0.05). Major free amino acids (FAA) (taste activity value, TAV > 1) in oysters with three treatments were alanine, glycine, glutamic acid and histidine, and their contents were significantly higher in raw and HHP groups than that in steamed group. The 5'-inosine monophosphate (IMP) and 5'-guanosine monophosphate (GMP) in HHP and steamed oysters decreased compared to raw samples, while AMP content in steam oysters were significantly increased (P < 0.05). The equivalent umami concentration (EUC) of oysters of raw, HHP and steamed groups were 8.80, 3.66 and 1.44 g MSG/100 g, respectively, with significant differences observed among different treatments (P < 0.05). Succinic acid was the major organic acid in raw and HHP oysters, while lactic acid was the major organic acid in steamed groups. Further, Na⁺, K⁺, PO₄^3- and Cl^- were the main inorganic ions (TAV > 1), and their contents were significantly higher in raw and HHP groups than that in steamed group (P < 0.05). This study demonstrated that HHP treatment slightly influenced the changes in the biochemical composition and non-volatile taste active compounds to raw oysters, compared to steamed process.

Physicochemical, microbiological and sensory quality changes of tissues from Pacific oyster (Crassostrea gigas) during chilled storage

This study was designed to investigate the changes of physicochemical, microbiological and sensory properties of oyster tissues during chilled storage at 4 °C, including digestive gland (DG), the gonad and surrounding mantle area (GM), adductor muscle (AM). Sensory evaluation showed that the decrease of sensory scores of the three oyster tissues was more rapid than the whole oyster (WO). The drip loss of DG was more than other tissues and the WO. Moreover, the GM showed higher extent of lipid oxidation than other tissues and WO, while the AM showed higher TVB-N value and microbial counts than other tissues and WO. It is concluded that the spoilage of oyster during chilled storage greatly depended on the composition of oyster tissues. Overall, the findings may provide new insights to control the spoilage of oyster based on the changes of oyster tissues during storage.

Odor-active compounds from the gonads of Mesocentrotus nudus sea urchins fed Saccharina japonica kelp

Gonad size, color, texture and taste of Mesocentrotus nudus sea urchins collected from a barren can be improved by a short-term cage culture while being fed fresh Saccharina japonica kelp during May-July. We investigated the effect of S. japonica feeding during May-July on the improvement of gonad flavor in M. nudus collected from a barren. After feeding, we analyzed the odor-active volatile organic compounds (VOCs) from the gonads using gas chromatography-mass spectrometry and GC-sniffing analyses and compared to those from the gonads of wild sea urchins from an Eisenia kelp bed (fishing ground) and a barren. A total of 48 VOCs were detected from the gonads of cultured and wild sea urchins. Of them, a larger number of odor-active compounds were detected in the gonads of cultured sea urchins (25) than in those from the Eisenia bed (14) and the barren (6). Dimethyl sulfide from the gonads of sea urchins from the barren was described as having a strong, putrid odor. Sea urchin-like aromas were attributed to 2-butanol, 2-ethylhexanol, benzaldehyde and ethylbenzene from the gonads of cultured sea urchin and those of the Eisenia bed. Kelp feeding decreased the putrid odor from dimethyl sulfide, and enhanced pleasant, sweet aromas.

Effect of High-Pressure Processing (HPP) on the Fatty Acid Profile of Different Sized Ragworms (Hediste diversicolor) Cultured in an Integrated Multi-Trophic Aquaculture (IMTA) System

Ragworms (Hediste diversicolor) cultured under integrated multi-trophic aquaculture (IMTA) conditions display an improved fatty acids (FA) profile than conspecifics from the wild, thus being more suitable for maturation diets of marine fish and shrimp. Nonetheless, their use may represent a potential pathway for pathogens. The objective of the present study was to determine if high-pressure processing (HPP), as an approach to safeguard microbiological safety, could promote significant shifts on the FA profiles of different sized ragworms. An analysis of similarities (ANOSIM) revealed the existence of significant differences in the FA profile and lipid quality indexes (atherogenicity (AI), thrombogenicity (TI) and polyene (PI)) of control and HPP treated ragworms of all tested sizes (small, medium and large). Saturated (SFA) and monounsaturated FA (MUFA) increased after HPP, while polyunsaturated FA (PUFA; FA with 2 or 3 double bonds) and highly unsaturated FA (HUFA; FA with ≥ 4 double bonds) decreased. The amount of docosahexaenoic acid (DHA) in polychaetes exposed to HPP decreased an average of 25%, when compared with the levels recorded in control groups. The values of PI significantly decreased after HPP, while those of AI and TI displayed a significant increase. Despite the shifts in the FA profile of ragworms exposed to HPP, these still display a superior profile to that of wild specimens, namely the presence of DHA. Therefore, HPP can be considered as a suitable approach to safeguard the biosecurity of cultured polychaetes, without compromising their nutritional value, and support the principles of circular economy through the use of IMTA.

Effects of high hydrostatic pressure-assisted thawing on the physicohemical characteristics of silver pomfret (Pampus argenteus)

Effects of high hydrostatic pressure-assisted thawing (HPAT, 100, 150, and 200 MPa) on the physicochemical characteristics of silver pomfret were evaluated in comparison with conventional (water immersion thawing, WIT) thawed samples. HPAT significantly decreased the thawing time, as well as the cooking and total losses. The maximum water holding capacity was observed at 100 MPa. Color changed obviously at ≥150 MPa, resulting in a cooked appearance. Samples thawed with HPAT showed better texture quality and lower lipid oxidation. The levels of myofibrillar protein oxidation and surface hydrophobicity increased, while Ca2+-ATPase activities decreased as the pressure increased. The oxidation of myofibrillar protein was significantly decreased at 100 MPa; total sulfhydryl content was 30.85% higher than that of WIT. Overall, 100 MPa is the optimum treatment condition for silver pomfret thawing without negative effects on quality of the product. HPAT can be a potential alternative to produce high-quality thawed fish.

Principles and recent applications of novel non-thermal processing technologies for the fish industry-a review

Thermal treatment is a traditional method for food processing, which can kill microorganisms but also lead to physicochemical and sensory quality damage, especially to temperature-sensitive foods. Nowadays consumers' increasing interest in microbial safety products with premium appearance, flavor, great nutritional value and extended shelf-life has promoted the development of emerging non-thermal food processing technologies as alternative or substitution to traditional thermal methods. Fish is an important and world-favored food but has a short shelf-life due to its extremely perishable characteristic, and the microbial spoilage and oxidative process happen rapidly just from the moment of capture, making it dependent heavily on post-harvest preservation. The applications of novel non-thermal food processing technologies, including high pressure processing (HPP), ultrasound (US), pulsed electric fields (PEF), pulsed light (PL), cold plasma (CP) and ozone can extend the shelf-life by microbial inactivation and also keep good sensory quality attributes of fish, which is of high interest for the fish industry. This review presents the principles, developments of emerging non-thermal food processing technologies, and also their applications in fish industry, with the main focus on microbial inactivation and sensory quality. The promising results showed great potential to keep microbial safety while maintaining organoleptic attributes of fish products. What's more, the strengths and weaknesses of these technologies are also discussed. The combination of different food processing technologies or with advanced packaging methods can improve antimicrobial efficacy while not significantly affect other quality properties under optimized treatment.

Delaware Inland Bays and Market Oyster (Crassostrea virginica) Quality for Consumption

Consumption of raw oysters is known to cause serious health conditions due to bioaccumulation of contaminants. As filter feeders, oysters ingest bacteria along with phytoplankton from their surrounding habitats. Ensuring seafood safety for human consumption is always a concern. Since oysters are consumed raw, disease causing organisms, environmental contaminants, toxins, chemicals, and even physical hazards such as soils and metals retained in the oysters can enter through feeding. The objective of this study was to determine the quality of oysters collected from Delaware Inland Bays (DIB) and compare them with market oysters. Environmental parameters were monitored from local waters of DIB classified as closed versus open for shellfish harvesting. Total aerobic bacteria and vibrio were higher in market oysters during the warmer months, with open water having the least microbial loads. There were no significant differences in total vibrio counts between the study sites (p=0.396), but significant differences were recorded over time (p=0.004). Water temperature and turbidity were directly proportional to total vibrio in oysters, and salinity was inversely related. Research findings in this study may help bring awareness of changes in bacterial loads due to seasonal changes and additional handling and storage.

Impact of High Hydrostatic Pressure on the Shelling Efficacy, Physicochemical Properties, and Microstructure of Fresh Razor Clam (Sinonovacula constricta)

The effects of high hydrostatic pressure (HHP) treatments (200, 300, and 400 MPa for 1, 3, 5 and 10 min) on the shelling efficacy (the rate of shelling, the rate of integrity and yield of razor clam meat) and the physicochemical (drip loss, water-holding capacity, pH, conductivity, lipid oxidation, Ca²⁺ -ATPase activity, myofibrillar protein content), microbiological (total viable counts) and microstructural properties of fresh razor clam (Sinonovacula constricta) were investigated. HHP treatments significantly (P < 0.05) increased shelling efficiency, water-holding capacity, pH, conductivity, and lipid oxidation, and HHP-treated razor clam showed lower levels of microorganisms and drip loss than untreated razor clam. Levels of thiobarbituric acid reacting substances (TBA) in HHP-treated razor clam were greatly increased (up to 0.93 ± 0.09 mg MDA/kg at 400 MPa for 10 min) which was caused by the formation of hydroperoxides during HHP treatment. All HHP treatments were found to have adverse effects on the activity of Ca²⁺ -ATPase and the content of myofibrillar protein (MP), which might be due to the substantial damage to the tertiary structure of proteins at high pressure. Moreover, scanning electron microscopy (SEM) revealed the compaction of the muscle fibers and a decrease in the extracellular space with increasing pressure and holding time. This phenomenon was mainly correlated with the compaction of muscle fibers and denaturation, aggregation, and gelation of muscle protein triggered by high pressure. In general, HHP could be applied as a safe and effective nonthermal technology to produce high-quality shelled razor clam.

PRACTICAL APPLICATION

High hydrostatic pressure (HHP) is now well known as a nonthermal processing technology and becoming increasingly acknowledged. However, it has not been widely applied to shell seafood due to its uncertain influence on its quality and shelling property. This study could provide valuable information regarding the shelling efficacy, physicochemical properties, and microstructure of razor clam treated by HHP. And it demonstrated that HHP showed a positive impact on quality of razor clam treated by HHP.

Seafood spoilage microbiota and associated volatile organic compounds at different storage temperatures and packaging conditions

Seafood comprising of both vertebrate and invertebrate aquatic organisms are nutritious, rich in omega-3 fatty acids, essential vitamins, proteins, minerals and form part of healthy diet. However, despite the health and nutritional benefits, seafood is highly perishable. Spoilage of seafood could be as a result of microbial activity, autolysis or chemical oxidation. Microbial activity constitutes more spoilage than others. Spoilage bacteria are commonly Gram negative and produce off odours and flavours in seafood as a result of their metabolic activities. Storage temperature, handling and packaging conditions affect microbial growth and thus the shelf-life of seafood. Due to the complexity of the microbial communities in seafood, culture dependent methods of detection may not be useful, hence the need for culture independent methods are necessary to understand the diversity of microbiota and spoilage process. Similarly, the volatile organic compounds released by spoilage bacteria are not fully understood in some seafood. This review therefore highlights current knowledge and understanding of seafood spoilage microbiota, volatile organic compounds, effects of storage temperature and packaging conditions on quality of seafood.

Effects on the Qualities of Proteolysis to Beef by Non-coating and Coating Protease Treatment

This study was performed to improve the techniques used for tenderizing red meat as elderly food. Beef meat was immersed in liposome encapsulated enzyme solution and the effect of protease encapsulation on the beef properties was analyzed. The protease encapsulation properties were analyzed according to the size distribution and enzymatic activity. After enzyme reaction on the beef, the chemical properties of the meat such as pH, water holding capacity, shear rate, lipid oxidation and total volatile basic nitrogen (TVB-N) were analyzed. The pH of the beef increased during the reaction and coating protease (CP) was higher than non-coating protease (NCP). Total color differences were increased remarkably after 36 h and generally, the difference in CP was relatively lower than in NCP. WHC was significantly decreased within 24 h, and no effect from the protease coating was observed. Protease activity was significantly increased within 48 h and no differences in the enzyme coating were observed. The TVB-N value of NCP was increased within 24 h while CP was sustained for up to 36 h. The TVB-N value of protease treated meat increased after 36 h and no effect from the protease coating was detected. Consequently, liposome encapsulated protease was found to have similar properties as non-coated protease. Application of liposome seems to be an interesting option for injecting various functional materials without changing the properties of meat.

Changes in the microbiological quality of mangrove oysters (Crassostrea brasiliana) during different storage conditions

This study aimed to determine the effect of temperature and period of postharvest storage on the microbiological quality and shelf life of raw mangrove oysters, Crassostrea brasiliana. A total of 150 dozen oysters were collected directly from the points of extraction or cultivation in southern Brazil, and in the laboratory, they were stored raw at 5, 10, 15, 20, and 25°C for 1, 4, 8, 11, and 15 days. On each of these days, the oysters were subjected to microbiological analyses of aerobic mesophilic count, total coliforms, enterococci, Escherichia coli, Staphylococcus aureus, and Salmonella. None of the tested samples under any storage condition showed contamination levels above those allowed by Brazilian legislation for E. coli, S. aureus, and Salmonella, and there was no change (P > 0.05) in the counts of these microorganisms due to the temperature and/or period of oyster storage. Counts of enterococci and total coliforms showed a tendency to increase (P < 0.05) among the different temperatures tested. Raw mangrove oysters remain in safe microbiological conditions for consumption up to 8 days after harvesting, regardless of temperature, and their shelf life may be extended to 15 days if they are stored at temperatures not exceeding 15°C.

Physicochemical Properties of Chilled Abalone as Influenced by Washing Pretreatment in Citric Acid Combined with High Pressure Processing

Citric acid pretreatment (2% and 4% citric acid) and high pressure processing (200–400 MPa for 3 min) were conducted to elucidate quality characteristics and shelf life of abalone during chilled storage. Physicochemical properties, total volatile basic nitrogen (TVB-N), and total viable count (TVC) were used as indicators of quality and the shelf life of abalone. Citric acid pretreatment caused a decrease in pH and lightness, and 4% citric acid pretreatment exhibited a positive effect on TVB-N and TVC. Pressurization suppressed the formation of TVB-N and the growth of TVC in abalone. However, excessive modification in physicochemical properties of abalone resulted from processing at a pressure higher than 300 MPa. To achieve microbial inactivation without severe modification in abalone quality, citric acid pretreatment with high pressure processing offered a potential advantage in maintaining characteristics of chilled abalone during prolonged storage period.

Effect of high pressure treatment on microbiological quality of Indian white prawn (Fenneropenaeus indicus) during chilled storage

High pressure treatment of 250 MPa for 6 min at 25 °C was applied to headless Indian white prawn (Fenneropenaeus indicus) to evaluate changes in microbiological characteristics of the species during chilled storage. Changes in load of mesophilic bacteria, psychrotrophic bacteria, proteolytic bacteria, Enterobacteriaceae, Pseudomonas spp., H2S producing bacteria, lactic acid bacteria, Brochothrix thermosphacta and yeast & mold were estimated in pressurized and un-pressurized samples during chilled storage. All microbes were reduced significantly after high pressure treatment and there was significant difference in microbial quality of control and high pressure treated samples in the entire duration of chilled storage (p < 0.05). There was delay in the growth of Enterobacteriaceae and H2S producing bacteria up to 6th and 9th day of storage, respectively in high pressure treated samples. In high pressure treated sample, no lag phase (λ) was observed for psychrotrophic bacteria, H2S producing bacteria, B. thermosphacta, Pseudomonas spp. and lactic acid bacteria; however, other bacteria showed a reduced lag phase during chilled storage. Kinetic parameter such as specific growth rate (μmax) in high pressure treated samples was significantly reduced in most of the bacterial groups except for psychrotrophic bacteria, Enterobacteriaceae and lactic acid bacteria. Mesophilic bacterial count of control samples crossed the marginal limit of acceptability on 12th day and unacceptable limit on 18th day of storage, whereas high pressure treated samples never breached the acceptability limit during entire duration of chilled storage. The present study indicated that application of high pressure processing can be used to improve microbial quality of Indian white prawn and extend the chilled storage life.

Characterisation of the spoilage bacterial microbiota in oyster gills during storage at different temperatures

BACKGROUND

The spoilage bacterial community in oyster gill was investigated during storage at 4, 10 and 20 °C. Aerobic plate counts and pH values were determined. Total bacterial DNA was extracted from oyster gill and bulk cells of plate count media. The major bacterial species during fresh or different temperatures storage were determined by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE).

RESULTS

The initial aerobic plate count in oyster gill reached 6.70 log CFU g(-1). PCR-DGGE fingerprinting analysis of the 16S rRNA gene V3 region revealed that most of the strains in fresh oyster gill belonged to the genera Lactococcus and Enterobacter. The major spoilage bacteria at a storage temperature of 20 °C were Leuconostoc pseudomesenteroides, an uncultured bacterium, Cytophaga fermentans, Lactococcus lactis, Pseudoalteromonas sp., Enterococcus mundtii, Clostridium difficile and an uncultured Fusobacteria; those at 10 °C were Lactococcus spp., Lactobacillus curvatus, Weissella confusa and C. difficile; those at 4 °C were Lactococcus, Weissella, Enterobacter and Aeromonas. The other minor species were L. curvatus, Pseudomonas sp. and E. mundtii. Lactococcus spp. was the most common main spoilage bacteria in oyster gill during chilled storage.

CONCLUSION

PCR-DGGE revealed the complexity of the bacterial microbiota and the major bacteria species in oyster gill for fresh and storage.

Effects of high pressure processing on fatty acid composition and volatile compounds in Korean native black goat meat

This study investigated the effects of high pressure processing (HPP) on fatty acid composition and volatile compounds in Korean native black goat (KNBG) meat. Fatty acid content in KNBG meat was not significantly (p > 0.05) different among the control goats and those subjected HPP. The 9,12-octadecadienoic acid and octadecanoic acid, well-known causes of off-flavors, were detected from meat of some KNBG. A difference between the control and HPP treatment was observed in the discriminated function analysis using an electronic nose. The results suggest that the volatile compounds in KNBG meat were affected by HPP.