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. 2023 Sep 26;33(6):1495–1504. doi: 10.1007/s10068-023-01421-y

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

Seul-Ki Park 1,#, Daeun Lee 2,#, Du-Min Jo 2,3, Daeung Yu 4,5, Ho-Su Song 6, Young-Mog Kim 2,3,✉
PMCID: PMC10992113  PMID: 38585562

Abstract

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.

Keywords: The bactericidal effect, Water-washing, Vibrio vulnificus, Raw fish, Konosirus punctatus

Introduction

In summer, serious attention to the hygiene of seafood is required due to rising ocean temperatures. Various foodborne pathogenic bacteria are commonly detected in seafood. There is a high probability of exposure to pathogenic Vibrio spp. when seafood is consumed without cooking or heating. Vibrio vulnificus is a marine bacterium associated with foodborne diseases (Ali et al., 2020). V. vulnificus infection often causes fatal diseases, such as sepsis, in patients suffering from chronic liver disease, and those having weak immune system and wounded skin. Furthermore, sepsis from V. vulnificus can lead to death in severe cases (Liang et al., 2021). In particular, patients with chronic underlying diseases such as immunodeficiency, diabetes, and liver disease, classified as a high-risk group, can suffer from acute sepsis with a fatality rate of 50% (Bhat et al., 2019). In addition, these high-risk groups can suffer symptoms up to 80% more than healthy people (Sampaio et al., 2022). V. vulnificus is a halophilic and waterborne infectious strain whose growth is highly affected by environmental factors such as temperature, salinity, and pH. The conditions for viable growth of V. vulnificus are a temperature of 9–31 °C, salinity of 5–35%, and pH of 5–10 (DaSilva et al., 2012; Kang et al., 2020). Various studies have reported methods for reducing V. vulnificus contamination in seafood. Previous methods include UV treatment (Roy et al., 2021), vacuum packaging (Zhao et al., 2021), high pressure (Vu et al., 2018), electrolyzed water treatment (Palamae et al., 2023), irradiation (Park et al., 2018), ozone water (Hernández et al., 2018), and artificial depuration (Jeong et al., 2021). These studies have mostly focused on shellfish, including oysters, and very few studies have focused on fish. Previous methods, such as heat treatment, cause denaturation of fish protein.

Acid treatment is one of the most important methods for improving food stability and storage and is simple, fast, and inexpensive among the traditional food sterilization methods. Acetic, citric, and lactic acids have been designated as Generally Recognized as Safe (GRAS) by the US Food and Drug Administration (FDA) and are generally proven safe for direct use in foods (US FDA, 2019). Additionally, several studies have reported that organic acids are useful in anti-acidification, extending shelf life, and reducing gram-negative bacteria (Kovanda et al., 2019; Monirul et al., 2019). However, there have been very few studies on technologies that reduce V. vulnificus without changing the basic properties of the fish. Simple and effective technologies need to be developed for application in the seafood industry, traditional markets, restaurants, and households. Therefore, this study aimed to investigate the bactericidal effects of various factors such as water type, temperature, exposure time, types of organic acids, pH, cutting type, and physical wash on V. vulnificus in contaminated fish (Konosirus punctatus). Additionally, texture profile and sensory property analyses were performed to evaluate the effects of these factors on the quality of fish samples.

Materials and methods

Sample preparation and microorganisms

Live fish (Konosirus punctatus) were purchased from a traditional market located in Busan, South Korea, and used for experiments on the day of purchase. The sample was prepared according to three different cutting types, as shown in Fig. 1, and the process was performed immediately after purchase. The gills, viscera, and intestine were removed for the semi-dressed type; the head, tail, and fins were additionally removed from the semi-dressed type for the pan-dressed type; all bones were removed from the pan-dressed type for the boneless-fillet type (only meat remained). The weight of the fish sample used in the study ranged from 70 to 80 g, with an average weight was 74.5 ± 2.1 g. The average length of the fish sample before cutting was 15.4 ± 1.8 cm. The semi-dressed samples with the head attached (without caudal fin) had an average length of 13.1 ± 1.1 cm, while the pan-dressed and boneless fillet (without head and caudal fin) samples had an average length of 10.7 ± 0.8 cm, in addition, the average thickness of the sample was 1.3 ± 0.21 cm.

Fig. 1.

Fig. 1

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Cutting type and sample preparation of the Konosirus punctatus used in this study. The blue dotted line means the cutting site

The cut sample was used in the experiments after washing with tap water and draining in a polypropylene (PP) basket with holes at room temperature (25 ± 2 °C) for 10 min. V. vulnificus KCCM 41665 was purchased from the Korean Culture Center of Microorganisms (KCCM, Seoul, South Korea) and cultivated in Luria–Bertani (LB; Difco Laboratories Inc., Detroit, MI, USA) broth with 2.0% NaCl at 35 ± 2 °C for 12 h.

Effect of washing water type, temperature, and exposure time

Before developing an inactivation method against V. vulnificus contamination in K. punctatus, various factors reducing V. vulnificus were considered including the washing water type, temperature, and pH. The washing water used in the study was tap water, filtered water (BRITA, LP, Oakland, CA, USA), and phosphate buffer solution (PBS) with 2% NaCl (2% PBS, adjusted to pH 7.4). The V. vulnificus culture (1 mL) was added to three types of 9 mL washing water (tap, filtered, and 2% PBS). The initial cell population in the washing water was approximately 7 log CFU/mL, which was then exposed to four different temperatures of 0, 5, 10, and 25 °C for 1, 5, and 10 min. After treatment with washing water, 3 mL of the solution was transferred into a 50 mL conical tube and nine times the volume of PBS was added. The solution was then serially diluted to an appropriate level, spread on LB agar with 2% NaCl, and incubated at 35 °C for 12 h.

Effect of washing water pH adjusted by organic acid

After treatment with different washing water types, the most effective washing water was selected and its pH was adjusted to 3.0, 4.0, and 5.0, with three organic acids (acetic, citric, and lactic acids) to evaluate the effect of pH on the reduction of V. vulnificus. The other water conditions (temperature and exposure time) were the same as those previously described (section “Effect of washing water type, temperature, and exposure time”). All the organic acids used in this study were purchased from Sigma-Aldrich (St. Louis, MO, USA).

Preparation of fish artificially contaminated with V. vulnificus and washing method

An inoculation solution was prepared to artificially contaminate fish with V. vulnificus (ACVF). The solution was prepared by inoculating 2% PBS with pre-cultured V. vulnificus, and the final concentration of approximately 7 log CFU/mL. The samples prepared with different cutting types were placed in a stainless-steel container (110 mm × 280 mm × 210 mm) and immersed three times in the inoculated solution (W/V) for 5 or 10 min. After immersion, the samples were drained in basket as above for 10 min. All preparations for ACVF used in this study were performed immediately before the experiment.

A washing method for ACVF was investigated to identify an effective method for V. vulnificus reduction. The samples were treated using four washing methods with pH-adjusted filtered water containing organic acids (PFWO). The four washing methods were as follows: washing in PFWO for 10 s (Washing, W), washing for 10 s after immersion in PFWO for 5 min (immersion and washing, IW), scrubbing with both hands in PFWO for 10 s (20 times) (Scrubbing, S), and scrubbing for 10 s (20 times) after immersion in PFWO for 5 min (immersion and scrubbing, IS). After washing and immersion, quantitative analysis of the survival of V. vulnificus was performed as described below.

Quantitative analysis of V. vulnificus

Quantitative analysis of V. vulnificus was performed to observe the effects of organic acid treatment on ACVF. The population of V. vulnificus in the sample was analyzed using a slightly modified method of most probable number combined with polymerase chain reaction (MPN-PCR) of the Bacteriological Analytical Manual from the U.S. Food and Drug Administration (Jang et al., 2018; Jeong et al., 2021). Homogenized and serially diluted samples were inoculated into 3-tubes containing alkaline peptone water (APW; pH 8.4, Difco Laboratories, Detroit, MI, USA) and incubated at 35 °C for 12 h. After incubation, turbid tubes were selected and streaked onto thiosulfate citrate-bile salts-sucrose agar (TCBS; Difco Laboratories Inc.), and all streaked plates were incubated at 35 °C for 18–24 h. Colonies that appeared round and green on TCBS agar were selected, and PCR was performed to determine whether they were positive. The V. vulnificus cell population in the sample was determined using MPN sheets (McGough et al., 2021). The specific primers for V. vulnificus amplification were designed for the V. vulnificus vvh gene as follows (Wang & Lee, 2003); sense, 5′-CAGCCGGACGTCGTCCATTTTG-3′; antisense, 5′-ATGAGTAAGCGTCCGACGCGT-3′. The PCR conditions for the V. vulnificus vvh gene were slightly modified from those described by Panicker et al. (2004). Colony PCR was performed for 25 cycles under the following conditions: pre-denaturation at 94 °C for 5 min, denaturation at 95 °C for 30 s, annealing at 60 °C for 30 s, extension at 72 °C for 30 s, and final extension at 72 °C for 10 min.

Texture profile analysis

A CT3 texture analyzer (Brookfield Engineering Laboratories, Middleboro, MA, USA) was used to evaluate the textural characteristics of the samples after PFWO and washing treatments. The sample conditions used in the analysis of the texture profile were as follows: pan-dressed, filtered water (pH adjusted to 3.0, and 4.0 by acetic acid), and washing methods of washing (W) and immersion after washing (IW). Texture profile analysis (TPA) parameters were hardness, cohesiveness, springiness, gumminess, and chewiness. To measure texture profile, a TA11/1000 cylindrical probe (25.4 mm diameter × 35 mm length) was used, and parameters were set as a target value of 2.0 mm, trigger load of 6.8 g, test speed of 0.5 mm/s, and return speed of 0.5 mm/s. Texture profile data recording and calculations were performed using Texture Pro CT V 1.8 Build 31 software (Brookfield Engineering Labs. Inc., Stoughton, MA, USA). All measurements were repeated five times.

Sensory evaluation

Sensory evaluation of the samples treated with PFWO and washing methods was performed according to the method reported by Kim et al. (2010) with slight modifications. The sensory evaluation was conducted by 12 panelists (four males and eight females) between the ages of 22 and 30 years. The samples for sensory evaluation were treated by PFWO pH 3.0 and 4.0, and the washing (W) and immersion after washing (IW) methods were used for washing. The samples were provided to the 12 panelists in transparent plastic containers. These 12 panelists performed a 5-point scale sensory evaluation of the appearance, texture, fishy odor, sour odor, and color of the sample (5, very good; 4, good; 3, average; 2, bad; 1, very bad). This study was conducted after the approval of Pukyong National University’s Institutional Review Board [IRB no. 1041386-202306-HR-53-02].

Statistical analysis

All experiments were conducted in triplicate. Analysis of variance (ANOVA) and Duncan’s multiple range tests were conducted with SPSS (ver. 23.0, SPSS Inc., USA) to express the statistical significance of the data. A significance level of 5% (P < 0.05) was considered to indicated statistically significant differences.

Results and discussion

Changes in the survival rate of V. vulnificus depending on water washing conditions

The changes in the survival rate of V. vulnificus depending on the washing water conditions (type, temperature, and exposure time) are shown in Table 1. The viable cell counts of V. vulnificus in the untreated control group (without treatment) was 6.78 log CFU/mL. The survival cell counts of V. vulnificus treated with 2% PBS ranged from 6.87 to 6.26 log CFU/mL. The increase and decrease in the survival rate of V. vulnificus compared to the control group were − 0.52 to + 0.09 log CFU/mL. The survival rate of V. vulnificus in the samples treated with 2% PBS at different temperatures (0 °C, 5 °C, 10 °C, and 25 °C) showed statistically significant differences regardless of exposure time. The survival cell counts of V. vulnificus treated with tap water ranged from 6.71 to 6.09 log CFU/mL. The increase and decrease in the survival rate of V. vulnificus compared with the control group were − 0.69 to − 0.07 log CFU/mL. Furthermore, the levels of V. vulnificus in the sample treated with tap water were more reduced than those in the sample treated with 2% PBS due to the bactericidal effect of Cl ions in the tap water (0.2 mg per kg). Regarding the tap water results, V. vulnificus showed the lowest survival cell counts following treatment at 5 °C for 1 and 5 min. The survival cell counts of V. vulnificus in the sample treated with filtered water ranged from 6.05 to 4.75 log CFU/mL. Treatment with filtered water of various temperatures and exposure times effectively reduced V. vulnificus from 0.82 to 2.03 log CFU/mL. The highest reduction rate of V. vulnificus in the samples treated with filtered water was observed following incubation at 5 °C for 10 min; other water types, such as 2% PBS and tap water, showed a similar tendency. As a result, the temperature of 5 °C and exposure time of 5 min or longer were the most effective in reducing V. vulnificus, and filtered water showed the highest bactericidal effect among the water types. All temperatures, except 5 °C, were not effective in reducing V. vulnificus. However, treatment with filtered water effectively reduced V. vulnificus at all temperatures. These results suggest that the type of water had an effect on bactericidal activity rather than the temperature. V. vulnificus is a well-known halophilic bacterium whose survival rate depends on salt concentration. In addition, various studies have reported that exposure or storage of Vibrio spp. at a low temperature (< 10 °C) decreased survival rate, resulting in a bactericidal effect (Campbell et al., 2022; Telli and Doğruer, 2019). Additionally, Sheikh et al. (2022) reported that the optimum temperature for the survival of V. vulnificus depends on salinity, and survival sensitivity increases with decreasing temperature and low salinity.

Table 1.

Survival cell counts of Vibrio vulnificus (log CFU/mL) at different types of water, temperature, and exposure time

Temp. (°C) PBS (containing 2% of NaCl) Tap water Filtered water
Exposure time (min) Exposure time (min) Exposure time (min)
1a 5 10 1 5 10 1 5 10
0 6.44 ± 0.03CD* 6.39 ± 0.12CD 6.46 ± 0.00BCD 6.24 ± 0.26AB 6.40 ± 0.18AB 6.64 ± 0.22AB 6.05 ± 0.11A 5.66 ± 0.53A 5.69 ± 0.35A
5 6.68 ± 0.05ABC 6.87 ± 0.17A 6.82 ± 0.45A 6.09 ± 0.14B 6.10 ± 0.04B 6.15 ± 0.18AB 5.19 ± 0.20B 4.90 ± 0.06BC 4.75 ± 0.23C
10 6.77 ± 0.10A 6.63 ± 0.04ABC 6.74 ± 0.06AB 6.71 ± 0.66A 6.40 ± 0.11AB 6.25 ± 0.09AB 5.78 ± 0.09A 5.90 ± 0.10A 5.95 ± 0.18A
25 6.26 ± 0.12D 6.45 ± 0.05BCD 6.40 ± 0.12CD 6.44 ± 0.09AB 6.36 ± 0.22AB 6.12 ± 0.65AB 5.96 ± 0.15A 5.93 ± 0.15A 5.93 ± 0.13A
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*Values with different letters above the number mean that significantly different (P < 0.05)

aThe viable cell counts of V. vulnificus inoculated in each type of water was 6.78 log CFU/mL

The results presented in Table 1 are the viable cell counts of V. vulnificus inoculated in different types of solutions (2% PBS, tap water, and filtered water) at various temperatures (0, 5, 10, 25 °C) and time intervals (1, 5, and 10 min). V. vulnificus inoculated in PBS 2% and tap water group was observed that the bacterial cell count remained relatively stable for up to 10 min, indicating that they were not significantly affected by osmotic pressure between cell and water types. However, the filtered water group showed a statistical decrease in bacterial cell count with increasing exposure time, indicating a significant effect of osmotic pressure on V. vulnificus cells.

Bactericidal effect of organic acid

The effect of pH-adjusted filtered water (pH 3.0, 4.0, and 5.0) with organic acids (acetic, citric, and lactic acid) on the survival rate of V. vulnificus is shown in Fig. 2. PFWO with pH adjusted to 5.0 reduced survival cell counts of V. vulnificus from 0.33 to 1.52 log CFU/mL under all temperatures. Furthermore, PFWO with pH adjusted to 3.0 significantly reduced the survival of V. vulnificus to more than 6 log CFU/mL within 1 min at all temperatures, resulting in no detection of V. vulnificus in all samples. Bang and Drake (2005) reported that the surviving population of V. vulnificus was reduced by more than 6 log CFU/mL within 2 min of treatment with a solution with pH 3.5 adjusted by acetic acid. In addition, solutions with pH 3.0, 2.0 adjusted using hydrochloric acid reduced the survival cell count of V. vulnificus to approximately 5 log CFU/mL or more, and V. vulnificus has been reported to have difficulty surviving below pH 3.0 (Koo et al., 2000).

Fig. 2.

Fig. 2

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Effect of adjusted pH by organic acid (acetic, citric, and lactic acids) on Vibrio vulnificus viability in different temperature of filtered water. The viable cell counts of V. vulnificus inoculated in each solution was approximately 7 log CFU/mL. Results of the survival cell count of V. vulnificus in filtered water at 0 °C (A); 5 °C (B); 10 °C (C); 25 °C (D). *ND not detected; **Values with different letters above the bars mean that significantly different (P < 0.05)

PFWO with pH adjusted to 4.0 by acetic acid (PFWO-4.0A) showed a high bactericidal effect against V. vulnificus at all temperatures. Only ≤ 1 log CFU/mL of V. vulnificus was detected following treatment at 5 °C and 10 °C for 1 min, and was not detected at other temperatures. Interestingly, PFWO with pH adjusted to 4.0 by citric acid (PFWO-4.0C) and lactic acid (PFWO-4.0L) showed different tendencies depending on the temperature and type of organic acid. PFWO-4.0L did not significantly reduce V. vulnificus at any temperature and showed survival cell counts similar to those of PFWO-5.0L. However, PFWO-4.0C exhibited different results at all temperatures. Temperature conditions of 5 and 10 °C significantly reduced the survival of V. vulnificus. PFWO with pH adjusted to 5.0 by acetic, citric, and lactic acids did not significantly reduce V. vulnificus at all temperatures. PFWO with pH adjusted by acetic acid was the most effective in reducing V. vulnificus at various temperatures. Additionally, Bang and Drake (2005) reported that pH adjusted by acetic acid was more effective than that adjusted by citric acid in reducing Vibrio spp. The bactericidal effects of organic acids such as acetic and citric acids are related to the amount of undissociated acid (Pearlin et al., 2020). The bactericidal effect of organic acids depends on the dissociation constant (pKa), that is, more undissociated acid results in higher bactericidal efficacy, as the undissociated acid can penetrate the cell membrane and lower the internal pH of the cell (Ben Braïek and Smaoui, 2021). In addition, Rathod et al. (2021) reported that lower molecular weight organic acids such as acetic acid are more effective than higher molecular weight organic acids such as citric acid. The effect of organic acids in reducing V. vulnificus appeared in the order of acetic acid > citric acid > lactic acid. It was also observed that a lower pH of water showed a higher bactericidal effect, and the temperature also affected the bactericidal effect.

Preparation of artificially contaminated fish fillets

The sample (K. punctatus) was cut into three types, semi-dressed, pan-dressed, and boneless fillet, to evaluate the bactericidal effect of washing water depending on the cutting type. The ACVF was prepared before evaluation. As described in section “Quantitative analysis of V. vulnificus”, the survival counts of V. vulnificus in the fish samples were quantified using MPN-PCR (MPN/100 g). The artificial contamination level of Semi-dressed was determined to be 5.92 ± 0.73 log MPN/100 g for 5 min and 5.54 ± 0.39 log MPN/100 g for 10 min. For Pan-dressed, the contamination level was found to be 5.63 ± 0.30 log MPN/100 g for 5 min and 5.50 ± 0.22 log MPN/100 g for 10 min. Lastly, the boneless fillet exhibited a contamination level of 5.19 ± 0.14 log MPN/100 g for 5 min and 5.23 ± 0.50 log MPN/100 g for 10 min. Statistical analysis revealed no significant difference in the contamination level among the different samples. Kim et al. (2015) reported that sterilization methods for various fish and the levels of artificial contamination of halibut, yellowtail, and scallops by V. parahaemolyticus were approximately 7 log CFU/g. Therefore, samples artificially contaminated with V. vulnificus were used to evaluate the effect of the washing water type and method.

Bactericidal effect of organic acid treatment on artificially contaminated fish samples

Traditionally in Korea, K. punctatus is consumed raw (sashimi) including its skin, and the only cleaning process involved is rinsing its fillet with tap water and draining it. As shown in Table 1, rinsing with tap water had no significant effect on the reduction of V. vulnificus. However, rinsing with pH adjusted water using organic acid (Fig. 2) showed a significant reduction in V. vulnificus without compromising the texture characteristics of the K. punctatus. Figure 3 shows the bactericidal effect of PFWO on ACVF in combination with washing methods. Quantitative analysis of V. vulnificus in the sample was performed using MPN-PCR, and acetic acid was the most effective organic acid to reduce V. vulnificus (Fig. 2). Therefore, acetic acid was selected for use in the present study for pH adjustment. Artificial contamination of the samples with V. vulnificus was effectively reduced by washing with PFWO with pH adjusted using acetic acid. The bactericidal effect was observed in the order of pan-dressed > boneless > semi-dressed. The IW and IS methods, including immersion and washing, showed significantly higher bactericidal effects than the other methods. In particular, the pan-dressed sample showed the highest bactericidal effect, which meant that the bactericidal effect of the immersion and washing methods differed significantly depending on the cutting type. V. vulnificus in pan-dressed samples was reduced by approximately 1.00 log MPN/100 g or more when IW was performed using filtered water only. V. vulnificus in the pan-dressed sample was effectively reduced to 2.50 log MPN/100 g or more when the IW or IS was performed with PFWO with an adjusted pH of 3.0, using acetic acid (PFWO-3.0A).

Fig. 3.

Fig. 3

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Bactericidal effect of the acidic solution on semi-dressed (A), pan-dressed (B), and boneless fillet (C) of Konosirus punctatus contaminated with Vibrio vulnificus. NC negative control (only contamination, without treatment), W washing, IW immersion after washing, S scrubbing while washing, IS immersion after scrubbing while washing

The minimum and maximum reductions of V. vulnificus in the semi-dressed sample were 0.16 and 1.39 log MPN/100 g, respectively. Similar to the pan-dressed samples, a higher bactericidal effect was observed with the IW and IS methods. The highest bactericidal effects in the three cutting types of samples were observed with the IW and IS methods using PFWO-3.0A. The minimum and maximum reductions of V. vulnificus in the boneless sample were 0.20 and 2.12 log MPN/100 g, respectively. Similar to other cutting types, the highest bactericidal effect in boneless samples was observed using the IW and IS methods. In addition, IW using PFWO-3.0A showed the highest bactericidal effect in boneless samples among the three cutting types, but the bactericidal effect of the other washing methods (W, S, and IS) was observed to be lower than that of the pan-dressed sample. The synergistic effect between washing and PFWO was confirmed by comparison with the results of the control and experimental groups that used only filtered water without pH adjustment.

Various studies have reported the control and reduction of microbial levels through biological, physical, and chemical treatment of seafood, such as fish fillets, raw fish, and shellfish (Castrica et al., 2021; Houicher et al., 2021; Zhao et al., 2021) These treatments have the disadvantage of altering the basic physical, chemical, and sensory properties of a sample. However, the present study suggests a simple and effective method for reducing V. vulnificus contamination in fish without deteriorating the basic properties and quality of fish, and the method suggested in this study should not affect texture and sensory profiles.

Changes in texture profile of sample after organic acid treatment

Table 2 shows the texture profile analysis (TPA) of the samples after washing with PFWO. TPA was performed with the pan-dressed sample, which showed the highest bactericidal effect among the three cutting types (Fig. 3). There were no statistically significant differences between most samples and controls. Only IW-3.0, which was treated with a washing process after immersion for 5 min in PFWO with an acetic acid-adjusted pH of 3.0, showed a statistically significant difference. Washing with pH-adjusted PFWO decreased the hardness, springiness, gumminess, and chewiness of the sample. The hardness of the W-4.0 and IW-4.0 was decreased from 282.67 and 283.50 to 235.83 and 238.17 compared with non-treatment (NT) and W, respectively. However, there was no significant difference in other TPA parameters, such as cohesiveness, springiness, gumminess, and chewiness. The low pH of the solution is able to induce acidolysis related with texture profile and sensory properties of fish meat (Gu et al., 2021; Klinmalai et al., 2021). Jo et al. (2021) reported that ribbon fish fillets treated with citric acid solution showed a reduction in the texture profile, similar to our results. In addition, the cohesiveness, springiness, gumminess, and chewiness of all samples except for IW-3.0 were not statistically significantly different compared with NT and W. IW-3.0 showed a lower TPA than the other treatment conditions except for cohesiveness, which meant that IW-3.0 was able to change the texture and deteriorate the quality of the sample. Consequently, TPA results showed that the PFWO washing method (W and IW) could affect the texture of the sample, but W-4.0 and IW-4.0 were not significantly different from the control (NT and W).

Table 2.

Texture profile of samples treated by filtered water with adjusted pH by acetic acid

Treatment condition Hardness (g) Cohesiveness Springiness (mm) Gumminess (g) Chewiness (mJ)
NT 282.67 ± 36.69a* 0.62 ± 0.03a 1.68 ± 0.02a 160.47 ± 8.00a 2.56 ± 0.10a
W 283.50 ± 73.26a 0.65 ± 0.02a 1.61 ± 0.01a 161.95 ± 32.95a 2.93 ± 0.82a
W-4.0 235.83 ± 39.03ab 0.68 ± 0.04a 1.67 ± 0.12a 160.87 ± 31.24a 2.63 ± 0.67a
IW-4.0 238.17 ± 52.39ab 0.66 ± 0.07a 1.61 ± 0.07a 151.33 ± 24.64a 2.39 ± 0.48ab
W-3.0 201.50 ± 40.07ab 0.65 ± 0.05a 1.62 ± 0.09a 165.37 ± 22.43a 2.66 ± 0.51a
IW-3.0 173.00 ± 12.82b 0.60 ± 0.02a 1.44 ± 0.03b 104.97 ± 11.59b 1.57 ± 0.23b
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NT non-treatment, W washing with filtered water W-4.0 washing with filtered water with adjusted pH to 4.0 by acetic acid, IW-4.0 immersion after washing with filtered water with adjusted pH to 4.0 by acetic acid, W-3.0 washing with filtered water with adjusted pH to 3.0 by acetic acid, IW-3.0 immersion after washing with filtered water with adjusted pH to 3.0 by acetic acid

*Means with different superscripts within each column indicate significant differences by Duncan’s multiple range test (P < 0.05)

Sensory evaluation of samples treated with organic acid

The results of the sensory evaluation of semi-dressed samples treated with PFWO are shown in Fig. 4. The combination of PFWO and the wash method showed no significant effects on appearance and color, and the appearance value of all samples was 4.0 or higher. NT and IW-3.0 showed the highest and lowest fishy odor value scores, respectively. W, W-4.0, and IW-4.0, showed fishy odor values of approximately 3.0, which were evaluated at very similar levels. In addition, the sour odor value of all samples was evaluated to be below 3.0, and there was no significant difference between the samples. The texture value had a tendency similar to the TPA results, and W-4.0 and IW-4.0 showed high scores. These results indicate that PFWO with an adjusted pH of 4.0 had no effect on the texture of the sample. The fishy odor values showed the highest and lowest scores in NT and IW-3.0, respectively. Trimethylamine (TMA) is a well-known major compound of fishy odor, and it smells a pungent odor according to pH variation (Kim et al., 2017). In addition, TMA exists in large amounts in the muscle of marine-derived organisms, such as fish and shells, and is produced during the decomposition process by microorganisms or self-degradation (Sun et al., 2019). According to Kim et al. (2017), acetic acid treatment can decrease the TMA content by acting as a proton donor to covert TMA in a non-volatile salt. In addition, Park et al. (2020) reported that lactic acid bacteria cultured in an acidic pH medium showed a decrease in TMA to 92.14%. Therefore, the treated sample scored a lower fishy odor than the NT sample because acetic acid reacted with TMA in the samples. Ko et al. (2016) reported the effects of various raw fish odors and textures on consumer preferences. Similarly, the results of this study showed that the texture and odor of fish have a significant influence on consumer preference. PFWO-3.0 treatment resulted in higher scores for sour odor than PFWO-4.0 (W and IW) and lower scores for texture and fishy odor than PFWO-4.0 (W and IW) and control (NT and W). However, PFWO-4.0 (W-4.0 and IW-4.0) showed a lower score for the fishy odor than that of the NT, and there was no significant difference from the NT regarding other odors. Interestingly, the texture values for W-4.0 and IW-4.0 showed higher scores than those of NT. Briefly, W-4.0 and IW-4.0 effectively reduced V. vulnificus without deteriorating the sensory quality of the sample.

Fig. 4.

Fig. 4

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The sensory evaluation results on the acidic solution treatment for pan-dressed Konosirus punctatus. NT non-treatment, W washing with filtered water, W-4.0 washing with filtered water with adjusted pH to 4.0 by acetic acid, IW-4.0 immersion after washing with filtered water with adjusted pH to 4.0 by acetic acid, W-3.0 washing with filtered water with adjusted pH to 3.0 by acetic acid, IW-3.0 immersion after washing with filtered water with adjusted pH to 3.0 by acetic acid

This study aimed to evaluate a method for effectively reducing V. vulnificus contamination in fish samples using a wash method combined with PFWO whose pH was adjusted using an organic acid. Various factors, including water type, temperature, exposure time, type of organic acids, pH, and washing method, which have the potential to affect the survival rate of V. vulnificus, were reviewed. TPA and sensory evaluation were performed to determine the effect of the developed method on the quality and consumer preference of the samples. Consequentially, PFWO-4.0 (W and IW) showed high bactericidal efficacy against V. vulnificus contamination in the sample, as well as excellent TPA and sensory evaluation scores compared with NT. If the washing method of raw fish is improved by PFWO-4.0 (W and IW), it can effectively reduce V. vulnificus infection in raw fish. Additionally, this method, which involves washing with PFWO, does not deteriorate texture and sensory characteristics; therefore, the preference of the customer can be maintained for raw fish. Finally, the washing method with PFWO-4.0 (W and IW) is a simple, effective, and field-applicable method for preventing V. vulnificus infection of raw fish.

Acknowledgements

This research was supported by the Korea Institute of Marine Science & Technology Promotion (KIMST) and funded by the Ministry of Oceans and Fisheries (20210695 and 20200377). We would like to thank Editage (www.editage.co.kr) for English language editing.

Declarations

Conflict of interest

All authors declare that they have no conflict of interest.

Footnotes

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Seul-Ki Park and Daeun Lee both authors are contributed equally to this work.

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