Quality Of Oysters Research Articles

Heritability estimates for nutritional quality‐related traits of the Pacific oyster, Crassostrea gigas

Pacific oysters, Crassostrea gigas, are the most abundantly harvested shellfish in the world and are ecologically significant. The content of nutrients, including protein, glycogen, lipid, zinc (Zn), and selenium (Se), is important for oyster meat quality, but heritability estimates of such traits have rarely been reported. In this study, 64 full‐sib families were generated using a nested mating design. Finally, 18 full‐sib families, of which there were nine half‐sib families, with each containing 2 full‐sib families, were sampled for heritability estimates. The narrow‐sense heritabilities of glycogen, protein, lipid, Zn, and Se contents were 0.29 ± 0.02, 0.38 ± 0.02, 0.58 ± 0.08, 0.02 ± 0.02, and 0, respectively. Negative genetic correlations existed between both glycogen and protein content (−0.95 ± 0.004) and between lipid and protein content (−0.59 ± 0.05), whereas a positive correlation was observed between lipid and glycogen content (0.16 ± 0.06). Weak genetic and phenotypical correlations (r = 0–0.2) were observed between shell height and nutritional quality traits. These data demonstrated that glycogen, protein, and lipid content can be chosen in a selective breeding program, but glycogen and lipids cannot be selected together with protein. Furthermore, performing indirect selective breeding for quality traits by selecting traits related to growth is impossible. This study provides information for the development of breeding strategies for oyster quality traits.

Effects of Modified Atmospheric Packaging Conditions on the Quality Changes of Pasteurized Oyster (Crassostrea belcheri) Meat during Chilled Storage

ABSTRACTThe effects of different atmospheric conditions on the quality and the shelf life of pasteurized oyster meat in chilled storage were investigated. The alternatives tested for pasteurized oyster meat were normal air (Control), 75% CO2/25% N2 (MAP-1), 75% CO2/25% O2 (MAP-2), 75% CO2/5% O2/20% N2 (MAP-3), and vacuum packing (VP). The various observations of microbiological (total viable count (TVC), Enterobacteriaceae, Pseudomonas spp., lactic acid bacteria (LAB), and hydrogen sulfide–producing bacteria), physical (color coordinates L*, a*, and b*, and cutting strength), chemical (moisture, pH, total volatile basic nitrogen (TVB-N), peroxide value (PV), and thiobarbituric acid reactive substances (TBARS)) and sensory properties were performed every 3 days over a total of 27 days. During storage across all the treatments, L*, a*, cutting strength, pH, moisture content, and sensory scores decreased; whereas, b*, TVB-N, PV, TBARS, and microorganisms increased. However, among the various alternatives, MAP-1 had the best retention of oyster quality during storage. Based on sensory and microbiological qualities, the shelf lives in chilled storage were 9 days for control, 15 days for VP, 21 days for MAP-2 and MAP-3, and 24 days for MAP-1-treated cases.

Bacteriological Quality of the Mangrove Oyster (Crassostrea rhizophorae) in the Swamp of Mestizo - Cordoba (Colombia)

Objectives: To determine the bacteriological quality of the mangrove oyster and its aquatic environment, such as a risk factor in public health, through the consumption of these products from the natural environment. Materials and Methods: Data were collected about 60 samples of oysters and the surrounding water, between June and November 2004. Using the indirect method of counting multiple fermentation tubes, we estimated the concentration of bacteria indicators of total and fecal coliform contamination. The indicators of the bacteriological quality of the oysters presented a minimum of ≤ 3 NMP.100 mL-1 and a maximum of 46 × 104 MPN.100 mL-1 of total coliforms, fecal coliforms showed a seasonal variation in concentrations between ≤3 NMP.100 mL-1 and 2 × 103 MPN.100 mL-1 . Findings: The analysis of water samples recorded a range of concentration of coliforms from ≤ 3 NMP.100 mL-1 to 3.9 × 105 NMP.100 mL-1 and for fecal coliforms it ranged from ≤ 3 NMP.100 mL-1 to 7 × 103 MPN.100 mL-1 . This study suggests that there exists a directly proportional relationship between the bacteriological quality of the mangrove oyster Crassostrea rhizophorae and the water quality of the environment, by its status filtering, which contributes a factor of risk to public health, the consumption of this food, especially if the consumption is done in a direct way. Applications/recommendations: the potentiality of the Bay of Mestizo, Colombia, for the development of a sustainable aquaculture of the mangrove oyster (Crassostrea rhizophorae), requires baseline studies on various environmental and social aspects which will lay the basis for the socio-economic development of this region. Keywords: Molluscs, total coliforms, fecal coliforms, sustainable aquaculture, public health.

Marine Circular Economy towards Post-Disaster Reconstruction for Sustainability: Experiences in a Small Coastal Town of Northeast Japan

The wealth of evidence on the conservation effects of development and utilization of ocean, whereas what shapes behavioral change remains unknown, particularly of fishermen. Few previous studies incorporate measuring changes in fishermen’s behavior. This study aims to investigate what changed behavior and perception of fishermen toward marine circular economy in Japan. We selected a unique case of marine-linked practical change of fishermen’s behavior. Our study area, Minamisanriku town in Miyagi Prefecture, was affected in the 2011 earthquake and tsunami. The town incorporated marine circular economy (MCE) into post-disaster reconstruction project: Fishermen reduced farming facilities to one-third of that before the disaster and the quality of oyster improved. To indicate the determinant facts of the practical change, we used ordered probit model for fishermen recognition on the effectiveness of integrating marine conservation into post-disaster reconstruction. Our main finding was different recognition level existed amongst fishermen. It was associated with branch affiliation and hope level for the sustainable fishing culture by the next generation. This study provides understanding a tangible and measurable change in recognition can be bridge the gap between idea and practice. This study suggests horizontal collaboration among between branches would lead to marine conservation attitude through community-based post-disaster reconstruction. Keywords: Marine circular economy, fishermen’s recognition, post-disaster reconstruction, Japan

Quality perception, purchase intention, and the impact of information on the evaluation of refined Pacific cupped oysters (Crassostrea gigas) by Dutch consumers.

BACKGROUNDOyster refinement using land‐based pond systems is a new activity in the Dutch oyster sector. It increases the oyster's tissue weight and changes its sensorial properties. However, the response of Dutch consumers towards refined oysters is unknown. The research aim was to gain insight into the importance of oyster quality parameters, drivers for oyster consumption, and acceptance of refined oysters by Dutch consumers, taking into account the information given to them about the product and process.RESULTSTaste, texture, and odor are the most important oyster quality characteristics for Dutch consumers. The outcome of questionnaires showed that willingness to buy and pay is influenced by factors such as the oysters' country of origin, cultivation area, and flavor profile. Refinement did not affect willingness to buy and pay. Furthermore Dutch consumers seem to have a preference for the flavor profile of refined oysters. Consumer evaluation showed that refined Pacific cupped oysters were perceived as sweeter compared with non‐refined oysters. When information on the cultivation process was disclosed, overall appreciation of refined oysters by consumers increased.CONCLUSIONNew insights in the importance of oyster quality characteristics for Dutch consumers are generated that can be used in the development of refined Pacific cupped oysters. © 2018 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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.

Seeking the perfect oyster shell: a brief review of current knowledge

AbstractCurrent trends in the seafood market indicate increased demand for within‐shell oysters, associated with increasing popularity of oyster bars. As this specialized, demanding market increases globally, there is strong incentive to improve quality. In this context, the manipulation of oyster shell traits through aquaculture as a means of improving oyster quality is timely and promising in terms of marketing. Several oyster shell characteristics, most especially shape, measured as length (L), width (W) and depth (D), result from a combination of three factors: genetics, environmental condition to which the oyster is exposed and husbandry practices. Although breeding programmes have targeted several important commercial traits, selection for shell traits has not been widely performed. Additionally, accumulated knowledge of the effects of environmental conditions and farming methods on shell characteristics exists at a local level, but as such, it is not always validated with scientific data. The existing local knowledge and practices, however, are of extreme importance for the improvement and adaptation of the farming sector to market demands. Current knowledge about the genetic, environmental and husbandry effects on shell and related aquaculture practices for manipulation of shell appearance and robustness in commercially important oysters of the Genus Crassostrea is compiled here. As the topic has not been well documented in the academic field, information from scientific articles was complemented by technical reports and commercial sources. A combination of aquaculture practices is needed to produce oysters of acceptable shape, thickness, cleanliness and colour, although suitable shell characteristics may vary with different markets.

초고압 처리한 생굴의 압력별 탈각 성능과 관능적 특성 변화

We developed an automatic oyster separating machine using high hydrostatic pressure, and conducted research related to improving the working environment and increasing production volume. Changes in the by pressure cast off performance and sensual properties of raw oysters (Crassostrea gigas) treated with high hydrostatic pressure were evaluated. At a pressure of 175 MPa or more, the shell removal rate was over 90%. Samples automatically separated using high hydrostatic pressures of 250 MPa, 200 MPa, and 175 MPa together with a manually separated sample were evaluated using a seven-point rating scale for appearance (color, shape), smell, taste (salty, fishy), texture, and preference. The manually separated sample had similar rating values to the 175 MPa automatically separated sample. In conclusion, it is necessary to continue evaluation of the machine’s performance, sensory evaluation, oyster quality improvement oysters and development of technology for future commercialization.

Characterization of microbial community in high-pressure treated oysters by high-throughput sequencing technology

Abstract High-pressure (HP) processing technology has great application potential in bivalve mollusk industry. In this study, the effects of HP treatment on shucking and shelf-life extension of Pacific oysters (Crassostrea gigas) during 4 ± 1 °C storage were studied. Culture-independent high-throughput sequencing (HTS) technology was used to investigate the microbiota of oysters treated by HP (300 MPa, 2 min) during storage. Results showed that HP treatment at 275 MPa for 3 min or 300 MPa for 2 min could achieve 100% full release of oyster adductor muscle, pressures higher than 300 MPa caused disadvantageous damage of shells. Therefore, HP treatment at 300 MPa for 2 min was particularly appropriate. Based on organoleptic, biochemical and microbiological analyses, shelf-life of 6–8 days for control and 12 days for HP-treated oysters could be expected. The dominant bacteria in fresh oysters were Vibrio (28.3%), Shewanella (10.3%) and Pseudoalteromonas (7.2%). HP treatment changed the spoilage microbiota of oysters dramatically. Psychrobacter was dominant in the HP-treated spoiled oysters and its proportion was 42.3%, while Pseudoalteromonas (32.2%) and Shewanella (19.5%) were dominant in the spoiled oysters without HP treatment. This study confirmed that HP processing was effective in facilitating the removal of oyster meats from the shells and prolonging their shelf-life. More importantly, HP treatment changed the microbiota of oysters during chilled storage. Industrial relevance As seafood, oysters have a short shelf-life. High-pressure (HP) processing technology has showed great application potentials in the bivalve mollusk industry. In this work, we determined the effects of HP treatment on the shucking and shelf-life extension of oysters. We used high-throughput sequencing technology to investigate the microbiota of control and HP-treated oysters during refrigerated storage. We found that HP treatment changed the spoilage microbiota of oysters dramatically. Psychrobacter was dominant in the HP-treated spoiled oysters, while Pseudoalteromonas and Shewanella were dominant in the spoiled oysters without HP treatment. Therefore, controlling the growth of Psychrobacter could help to improve the quality of oysters treated by HP during storage.

Sensory Qualities of Oysters Unaltered by a Short Exposure to Combined Elevated pCO2 and Temperature

Reliance on the marine environment for the provision of food is ever-increasing, but future climate change threatens production. Despite this concern, the impact on seafood quality and success of the seafood industry is unknown. Using a short-term study, we test these concerns using a major aquaculture species – Crassostrea gigas – exposing them to three acidification and warming scenarios: 1) ambient pCO2 (~400 ppm) & control temperature (15°C) 2) ambient pCO2 (~400 ppm) & elevated temperature (20°C), 3) elevated pCO2 (~1000 ppm) & elevated temperature (20°C). Oyster quality was assessed by scoring appearance, aroma, taste, and overall acceptability. A panel of five experts was asked to score nine oysters – three from each treatment – according to agreed criteria. Results indicate that these levels of acidification and warming did not significantly alter the sensory properties of C. gigas, and notably the overall acceptability remained unchanged. Non-statistically supported trends suggest that several sensory attributes – opacity, mouthfeel, aspect of meat, shininess, meat resistance, meat texture, and creaminess – may improve under acidification and warming scenarios. These findings can be considered positive for the future of the aquaculture and food sectors. Crassostrea gigas therefore is expected to remain a key species for food security that is resilient to climate change, whilst retaining its valuable attributes.

Quality aspects of Crassostrea gigas (Thunberg, 1793) reared in the Varano Lagoon (southern Italy) in relation to marketability

Shellfish culture, based on ecological and market assessment, is considered a driving force for socio-economic change in ecologically complex coastal systems such as lagoons throughout the Mediterranean area. To diversify fish production, the Pacific oyster Crassostrea gigas was cultured at commercial farms in the Varano Lagoon (SE Italy). The aims of this study were to evaluate through four condition indices (CI, CICG, CIE and AFNOR index), the Polydora index (PI), lipid content, quality and market aspects of oysters reared at two different sites (FO and LA) of the Varano Lagoon, which are characterized by different hydrodynamic conditions. The results of this study highlighted the potential economic benefits associated with sustainable aquaculture development in the Varano Lagoon, proving that the area surrounding the LA site was more suitable for oyster culture, reaching commercial size (60 mm) in a shorter time (6–8 months). Higher growth performance of oysters was observed in the spring, when the nutrient availability positively affected the feeding response of suspension feeders. The opposite was found in winter and in summer, when the decrease in growth could be due to the reduction of nutrient and to the increase of salinity, TSM and ISM. The presence of the mud blister worm (Polydora sp.) during rearing could be a real problem, as it damages oyster market value and threatens serious financial loss to the local farmers.

Integrated application of transcriptomics and metabolomics provides insights into glycogen content regulation in the Pacific oyster Crassostrea gigas

BackgroundThe Pacific oyster Crassostrea gigas is an important marine fishery resource, which contains high levels of glycogen that contributes to the flavor and the quality of the oyster. However, little is known about the molecular and chemical mechanisms underlying glycogen content differences in Pacific oysters. Using a homogeneous cultured Pacific oyster family, we explored these regulatory networks at the level of the metabolome and the transcriptome.ResultsOysters with the highest and lowest natural glycogen content were selected for differential transcriptome and metabolome analysis. We identified 1888 differentially-expressed genes, seventy-five differentially-abundant metabolites, which are part of twenty-seven signaling pathways that were enriched using an integrated analysis of the interaction between the differentially-expressed genes and the differentially-abundant metabolites. Based on these results, we found that a high expression of carnitine O-palmitoyltransferase 2 (CPT2), indicative of increased fatty acid degradation, is associated with a lower glycogen content. Together, a high level of expression of phosphoenolpyruvate carboxykinase (PEPCK), and high levels of glucogenic amino acids likely underlie the increased glycogen production in high-glycogen oysters. In addition, the higher levels of the glycolytic enzymes hexokinase (HK) and pyruvate kinase (PK), as well as of the TCA cycle enzymes malate dehydrogenase (MDH) and pyruvate carboxylase (PYC), imply that there is a concomitant up-regulation of energy metabolism in high-glycogen oysters. High-glycogen oysters also appeared to have an increased ability to cope with stress, since the levels of the antioxidant glutathione peroxidase enzyme 5 (GPX5) gene were also increased.ConclusionOur results suggest that amino acids and free fatty acids are closely related to glycogen content in oysters. In addition, oysters with a high glycogen content have a greater energy production capacity and a greater ability to cope with stress. These findings will not only provide insights into the molecular mechanisms underlying oyster quality, but also promote research into the molecular breeding of oysters.

Initial Freshness of Pacific Oyster (<i>Crassostea gigas</i>) Affects Its Quality and Self-life during Freezing Storage

We investigated the effect of initial freshness of raw oysters on the quality and storage period of oysters during freezing storage. The expressible drips of the oysters were more effused as the freezing storage period increased. Also, the lower the initial freshness of the oysters, the more drips were released after thawing. The pH values decreased slightly during freezing storage at -20 °C for 12 months, but there was no significant difference (p > 0.05) according to initial freshness of raw oysters. The initial glycogen contents of oysters before freezing was between 722 and 585 mg/100 g whereas the glycogen contents of the oysters after freezing for 12 months ranged from 667 to 522 mg/100 g. The initial TVB-N value of S-1 with freshness of “good quality” was 3.9 mg N/100 g, but gradually increased during the freezing storage period and its value was 7.9 mg N/100g at 12 months of storage. S-7 of with an initial TVB-N value of 15.2 mg N/100 g increased sharply during freezing storage, reaching a maximum of 36.2 mg N/100g at 8 months after storage and then slightly decreased to 32.2 mg N/100g at 12 months of storage. S-5 with an initial PV of 12.6 meq/kg showed the highest value of 33.7 meq/kg at the 10 months of storage and S-7 with an initial PV of 17.5 meq/kg showed the highest value of 44.6 meq/kg at 8 months of storage. PL of oysters decreased with increasing storage period regardless of their initial freshness in all samples, while FFA increased during freezing storage The scores of all sensory evaluation parameters of S-1, which is the freshest sample of raw oysters before freezing, showed little change until 4 months after storage, and their scores began to slowly decrease after 4 months of storage and still could be accepted (scores of more than 6.0) at the end of storage. Sensory evaluation scores on color, taste and odor of S-7 after 8 months of storage showed unacceptable score of 6 or less, and fishy and sour taste were slightly stronger at 12 months of storage. These results indicate that raw oysters with TVB-N and PV of 3.9 mg/100 g and 4.2 meq/kg can maintain oyster quality for more than one year at -20°C. On the other hand, it is suggested that raw oysters with TVB-N and PV of 15.2 mg N/100 g and 17.5 meq/kg may not be stored for more than 8 months at -20°C.

Microbiological Quality and Prevalence of β-Lactam Antibiotic Resistance Genes in Oysters (Crassostrea rhizophorae)

The microbiological quality of oysters reflects the microbiological quality of their habitats because they are filter feeders. The objective of this study was to assess the bacterial composition of the edible oyster Crassostrea rhizophorae in urban and preserved estuaries. Particularly, we assessed the presence of pathogenic bacteria, investigated antibiotic susceptibility in bacterial isolates, and quantified β-lactam antibiotic resistance genes (blaTEM, blaSHV, and blaKPC) via quantitative PCR of oyster DNA. Our results detected total coliforms, Escherichia coli , and enterobacteria in the oysters from urban estuaries, which is indicative of poor water quality. In addition, our detection of the eaeA and stxA2 virulence genes in 16.7% of E. coli isolates from oysters from this region suggests the presence of multiantibiotic-resistant enteropathogenic and enterohemorrhagic E. coli strains. During periods of low precipitation, increased contamination by E. coli (in winter) and Vibrio parahaemolyticus (in autumn) was observed. In contrast, cultivated oysters inhabiting monitored farms in preserved areas had low levels of bacterial contamination, emphasizing that oyster culture monitoring enhances food quality and makes oysters fit for human consumption. Distinct antibiotic resistance profiles were observed in bacteria isolated from oysters collected from different areas, including resistance to β-lactam antibiotics. The presence of the blaTEM gene in 91.3% of oyster samples indicated that microorganisms in estuarine water conferred the capability to produce β-lactamase. To our knowledge, this is the first study to directly quantify and detect β-lactam antibiotic resistance genes in oysters. We believe our study provides baseline data for bacterial dynamics in estuarine oysters; such knowledge contributes to developing risk assessments to determine the associated hazards and consequences of consuming oysters from aquatic environments containing pathogenic bacteria that may possess antibiotic resistance genes.

Impact of Environment and Ontogeny on Relative Fecundity and Egg Quality of Female Oysters (Crassostrea virginica) from Four Sites in Northern Chesapeake Bay.

Resource allocation to reproduction is a primary physiological concern for individuals, and can vary with age, environment, or a combination of both factors. In this study we quantified the impact of environment and individual age on the reproductive output of female oysters Crassostrea virginica. We determined the relative fecundity, egg total lipid content, and overall and omega-3/omega-6 (ω3/ω6) fatty acid signatures (FAS) of eggs spawned by female oysters over a 2-year period (n = 32 and n = 64). Variation was quantified spatially and ontogenetically by sampling young and old oyster populations from two rivers in Chesapeake Bay, totaling four collection sites. During Year 1, when oysters underwent oogenesis in different locations, overall and ω3/ω6 egg FAS varied significantly by river, with no significant differences observed in the FAS of oysters by age in Year 1. In Year 2, when oysters from different sites underwent oogenesis in a single location, no significant differences in the overall egg FAS or ω3/ω6 egg FAS by river or age were observed. These findings suggest that oysters integrate environment into their reproductive output, but that time spent growing at a specific location (in this case, represented by oyster age) plays a relatively minor role in the biochemical composition of oyster eggs. These results have consequences for our understanding of how resources are allocated from the female oyster to eggs and, more generally, the impact of environment and ontogeny on reproductive physiology.

Predictive modeling of European flat oyster (Ostrea edulis L.) fatty acid composition

This study investigates polyunsaturated fatty acids (PUFAs) of European flat oyster (Ostrea edulis L.) and their composition shift in relation to the interaction of selected factors in the marine environment of the Adriatic Sea, over an annual farming cycle. We advance the hypothesis that fatty acid composition may be predicted regarding the changes of abiotic environment parameters. Novel approach was developed as a tool for interpretation of PUFA ratio using mathematical models and algorithms, providing association and better prediction of observed variables compared to standard statistical techniques. Data analysis using R language package resulted in models that primarily provide the possibility to predict the PUFA value based on certain fluctuations in the environment. In addition to predictions, results present a useful tool for insight into the oysters’ quality and understanding of their basic biology in different environments. This is the first report of using mathematical modeling to investigate interactions between PUFA compositions of oyster meat relative to interactions of particular environmental variables. We furthermore discuss the potential of environmental variables in affecting the oyster PUFA composition and apply an approach providing a better insight into the health status and quality of oysters throughout the season. Model projection showed a nonlinear, parabolic dependence between the tested variables and dissolved oxygen. Both, the n-3 PUFA and DHA alone, were associated with an open-down parabolic relationship; the maximum levels were reached by 95 % oxygen saturation. The n-3 PUFAs and n-3/n-6 ratio were likely negatively affected by increase in sea water temperature, where a 15 % reduction in n-3 PUFAs content and 50 % reduction in n-3/n-6 proportion were predicted. Also, we detected FA ratios (AA/DHA, AA/EPA) and AA positively affected by increase in sulphate concentration and dissolved oxygen, respectively, and strongly negative prediction of ammonia level and sea water pH with AA, DHA and ARA/EPA ratio, respectively. These models might be applied to other aquatic species, for promotion of sea food quality, improvement of farming conditions and production, as well as for optimizing conditions in controlled trails.

Quantification of Vibrio species in oysters from the Gulf of Mexico with two procedures based on MPN and PCR

Oysters can accumulate potentially pathogenic water bacteria. The objective of this study was to compare two procedures to quantify Vibrio species present in oysters to determine the most sensitive method. We analyzed oyster samples from the Gulf of Mexico, commercialized in Mexico City. The samples were inoculated in tubes with alkaline peptone water (APW), based on three tubes and four dilutions (10-1 to 10-4). From these tubes, the first quantification of Vibrio species was performed (most probable number (MPN) from tubes) and bacteria were inoculated by streaking on thiosulfate-citrate-bile salts-sucrose (TCBS) petri dishes. Colonies were isolated for a second quantification (MPN from dishes). Polymerase chain reaction (PCR) was used to determine species with specific primers: ompW for Vibrio cholerae, tlh for Vibrio parahaemolyticus, and VvhA for Vibrio vulnificus. Simultaneously, the sanitary quality of oysters was determined. The quantification of V. parahaemolyticus was significantly higher in APW tubes than in TCBS dishes. Regarding V. vulnificus counts, the differences among both approaches were not significant. In contrast, the MPNs of V. cholerae obtained from dishes were higher than from tubes. The quantification of MPNs through PCR of V. parahaemolyticus and V. vulnificus obtained from APW was sensitive and recommendable for the detection of both species. In contrast, to quantify V. cholerae, it was necessary to isolate colonies on TCBS prior PCR. Culturing in APW at 42°C could be an alternative to avoid colony isolation. The MPNs of V. cholerae from dishes was associated with the bad sanitary quality of the samples.

The effect of a novel photodynamic activation method mediated by curcumin on oyster shelf life and quality

In this paper, the effect of photodynamic method mediated by curcumin (PDT) on the shelf life and quality of pacific oysters during storage at 5±1°C were analyzed. In our previous study we investigated the optimal treatment conditions of photodynamic method mediated by curcumin to sterilization were 10uM photosensitizer concentration and 5.4J/cm2 light energy density. Under these conditions, the effect of a novel photodynamic activation method mediated by curcumin on oyster shelf life and quality was researched. The total bacterial counts, TVB-N content and sensory analysis were used to evaluate the effects on oyster shelf life. The oyster shelf life was prolonged from 8days to 12days after photodynamic treatment and the oysters in the treatment group displayed notable odor retention, produced fewer odor corrupting substances when the control group oysters reached the end of their shelf life (day 8). Texture, free amino acid contents and fatty acid levels were applied to estimate the quality of the treated oysters. The texture had no significant change after treated with PDT. At the end of oyster shelf life, compared PDT group (PDT) with control group (control), total free amino acid contents (control: 234.30mg/100g, PDT: 813.02mg/100g) was higher and free fatty acid levels (control: 0.071mEq/L, PDT: 0.0455mEq/L) displayed lower in PDT group. This indicated that the treated oysters oxidized minimally, decayed slowly, decomposed fewer nutrients and had lower metabolic levels of spoilage microorganisms. PDT has a positive effect on prolonging oyster shelf life and its quality.

Quantitative quality evaluation of Eastern oyster (Crassostrea virginica) cultured by two different methods

In order to evaluate the quality of oysters and whether a production method affects quality or not, a set of objective quantitative quality measures was developed. Eastern oysters (Crassostrea virginica) were cultured using two different treatments (never desiccated or desiccated daily with tidal exposure) and the meats were tested by textural, physico-chemical and chemical analyses over a 25-day cold storage period. Texture analyses parameters (cutting force and chewiness on oyster adductor muscles) were strongly correlated with storage time before the death of oysters and could be used as a quality indicator for oyster. Total volatile basic nitrogen (TVBN) could be used as freshness indicator for raw Eastern oysters, with the acceptability of 11 mg/100 g. Models for evaluating the quality of oysters were established that reflect the impact of a biofouling treatment on oyster's shelf life and texture attributes. The methods and quality indicators developed in this study were effective in evaluating the quality and freshness of Eastern oysters objectively, and could serve as routine quality check of oyster meat for the industry.

Effects of High Hydrostatic Pressure on the Physical, Microbial, and Chemical Attributes of Oysters (Crassostrea virginica).

The change in the quality attributes (physical, microbial, and chemical) of oysters (Crassostrea virginica) after high hydrostatic pressure (HHP) treatment at 300 MPa at room temperature (RT, 25 °C) 300, 450, and 500 MPa at 0 °C for 2 min and control oysters without treatment were evaluated over 3 wk. The texture and tissue yield percentages of oysters HHP treated at 300 MPa, RT increased significantly (P < 0.05) compared to control. Aerobic and psychrotrophic bacteria in control oysters reached the spoilage point of 7 log CFU/g after 15 d. Coliform counts (log MPN/g) were low during storage with total and fecal coliforms less than 3.5 and 1.0. High pressure treated oysters at 500 MPa at 0 °C were significantly higher (P < 0.05) than oysters HHP treated at 300 MPa at 0 °C in lipid oxidation values. The highest pressure (500 MPa) treatment in this study, significantly (P < 0.05) decreased unsaturated fatty acid percentage compared to control. The glycogen content of control oysters at 3 wk was significantly higher (P < 0.05) when compared to HHP treated oysters [300 MPa, (RT); 450 MPa (0 °C); and 500 MPa (0 °C)]. HHP treatments of oysters were not significantly different in pH, percent salt extractable protein (SEP), and total lipid values compared to control. Based on our results, HHP prolongs the physical, microbial, and chemical quality of oysters.