Inactivation of Vibrio parahaemolyticus and Vibrio vulnificus in oysters by high-hydrostatic pressure and mild heat

Several recent outbreaks associated with oysters have heightened safety concerns of raw shellfish consumptions, with the majority being attributed to Vibrio spp. The objective of this study was to determine the effect of high-hydrostatic pressure (HHP) followed by mild heating on the inactivation of Vibrio parahaemolyticus and Vibrio vulnificus in live oysters. Inoculated oysters were randomly subjected to: a) pressurization at 200–300 MPa for 2 min at 21 °C, b) mild heat treatment at 40, 45 or 50 °C for up to 20 min and c) pressure treatment of 200–300 MPa for 2 min at 21 °C followed by heat treatment at 40–50 °C. Counts of V. parahaemolyticus and V. vulnificus were then determined using the most probable number (MPN) method. Pressurization at 200–300 MPa for 2 min resulted in various degrees of inactivation, from 1.2 to >7 log MPN/g reductions. Heat treatment at 40 and 45 °C for 20 min only reduced V. parahaemolyticus and V. vulnificus by 0.7–2.5 log MPN/g while at 50 °C for 15 min achieved >7 log MPN/g reduction. HHP and mild heat had synergistic effects. Combinations such as HHP at 250 MPa for 2 min followed by heat treatment at 45 °C for 15 min and HHP at 200 MPa for 2 min followed by heat treatment at 50 °C for 5 min reduced both V. parahaemolyticus and V. vulnificus to non-detectable levels by the MPN method (<3 MPN/g). HHP at ≥275 MPa for 2 min followed by heat treatment at 45 °C for 20 min and HHP at ≥200 MPa for 2 min followed by heat treatment at 50 °C for 15 min completely eliminated both pathogens in oysters (negative enrichment results). This study demonstrated the efficiency of HHP followed by mild heat treatments on inactivation of V. parahaemolyticus and V. vulnificus and could help the industry to establish parameters for processing oysters.     

Temperature Effects on the Depuration of Vibrio parahaemolyticus and Vibrio vulnificus from the American Oyster (Crassostrea virginica)

ABSTRACT:  This study investigated temperature effects on depuration for reducing Vibrio parahaemolyticus and Vibrio vulnificus in American oyster ( Crassostrea virginica ). Raw oysters were inoculated with 5-strain cocktail of V. parahaemolyticus or V. vulnificus to levels of 10⁴ to 10⁵ MPN (most probable number)/g and depurated in artificial seawater (ASW) at 22, 15, 10, and 5 °C. Depuration of oysters at 22 °C had limited effects on reducing V. parahaemolyticus or V. vulnificus in the oysters. Populations of V. parahaemolyticus and V. vulnificus were reduced by 1.2 and 2.0 log MPN/g, respectively, after 48 h of depuration at 22 °C. Decreasing water temperature to 15 °C increased the efficacy of depuration in reducing V. parahaemolyticus and V. vulnificus in oysters. Reductions of V. parahaemolyticus and V. vulnificus in oysters increased to 2.1 and 2.9 log MPN/g, respectively, after 48 h of depuration at 15 °C. However, depurations at 10 and 5 °C were less effective than at 15 °C in reducing the Vibrio spp. in oysters. Extended depuration at 15 °C for 96 h increased reductions of V. parahaemolyticus and V. vulnificus in oysters to 2.6 and 3.3 log MPN/g, respectively.     

Validation of high pressure processing for inactivating Vibrio parahaemolyticus in Pacific oysters (Crassostrea gigas)

This study identified and validated high hydrostatic pressure processing (HPP) for achieving greater than 3.52-log reductions of Vibrio parahaemolyticus in the Pacific oysters (Crassostrea gigas) and determined shelf life of processed oysters stored at 5 °C or in ice. Raw Pacific oysters were inoculated with a clinical strain of V. parahaemolyticus 10293 (O1:K56) to levels of 10^4-5 cells per gram and processed at 293 MPa (43 K PSI) for 90, 120, 150, 180 and 210 s. Populations of V. parahaemolyticus in oysters after processes were analyzed with the 5-tube most probable number (MPN) method. Negative results obtained by the MPN method were confirmed with a multiplex PCR detecting genes encoding thermolabile hemolysin (tl), thermostable direct hemolysin (tdh) and TDH-related hemolysin (trh). A HPP of 293 MPa for 120 s at groundwater temperature (8 ± 1 °C) was identified capable of achieving greater than 3.52-log reductions of V. parahaemolyticus in Pacific oysters. Oysters processed at 293 MPa for 120 s had a shelf life of 6-8 days when stored at 5 °C or 16-18 days when stored in ice. This HPP can be adopted by the shellfish industry as a post harvest process to eliminate V. parahaemolyticus in raw oysters.     

Effective reduction of Vibrio vulnificus in the Eastern oyster (Crassostrea virginica) using high salinity depuration

Depuration under different salinities was used to reduce the human pathogen Vibrio vulnificus from Eastern oysters (Crassostrea virginica). Individual recirculating systems were used to test the efficacy of depuration at three salinities (15, 25, and 35 psu) in four independent trials during a 14 day period. Initial loads of V. vulnificus were higher than 10,000 MPN/g of oyster meat in all trials. Data showed that 25 and 35 psu treatments were more efficient in reducing V. vulnificus numbers than 15 psu with an overall reduction of >3 logs. A significant decrease in MPN/g was observed as early as day 6 and further reductions were observed at day 10, while longer depurations did not improve efficacy. Only the highest salinity (35 psu) was capable of reducing V. vulnificus numbers to the FDA recommended level of <30 MPN/g in two of the four trials. Oysters survived well in the depuration systems with minimal mortality (<1%) but their condition index (meat quality and yield) decreased during the 14 day period in all treatments. The data presented in this study suggests that high salinity depuration is a promising method to reduce V. vulnificus in oysters.     

Occurrence and distribution of Vibrio parahaemolyticus in retail oysters in Sao Paulo State, Brazil

Vibrio parahaemolyticus is a potentially pathogenic bacterium that occurs naturally in estuarine environments worldwide, and is often associated with gastroenteritis in humans following consumption of raw bivalve mollusks, especially raw oysters. The occurrence of total and pathogenic V. parahaemolyticus in 74 samples of raw oysters collected in restaurants, supermarkets, groceries and beach huts in Sao Paulo State, was monitored between February 2006 and January 2007. Enumeration of V. parahaemolyticus was performed according to the most probable number (MPN) procedure. Five to ten typical colonies were selected from thiosulfate-citrate-bile salts-sucrose (TCBS) agar plates for confirmation by the presence of the species-specific gene tlh and the virulence genes tdh and trh by multiplex PCR. V. parahaemolyticus was detected in 100% of samples. The densities of total V. parahaemolyticus varied from 1.78 to 6.04 log₁₀ (MPN/g), with higher densities being detected in fall and summer, and lower densities in winter (P < 0.05). There was no statistical difference among densities of V parahaemolyticus regarding the site of collection. None of the 1943 V. parahaemolyticus isolates contained tdh and/or trh. These data provide information for the assessment of exposure to V. parahaemolyticus in oysters consumed in Sao Paulo, State, Brazil.     

Comparison of molecular detection methods for Vibrio parahaemolyticus and Vibrio vulnificus

Pathogenic vibrios are a global concern for seafood safety and many molecular methods have been developed for their detection. This study compares several molecular methods for detection of total and pathogenic Vibrio parahaemolyticus and Vibrio vulnificus, in MPN enrichments from oysters and fish intestine samples. This study employed the DuPont Qualicon BAX^® System Real-Time PCR assay for detection of V. parahaemolyticus and V. vulnificus. Multiplex real-time PCR detection of total (tlh+), tdh+, and trh+ V. parahaemolyticus was conducted on the Cepheid SmartCycler II. Total (rpoD) and tdh+ V. parahaemolyticus were also detected using LAMP. V. vulnificus detection was performed using real-time PCR methods developed for the SmartCycler and the AB 7500 Fast. Recommended template preparations were compared to BAX^® lysis samples for suitability. There was no significant difference in detection of V. parahaemolyticus and V. vulnificus using the BAX^® or SmartCycler assays. The AB assay showed no difference from other methods in detection of V. vulnificus unless boiled templates were utilized. There was a significant difference in detection of tdh+ V. parahaemolyticus between SmartCycler and LAMP assays unless the total (tlh+) V. parahaemolyticus gene target was omitted from the SmartCycler assay; a similar trend was observed for trh+ V. parahaemolyticus.     

Behavior and incidence of Vibro parahaemolyticus in Sydney rock oysters (Crassostrea commercialis)

Vibrio parahaemolyticus grew poorly or not at all during storage of unopened Sydney rock oysters (Crassostrea commercialis) at 15 and 30°C for 2 and 7 days. Although V. parahaemolyticus counts often increased at 30°C, counts above 10⁴/g were not observed. Escherichia coli counts did not usually change substantially under these conditions. V. parahaemolyticus grew more readily during storage of unopened oysters under more severe conditions, with counts approaching or exceeding 10⁶/g after continuous or intermittent storage at 37°C. Opened oysters provided a much more favourable environment than unopened oysters for growth of V. parahaemolyticus. Growth occurred at 15, 30 and 37°C, with counts > 10⁶/g after overnight storage at 30 or 37°C. A survey of 30 market samples of oysters was conducted. Sixteen samples of unopened oysters were collected at the wholesale level and 14 samples of refrigerated opened oysters were purchased from retailers. V. parahaemolyticus was present in all samples of unopened oysters (range 0.4/g?2.3 × 10⁴/g) and in 13 samples of opened oysters (range 4.3/g? > 1.1 × 10³/g).     

Vibrio parahaemolyticus in granulated ark shell clam (Tegillarca granosas): accumulation from water and survival during cold storage and thermal process

This study investigated accumulation of Vibrio parahaemolyticus in granulated ark shell clam (Tegillarca granosas) exposed to contaminated water and survival of V. parahaemolyticus in the clams during cold storage and heating processes. Vibrio parahaemolyticus could be accumulated in clams to a level similar to that of contaminated water within 12 h of exposure of clams to contaminated water at temperatures between 9 and 33 °C. Keeping clams stored at 5 and 0 °C for 10 days resulted in 1.98 and 2.32 log MPN g^?1 reductions of V. parahaemolyticus, respectively, in the clams. Frozen storage at ?18 °C for 15 days or at ?30 °C for 30 days were capable of reducing V. parahaemolyticus from 4.05 log MPN g^?1 to non‐detectable levels (< 3 MPN g^?1). A heating process in hot water at 80 °C or higher for 1 min also reduced V. parahaemolyticus in the clams to non‐detectable levels.     

High Salinity Relaying to Reduce Vibrio parahaemolyticus and Vibrio vulnificus in Chesapeake Bay Oysters (Crassostrea virginica)

Cases of Vibrio infections in the United States have tripled from 1996 to 2009 and these infections are most often associated with the consumption of seafood, particularly oysters (Crassostrea virginica). Information is needed on how to reduce numbers of Vibrio parahaemolyticus and Vibrio vulnificus in bi‐valve molluscan shellfish (for example, oysters). The purpose of this study was to evaluate the effectiveness of high salinity relaying or treatment in recirculating aquaculture systems (RASs) as methods to reduce the abundance of V. parahaemolyticus and V. vulnificus in oysters. For relaying field trials, oysters were collected from approved harvest waters, temperature abused outside under a tarp for 4 h, and then transferred to high (29 to 33 ppt.) and moderate (12 to 19 ppt.) salinities. For RAS treatment trial, oysters were transferred to 32 to 34 ppt. salinity at 15 °C. After 7, 14, 21, and in some instances 28 d, oysters were collected and analyzed for V. parahaemolyticus and V. vulnificus levels using multiplex real‐time PCR. Initial levels of V. parahaemolyticus and V. vulnificus ranged from 3.70 to 5.64 log₁₀ MPN/g, and were reduced by 2 to 5 logs after 21 to 28 d in high salinity water (29 to 34 ppt.). Oyster mortalities averaged 4% or less, and did not exceed 7%. Relaying of oysters to high salinity field sites or transfer to high salinity RAS tanks was more effective in reducing V. vulnificus compared with V. parahaemolyticus. These results suggest that high salinity relaying of oysters is more effective in reducing V. vulnificus than V. parahaemolyticus in the oyster species used in this study.     

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.     

Depuration of Oysters (Crassostrea gigas) Contaminated with Vibrio parahaemolyticus and Vibrio vulnificus with UV Light and Chlorinated Seawater

The efficacy of depuration using UV light and chlorinated seawater for decontaminating Vibrio parahaemolyticus and Vibrio vulnificus from oysters was investigated. Oysters were contaminated with a five-strain cocktail of V. parahaemolyticus or V. vulnificus to levels of 10(4) to 10(5) CFU ml(-1) for bioaccumulation. The depuration was conducted in a closed system in which 350 liters of seawater was recirculated at a rate of 7 liters/min for 48 h at room temperature. Counts of V. parahaemolyticus or V. vulnificus were determined at 0, 6, 18, 24, and 48 h. Three treatments were conducted: T1, control treatment; T2, UV treatment; and T3, UV plus chlorine treatment. After 48 h of depuration of V. parahaemolyticus, T3 reduced the count by 3.1 log most probable number (MPN) g(-1) and T2 reduced the count by 2.4 log MPN g(-1), while T1 reduced the count by only 2.0 log MPN g(-1). After 48 h of depuration of V. vulnificus, T2 and T3 were efficient, reducing the counts by 2.5 and 2.4 log MPN g(-1), respectively, while T1 reduced the count by only 1.4 log MPN g(-1). The UV light plus chlorine treatment was more efficient for controlling V. parahaemolyticus in oysters. Both UV light and UV light plus chlorine were efficient for V. vulnificus. The present study is the first report showing the efficacy of depuration systems for decontaminating V. parahaemolyticus and V. vulnificus in oysters cultivated on the Brazilian coast. This study provides information on processes that can contribute to controlling and preventing such microorganisms in oysters and could be used for effective postharvest treatment by restaurants and small producers of oysters on the coast of Brazil.     

Effect of crust freezing applied alone and in combination with ultraviolet light on the survival of Campylobacter on raw chicken

The application of crust freezing (CF) applied as a stand-alone treatment or in combination with ultraviolet (UV) light for reducing the level of artificially inoculated Campylobacter jejuni on raw chicken was investigated. CF air temperatures of −5, −15 and −27 °C (±3 °C) with freezing times of 70, 15 and 6 min, respectively, were used. The level of C. jejuni on chicken was also examined following subsequent refrigerated (0–4 °C) storage at 3 and 7 days. All CF treatments resulted in significant reductions compared to untreated controls (P < 0.05). Although combining CF with UV also resulted in significant reductions for C. jejuni, the combined treatments were generally no more effective than treatment by CF alone. Overall, the color of chicken drumsticks was not affected by CF treatments (P ≥ 0.05). In general, CF resulted in increased drip loss (P < 0.05), which increased over storage time and was greater at higher CF temperatures. The current study indicates that CF has potential for reducing the levels of C. jejuni by between 0.5 and 1.5 log₁₀ CFU/g and impacts minimally on the color of treated skin.     

Occurrence of Vibrio parahaemolyticus in Two Oregon Oyster-growing Bays

ABSTRACT: Occurrence of Vibrio parahaemolyticus in 2 Oregon oyster-growing areas (Yaquina andTillamook Bays) was studied from November 2002 to October 2003. Vibrio parahaemolyticus was detected in 15.0% of oyster, 20.0% of seawater, and 47.5% of sediment samples with very low levels of pathogenic strains being detected in oysters (≤3.6 most probable number [MPN] /g). The densities of total and pathogenic V. parahaemolyticus were higher in sediment (≤1100 and ≤43 MPN/g) than in seawater (≤15 and ≤3.6 MPN/100 mL) or oyster (≤43 and ≤3.6 MPN/ g). Densities of V. parahaemolyticus in both bays were positively correlated to water temperatures ( P < 0.01), with higher densities in samples being detected in summer, especially July and August. There was no correlation between the densities of V. parahaemolyticus and water salinity or the densities of V. parahaemolyticus and bacterial populations in seawater. Freshly harvested oysters should be kept at refrigeration temperatures to prevent rapid growth of pathogenic V. parahaemolyticus in contaminated oysters.     

Microbiological quality of ice creams commercialized in some cities in the state of Rio de Janeiro, Brazil

The microbiological quality of 60 ice cream samples of three commercial brands (A, B and C) of various flavours, commercialized in some towns in the State of Rio de Janeiro, Brazil, was evaluated. Total bacteria count (TCB), coliforms at 35°C (CT), coliforms at 44°C (CF) and presence of Staphylococcus aureus were performed on all samples. TCB ranged from 2.0 × 10 ² to 6.9 × 10 ⁵ cfu/mL, CT from < 3–≥ 2400 MPN/mL, CF from < 3–1100 MPN/mL and S. aureus from < 10–1.4 × 10 ⁶ cfu/mL. The level of bacterial contamination found in this study reflects the unhygienic conditions prevalent in manufacturing and storage of ice creams. Actions are thus necessary by the Brazilian regulatory agencies to require the ice cream processing plants to adopt quality guarantee systems, such as good manufacturing practices and hazard analysis and critical control points system.     

Bacterial spore inactivation at 45-65 °C using high pressure processing: Study of Alicyclobacillus acidoterrestris in orange juice

High pressure processing (HPP) is a new non-thermal technology commercially used to pasteurize fruit juices and extend shelf-life, while preserving delicate aromas/flavours and bioactive constituents. Given the spoilage incidents and economic losses due to Alicyclobacillus acidoterrestris in the fruit juice industry, the use of high pressure (200 MPa – 600 MPa) in combination with mild temperature (45 °C–65 °C) for 1–15 min, to inactivate these spores in orange juice were investigated. As expected, the higher the temperature, pressure and time, the larger was the A. acidoterrestris inactivation. The survival curves were described by the first order Bigelow model. For 200 MPa, D_45 °C = 43.9 min, D_55 °C = 28.8 min, D_65 °C = 5.0 min and z-value = 21.3 °C. At 600 MPa, D_45 °C = 12.9 min, D_55 °C = 7.0 min, D_65 °C = 3.4 min and z-value = 34.4 °C. Spores were inactivated at 45 °C and 600 MPa, and at 65 °C only 200 MPa was needed to achieve reduction in spore numbers.     

Total and pathogenic Vibrio parahaemolyticus in shrimp: Fast and reliable quantification by real-time PCR

Vibrio parahaemolyticus is found in aquatic environments and is the leading cause of gastroenteritis due to seafood consumption worldwide. We evaluated a quantitative real-time PCR (Q-PCR) assay with hydrolysis probes, to determine whether this method could be used for the efficient counting of total, tdh and trh-positive V. parahaemolyticus in shrimps. We assessed the specificity of this assay, using 62 strains from 12 non target bacterial species of the Vibrio, Photobacterium, Shewanella and Aeromonas genera. Only V. parahaemolyticus with the appropriate target gene generated a fluorescent signal. We assessed the robustness of this assay, by analyzing spiked shrimps by Q-PCR and traditional culture methods, using most probable number (MPN)-PCR. After a 6 h enrichment period, the assay successfully detected total and pathogenic V. parahaemolyticus in shrimps samples spiked with less than 5 V. parahaemolyticus cells/g of shrimp. The Q-PCR results obtained were compared with those obtained by most probable number (MPN)-PCR format. An excellent correlation between the two methods was observed in all cases (R² > 0.9742). The application of this Q-PCR assay to 85 natural shrimp samples also resulted in the successful quantification of V. parahaemolyticus in this matrix, and the counts obtained were correlated with those obtained by (MPN)-PCR (P = 0.2598). Thus, this rapid and sensitive Q-PCR can be used to quantify V. parahaemolyticus in natural shrimp samples. This assay could be proposed, in response to the demands of the European Commission, as a tool for testing for the presence of vibrios in crustaceans, making it possible to legislate in this domain.     

A survey of oysters (Crassostrea gigas) in New Zealand for Vibrio parahaemolyticus and Vibrio vulnificus

A microbiological survey was conducted to determine the levels of total and pathogenic Vibrio parahaemolyticus (Vp) and Vibrio vulnificus (Vv) in Pacific oysters (Crassostrea gigas) collected from commercial growing areas in the North Island, New Zealand.The survey was intended to be geographically representative of commercial growing areas of Pacific oysters in New Zealand, while selecting the time frame most likely to coincide with the increased abundance of pathogenic vibrio species. Vp was detected in 94.8% of oyster samples examined (n = 58) with a geometric mean concentration of 99.3 MPN/g, while Vv was detected in 17.2% of oyster samples examined with a geometric mean concentration of 7.4 MPN/g. The frequency of Vp positive samples was 1.7 fold greater than reported in a study conducted three decades ago in New Zealand. Potentially virulent (tdh positive) Vp was detected in two samples (3.4%, n = 58) while no trh (another virulence marker) positive samples were detected. 16 S rRNA genotype could be assigned only to 58.8% of Vv isolates (8:1:1 A:B:AB ratio, n = 10). There was a good agreement [98.2% of Vp (n = 280) and 94.4% of Vv (n = 18) isolates] between molecular tests and cultivation based techniques used to identify Vibrio isolates and there was a significant (R² = 0.95, P < 0.001, n = 18) linear relationship between the MPN estimates by real-time PCR and cultivation. There was no significant correlation between any of the environmental parameters tested and Vp or Vv concentrations.     

Optimization of pressure-induced germination of Bacillus sporothermodurans spores in water and milk

Bacillus sporothermodurans produces highly resistant endospores that can survive ultra-high-temperature treatment in milk. The induction of endospore germination before a heat treatment could be an efficient method to inactivate these bacteria and ensure milk sterility. In this work, the rate of spore germination of B. sporothermodurans LTIS27 was measured in distilled water after high-pressure treatments with varying pressure (50–600 MPa), treatment temperature (20–50 °C), pressure-holding time (5–30 min) and post-pressurization incubation time (30–120 min) at 37 °C or 4 °C. The results showed that pressure-induced germination was maximal (62%) after a treatment at 200 MPa and 20 °C and increased with pressure-holding time and post-pressurization incubation time. Treatment temperature had no significant effect on germination. A central composite experimental design with three factors (pressure, pressure-holding time, and post-pressurization incubation time) using response surface methodology was used to optimize the germination rate in distilled water and in skim milk. No factor interaction was observed. Germination was induced at lower pressure and was faster in milk than in distilled water, but complete germination was not reached. The optimum germination obtained with experimental data was 5.0 log cfu/mL in distilled water and 5.2 log cfu/mL in milk from 5.7 log cfu/mL of spores initially present in the suspension. This study shows the potential of using high hydrostatic pressure to induce the germination of B. sporothermodurans spores in milk before a heat treatment.     

Susceptibility of Vibrio parahaemolyticus to disinfectants after prior exposure to sublethal stress

In the present study, Vibrio parahaemolyticus 690 in phosphate buffered-saline containing 3% NaCl was subjected to sublethal stresses: heat shock at 42 °C for 15 min, acid adaptation at pH 5.0 for 30 min, or cold shock at 20 °C for 4 h. The effect of sublethal stress on the susceptibility of V. parahaemolyticus to a chlorine-containing disinfectant (Clidox-S) and a quaternary ammonium compound (Quatricide) at 25 and 40 °C was investigated. It was found that the sublethal stresses examined enhanced the resistance of V. parahaemolyticus 690 to both disinfectants. Depending on the kinds of sublethal stress, V. parahaemolyticus 690 showed various degrees of enhanced resistance to disinfectants. Furthermore, the phenomenon of enhanced resistance to the disinfectants was more marked at 40 than at 25 °C.     

The effect of high hydrostatic pressure on the microbiological quality and safety of carrot juice during refrigerated storage

The microbial quality of untreated and pressure-treated carrot juice was compared during storage at 4, 8 and 12 °C. High pressure treatment at 500 MPa and 600 MPa (1 min/20 °C) reduced the total counts by approximately 4 log CFU ml⁻¹ and there was very little growth of the survivors during storage at 4 °C for up to 22 days. Total counts increased during storage of pressure-treated juice at 8 °C and 12 °C but took significantly longer to reach maximum levels compared to the untreated juice. The microflora in the untreated juice consisted predominantly of Gram-negative bacteria, identified as mostly Pantoea spp., Erwinia spp. and Pseudomonas spp. Initially the pressure-treated juice contained low numbers of spore-forming bacteria (Bacillus spp. and Paenibacillus spp.) and Gram-positive cocci; the spore-formers continued to dominate during storage.