Improved Microbial Safety of Direct Ozone-Depurated Shellstock Eastern Oysters (Crassostrea virginica) by Superchilled Storage

Bactericidal effect of water-washing methods on Vibrio vulnificus contaminated in a raw fish Konosirus punctatus: water type, temperature, and pH

This study aimed to evaluate a method for effectively reducing Vibrio vulnificus contamination in fish based on the type of washing water and method. Texture profiles and sensory evaluations were performed to determine the effect of the developed method on the quality and preference of the samples. The selected fish sample was Konosirus punctatus, which is mainly consumed in Asian countries. Various factors that could affect the survival rate of V. vulnificus were reviewed, including water type, temperature, exposure time, organic acids, pH, and washing methods. As a result, immersion and washing with filtered water with pH adjusted to 4.0 using acetic acid showed a high bactericidal effect of 2.5 log MPN/100 g. Furthermore, this method showed no statistically significant effect on the texture and sensory characteristics of fish. The results of the present study suggest a simple and effective method for preventing V. vulnificus infection in raw fish.

Effect of Neutral Protease on Freshness Quality of Shucked Pacific Oysters at Different Storage Conditions

The aim of this study was to investigate the effect of neutral protease treatment on the biochemical properties of various parts of Pacific oysters (Crassostrea gigas) under different storage conditions. The mechanism of quality degradation in the mantle, adductor muscle, gill, and trunk of treated oysters stored at -1.5 °C (superchilling) or 4 °C (refrigeration) for several days using different storage methods was studied. The results showed that the oyster treated with the enzyme exhibited higher glycogen content, flavor nucleotide content, and sensory scores compared to the control group. Superchilling at -1.5 °C was observed to slow the increase in total volatile basic nitrogen (TVB-N), total viable count (TVC), and pH, while maintaining sensory scores better than refrigeration at 4 °C. Both wet superchilling (WS) and dry exposed superchilling (DeS) methods effectively preserved freshness and quality at -1.5 °C. The freshness of the oysters' body trunk changed most significantly. K value, K' value, and AEC value, as the evaluation indexes of oyster freshness, were affected by the storage medium. Therefore, neutral protease enhances the flavor of oysters in a short time, and oysters stored in wet superchilling or dry exposed superchilling conditions have an extended shelf life.

Strategies to improve the postharvest management of flat oyster (Ostrea edulis) from aquaculture using the short-term storage and package in an innovative closed-circuit system

This study aimed to improve postharvest management of flat oysters reared in a longline system in the mid Adriatic Sea, using short-term storage and package in an innovative closed-circuit system. For the trial, 870 oysters were employed, divided into three experimental groups (A, B, and C), N = 270 oysters each group, whereas the remaining 60 oysters were used for the 2 controls. Each group differed in relation to the time spent in the depuration tank and the time of packaging: group A was packed and immediately transferred to the cell; group B was depurated in a tank for 48 h, then packed and transferred to the cell; group C was depurated in a tank for 48 h and then packed, depurated for another 24 h and transferred to a cell. Samples of each group were sampled at different times of permanence in cell (t0) up until 12 days (t12) for biomorphometric, sensorial, nutritional, and microbiological analysis. Although the nutritional and sensorial quality of the oysters was more pronounced in group A, B and C groups also showed good results. In these two groups, thanks to the use of the modern water recirculation system the quality and safety of oysters was improved by reducing the presence of sludge and eliminating fecal contaminants completely than A treatment and seawater control. These results were also confirmed by the tank control, where a more extended depuration period positively influenced the same parameters emphasizing the importance of the adequate depuration processes in oyster production.

Ozone application in different industries: A review of recent developments

Ozone - a powerful antimicrobial agent, has been extensively applied for decontamination purposes in several industries (including food, water treatment, pharmaceuticals, textiles, healthcare, and the medical sectors). The advent of the COVID-19 pandemic has led to recent developments in the deployment of different ozone-based technologies for the decontamination of surfaces, materials and indoor environments. The pandemic has also highlighted the therapeutic potential of ozone for the treatment of COVID-19 patients, with astonishing results observed. The key objective of this review is to summarize recent advances in the utilisation of ozone for decontamination applications in the above-listed industries while emphasising the impact of key parameters affecting microbial reduction efficiency and ozone stability for prolonged action. We realise that aqueous ozonation has received higher research attention, compared to the gaseous application of ozone. This can be attributed to the fact that water treatment represents one of its earliest applications. Furthermore, the application of gaseous ozone for personal protective equipment (PPE) and medical device disinfection has not received a significant number of contributions compared to other applications. This presents a challenge for which the correct application of ozonation can mitigate. In this review, a critical discussion of these challenges is presented, as well as key knowledge gaps and open research problems/opportunities.

Effects of Individual and Block Freezing on the Quality of Pacific Oyster (Crassostrea gigas) during Storage under Different Pretreatment Conditions

In this study, a series of pretreatments, including ice-glazing, polyphosphate impregnated, and both ice-glazing and polyphosphate impregnated, were employed to pretreat shucked oysters in order to explore the optimal processing conditions for long-time storage. The effect of repeated freezing-thawing cycles on the quality of oysters was evaluated. Several quality indicators were used to investigate the effects of pretreatment. For the VBN (volatile salt-based nitrogen) value, the lowest value was 9.1 ± 0.2 of BPG (block oyster with polyphosphate impregnated and ice-glazing), which was significantly lower than 9.6 ± 0.2 of IPG (individual oyster with polyphosphate impregnated and ice-glazing). In terms of drip loss, there was no significant difference between the IPG (21.0 ± 0.2%) and the BPG (20.8 ± 0.2%). In addition, the highest WHC% (water holding capacity) was IPG (65.5 ± 0.5%) which was slightly lower than BPG (67.6 ± 0.6%). As compared to the experimental control, the IPG and BPG had the best appearance and color. In terms of TAPC (total aerobic plate count), with the increase of freezing storage time, each group showed a slight downward trend, but the difference was not statistically significant. After repeated freezing-thawing of block frozen oysters, there were significant differences in drip loss, WHC, and cooked taste with the increasing number of times, and there was a trend of deterioration (p < 0.05). Repeated freezing and thawing can seriously degrade the quality of oysters, so individual freezing (especially IPG) should be the most appropriate processing method.

Depuration of live oysters to reduce Vibrio parahaemolyticus and Vibrio vulnificus: A review of ecology and processing parameters

Consumption of raw oysters, whether wild-caught or aquacultured, may increase health risks for humans. Vibrio vulnificus and Vibrio parahaemolyticus are two potentially pathogenic bacteria that can be concentrated in oysters during filter feeding. As Vibrio abundance increases in coastal waters worldwide, ingesting raw oysters contaminated with V. vulnificus and V. parahaemolyticus can possibly result in human illness and death in susceptible individuals. Depuration is a postharvest processing method that maintains oyster viability while they filter clean salt water that either continuously flows through a holding tank or is recirculated and replenished periodically. This process can reduce endogenous bacteria, including coliforms, thus providing a safer, live oyster product for human consumption; however, depuration of Vibrios has presented challenges. When considering the difficulty of removing endogenous Vibrios in oysters, a more standardized framework of effective depuration parameters is needed. Understanding Vibrio ecology and its relation to certain depuration parameters could help optimize the process for the reduction of Vibrio. In the past, researchers have manipulated key depuration parameters like depuration processing time, water salinity, water temperature, and water flow rate and explored the use of processing additives to enhance disinfection in oysters. In summation, depuration processing from 4 to 6 days, low temperature, high salinity, and flowing water effectively reduced V. vulnificus and V. parahaemolyticus in live oysters. This review aims to emphasize trends among the results of these past works and provide suggestions for future oyster depuration studies.

Advances, Applications, and Comparison of Thermal (Pasteurization, Sterilization, and Aseptic Packaging) against Non-Thermal (Ultrasounds, UV Radiation, Ozonation, High Hydrostatic Pressure) Technologies in Food Processing

Nowadays, food treatment technologies are constantly evolving due to an increasing demand for healthier and tastier food with longer shelf lives. In this review, our aim is to highlight the advantages and disadvantages of some of the most exploited industrial techniques for food processing and microorganism deactivation, dividing them into those that exploit high temperatures (pasteurization, sterilization, aseptic packaging) and those that operate thanks to their inherent chemical–physical principles (ultrasound, ultraviolet radiation, ozonation, high hydrostatic pressure). The traditional thermal methods can reduce the number of pathogenic microorganisms to safe levels, but non-thermal technologies can also reduce or remove the adverse effects that occur using high temperatures. In the case of ultrasound, which inactivates pathogens, recent advances in food treatment are reported. Throughout the text, novel discoveries of the last decade are presented, and non-thermal methods have been demonstrated to be more attractive for processing a huge variety of foods. Preserving the quality and nutritional values of the product itself and at the same time reducing bacteria and extending shelf life are the primary targets of conscious producers, and with non-thermal technologies, they are increasingly possible.

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.

Occurrence, antibiotic-resistance and virulence of E. coli strains isolated from mangrove oysters (Crassostrea gasar) farmed in estuaries of Amazonia

Concentration of bacterial species indicative of fecal contamination in the gut of mangrove oysters (Crassostrea gasar) is a major concern for public health and food surveillance. Our work aimed to determine the occurrence, antibiotic-resistance, phylogenetic profile and virulence of Escherichia coli strains isolated from C. gasar farmed in four estuaries of Amazonia. Santo Antônio de Urindeua was the sampling point with the highest number of E. coli cells in oyster samples (10⁴ per 100 g of sample). Twenty-four isolates (52.2%) showed resistance to cephalotin and 18 to amoxicillin (39.1%). Eighteen clonal populations were determined by rep-PCR and were mainly affiliated to the pathogenic and commensal phylo-groups B1 and D. The presence of elt genes suggests that 10 of these clones belong to the Enterotoxigenic Escherichia coli pathotype. Plasmids, mostly of the F incompatibility group, were detected in the majority of the strains. All isolates were susceptible to last-resort antibiotics.

Comparative Survival and the Cold-Induced Gene Expression of Pathogenic and Nonpathogenic Vibrio Parahaemolyticus from Tropical Eastern Oysters during Cold Storage

Expression of the regulatory stress rpoS gene controls the transcription of cspA genes, which are involved in survival and adaptation to low temperatures. The purpose of this study was to assess the growth kinetics of naturally occurring V. parahaemolyticus in shellstock oysters and in vitro and the cold-shock-induced expression of the rpoS and cspA gene response in vitro during postharvest refrigeration. Naturally contaminated eastern oysters (Crassostrea virginica) and pathogenic (Vp-tdh) and nonpathogenic (Vp-tlh) isolates were stored at 7 ± 1 °C for 168 h and 216 h, respectively. The regulatory stress (rpos) and cold-shock (cspA) gene expressions were determined by reverse transcription PCR. At 24 h, the (Vp-tdh) strain grew faster (p < 0.05) than the (Vp-tlh) strain in oysters (λ = 0.33, 0.39, respectively) and in vitro (λ = 0.89, 37.65, respectively), indicating a better adaptation to cold shock for the (Vp-tdh) strain in live oysters and in vitro. At 24 h, the (Vp-tdh) strain rpoS and cspA gene expressions were upregulated by 1.9 and 2.3-fold, respectively, but the (Vp-tlh) strain rpoS and cspA gene expressions were repressed and upregulated by -0.024 and 1.9-fold, respectively. The V. parahaemolyticus strains that were isolated from tropical oysters have adaptive expression changes to survive and grow at 7 °C, according to their virulence.