Synergistic Effects of NaOCl and Ultrasound Combination on the Reduction of E s cherichia coli and Bacillus cereus in Raw Laver

Abstract

The current study investigated the synergistic effects of NaOCl (50–200 ppm)/ultrasound (37 kHz, 380 W for 5–100 min) combination on the reduction of Escherichia coli and Bacillus cereus in raw laver. The synergistic reductions were not dependent on concentrations of NaOCl and times of ultrasound. Synergistic reduction ranged from 0.1 to 0.5 log₁₀ colony-forming units (CFU)/g and 0.1–1.1 log₁₀ CFU/g, respectively, for E. coli and B. cereus, with the largest synergistic reduction in the combination of 200 ppm NaOCl and 60-min ultrasound. Moreover, significant differences of “L” (lightness), “a” (redness), and “b” (yellowness) were not observed in combined with 50–200 ppm NaOCl and 100-min ultrasound compared to those in raw laver treated by only 100-min ultrasound. The results in the current study indicate that the combined treatment of 200 ppm NaOCl and 60-min ultrasound could be regarded a potential optimum hurdle approach in the seaweed production, processing, and distribution process to enhance seaweed safety.

Introduction

Raw laver (Porphyra tenera ) is classified as one of the seaweed vegetables and commonly processed into many commercial seaweed products including dried seasoned laver and roasted laver for sushi. The dried seasoned laver and roasted laver are widely consumed in Korea, Japan, and China because they are high in protein, minerals, vitamins, and other nutrients with a pleasing taste to people in those three countries. Moreover, there is an increasing utilization of raw laver as a material for diet foods and cosmetics in Korea.

However, the microbial contamination in raw laver was the highest among unprocessed seaweed products (Kim et al., 2006; Cho et al., 2009; Wang et al., 2011). The total aerobic bacteria counts and coliform counts were 2.8–7.1 and 1.0–1.8 log₁₀ colony-forming units (CFU)/g, respectively, in Korean dried laver (Kim et al., 2006). A total of 3% (<1 log₁₀ CFU/g) and 12% (<1 log₁₀ CFU/g) of dried laver samples in Korea were contaminated by Clostridium perfringens and Bacillus cereus, respectively (Kim et al., 2006). B. cereus was also detected in 8% (<1 log₁₀ CFU/g) of kelp samples and 18.5% (1 log₁₀ CFU/g) of brown seaweed samples in Korea (Kim et al., 2006). C. perfringens and Vibrio parahaemolyticus were not detected in other seaweeds in Korea (Kim et al., 2006). Thus, B. cereus may be a main seafood pathogen of significant public concern.

There are many disinfectants that are classified into chemical or physical sanitizers that have been used in the food industry in the last decade. The common chemical sanitizers are chlorine, hydrogen peroxide, ethanol, and ozone (Beuchat, 1997; Mermelstein, 1998; Piernas and Guiraud, 1998, Wisniewsky et al., 2000; Chang et al., 2004), while the common physical sanitizers are heating (Browne and Dowds, 2001), high-voltage pulsed electric fields (Terebiznik et al., 2000; Gachovska et al., 2008), high hydrostatic pressure (Cléry-Barraud et al., 2004), ultrasound (Demirdőven and Baysal, 2009; Zhou et al., 2009), ultraviolet radiation (Ukuku and Geveke, 2010; Ha et al., 2012), and electron beam irradiation (Sarrias et al., 2003). Among these technologies, ultrasound has been identified as a potential physical technique of causing antimicrobial effects (Piyasena et al., 2003; Baumann et al., 2005; Arroyo et al., 2011). Ultrasound is a longitudinal wave having a frequency above 20 kHz (Leighton, 1994), and the frequency used in the food industry ranges from 20 kHz to 10 MHz (Piyasena et al., 2003). Ultrasound can potentially be used for the treatment of contaminated fresh produce, but this has not been adopted because of the perceived adverse effect on food quality. This is brought about by high-intensity treatments required to inactivate the most resistant microorganisms.

The mechanism of ultrasound is based on the production of powerful cavitation bubbles, which can disrupt the lipid membrane of bacteria and detach bacteria attached to the surfaces of foods (Hughes and Nyborg, 1962; Ordoñez et al., 1987; García et al., 1989; Scouten and Beuchat, 2002; Seymour et al., 2002; Piyasena et al., 2003). Hughes and Nyborg (1962) originally found that micromechanical shocks can be created by making and breaking microscopic bubbles induced by fluctuating pressures under the ultrasound process. The shocks can disrupt cellular structural and functional components up to cell lysis. Sodium hypochlorite (NaOCl) is a chlorine compound commonly used as a disinfectant in the food industry because it is easy to handle, inexpensive, and effective in reduction of microorganisms (Dychdala, 2001; Peng et al., 2002). The bacteriocidal efficacy of NaOCl is based on the penetration of the chemical and its oxidative action on essential enzymes in the bacterial cell (Kumar and Anand, 1998; Lomander et al., 2004). NaOCl can become HOCl (unionized form) through hydrolysis (NaOCl+H₂O→HOCl+NaOH^-), which is a strong bactericidal agent. Hypochlorous acid (HOCl) is a weak acid and dissociates to the hypochlorite ion (^-OCl) and proton (H⁺), depending on the solution pH (Fukuzaki, 2006).

Various combinations of chemical and physical disinfectants have been studied to reduce pathogenic bacteria populations, simultaneously, with no quality loss (Chawla et al., 2006; Kanatt et al., 2006). Lillard (1993) observed that the combined treatment of chlorine (0.5 ppm) and 20-kHz ultrasound gave a 2.4–4-log reduction of Salmonella spp. on chicken skin. In addition, Seymour et al. (2002) reported that Salmonella Typhimurium was further reduced by 1 log unit on iceberg lettuce by cleaning with combined treatment of chlorine (25 ppm) and ultrasound (32–40 kHz, 10–15 W/L) for 10 min as compared with ultrasound or chlorine alone. Scouten and Beuchat (2002) found that ultrasound (38.5–40.5 kHz) in combination with 1% Ca (OH)₂ enhanced the decontamination efficacy against S. enterica and E. coli O157:H7 on alfalfa seeds. Huang et al. (2006) reported that additional reductions up to 1 log unit were found for S. enterica and E. coli O157:H7 on apples in combination with ultrasound (170 kHz) and ClO₂ (20 and 40 ppm), but no increase in log reduction was found for E. coli O157:H7 on lettuce. Ajlouni et al. (2006) reported that the effects of ultrasonication (40 kHz) on the inactivation of natural microflora on Cos lettuce was not observed in a sanitizer (0.02% peracetic acid, 4 mg/L hydrogen peroxide, 2% acetic acid, 100 mg/L chlorinated water) wash for 20 min except with 200 mg/L chlorinated water. Sagong et al. (2013) reported that 2.49 and 2.22 log reduction of B. cereus spores on lettuce and carrots, respectively, were achieved by the combination of ultrasound (40 kHz) and surfactant (0.1% Tween 20). In our previous study, B. cereus spores in raw rice were reduced by 1.35 log after a combination treatment of NaOCl (1000 ppm chlorine) and ultrasound (37 kHz) for 20 min without causing deterioration of quality (Ha et al., 2012).

There is a need to further examine any synergistic effects of combined treatment of chlorine and ultrasound on food decontamination, especially during washing. The present study was therefore undertaken to determine the synergistic effects of NaOCl (50–200 ppm) and ultrasound (37 kHz, 380 W for 5–100 min) combination on the reductions of E. coli and B. cereus in raw laver.

Materials and Methods

Bacterial strains

The strains used were E. coli ATCC 10536 and B. cereus F4810/72. A stock culture (10⁸ CFU/mL) was maintained at −70°C in tryptic soy broth (TSB, Difco Laboratories, Detroit, MI) containing 30% glycerol. To obtain a working culture, each strain was cultured twice at 37°C for 18 to 24 h in TSB, streaked onto a tryptic soy agar (TSA; Difco, Becton Dickinson) plate, incubated at 37°C for 18 to 24 h, examined for typical and homogeneous colony morphology, and then used immediately at room temperature.

Inoculation of raw laver

Cell populations of E. coli ATCC 10536 or B. cereus F4810/72 used for the inoculum were 7–8 log₁₀ CFU/mL. All B. cereus F4810/72 were vegetative cells. Inoculum of the strain was prepared in TSB by incubation at 35°C for 24 h. Cell suspensions of the strain were centrifuged at 10,000×g for 10 min and suspended in 10 mL of buffered peptone water (PW), and bacterial cell counts were determined by plating on TSA and incubating for 24 h at 35°C. Raw laver (Porphyra tenera) was obtained from a food processing plant (Puan, Korea) and stored at 4°C a day before the experiment. Water present in raw laver was removed by gentle squeezing with hands. Three of raw laver in a sterilized petri dish were dried for 20–30 min in a laminar floor hood (Vision Scientific Co., Seoul, Korea) with fan running. The sample (3 g) was dipped for 10 min in 9 mL of buffered peptone water (PW) containing cell suspension (7–8 log₁₀ CFU/mL). The inoculated sample in a sterilized petri dish was dried for 2 h in a laminar floor hood (Vision Scientific Co., Seoul, Korea) with fan running and was used immediately for further experiments.

Single and combined treatment of NaOCl and ultrasound

For the NaOCl single treatment, 12% NaOCl (Shimadzu Co., Kyoto, Japan) was diluted with tap water to get 50 mL of 50, 100, 150, and 200 ppm. The inoculated samples (3 g) were immersed in each NaOCl treatment at room temperature for 5 min with mild agitation. The sanitizers were all diluted with tap water to their respective target concentrations. For ultrasound treatments, inoculated samples (3 g) were immersed in 50 mL of sterile distilled water and treated in an ultrasound tank for 5, 20, 40, 60, 80, or 100 min at intensities of 0.071 W/cm³ (37 kHz, 380 W P300H, Elma GmbH, Germany). For combined treatments, the four NaOCl treatments were first conducted as a primary disinfectant, and the six ultrasound treatments followed immediately as a secondary disinfectant as described by Koivunen and Heinonen-Tanski (2005).

Synergistic reduction effects

To estimate any synergistic effect on bacterial inactivation, the inactivation values of NaOCl and ultrasound combination were compared with those of NaOCl or ultrasound alone. The procedure described by Koivunen and Heinonen-Tanski (2005) was used for the combined disinfectant treatments. The combined disinfection experiments were carried out by first applying NaOCl as the primary disinfectant and then ultrasound as the secondary disinfectant. Ultrasound was used after the NaOCl disinfectants to take advantage of the possible increased intracellular cavitation bubbles due to the acceleration of diffusion, which may result in increased synergistic effects. The efficacy of disinfection after the different treatments was determined by measuring microbial reduction. The synergistic reduction effect values of combined NaOCl and ultrasound were calculated using the following equation: \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*} {\rm Value \ of \ synergistic \ reduction} = {\rm A - (B+ C)} \end{align*} \end{document}

Where A was the reduction from combined NaOCl and ultrasound disinfection, B was the reduction from NaOCl disinfection alone, and C was the reduction from ultrasound disinfection alone. On the basis of this equation, a synergistic and antagonistic reduction effect was indicated as plus values and minus values, respectively.

Microbiological counts

The treated sample (3 g) was homogenized for 2 min in a sterile 24 oz (710 mL) Whirl-Pak^® filter bag (Nasco, Fort Atkinson, WI) containing 27 mL of sterile 0.1% PW using a stomacher (Bag mixer^® 400; Interscience Co., France). A liquid aliquot sample was taken from the homogenate sample, diluted with 0.1% PW, and plated in duplicate on appropriate growth media. Media for enumeration of E. coli and B. cereus were prepared using a 3M Petrifilm^™ E. coli (3M Microbiology Products, St. Paul, MN) and mannitol egg yolk polymyxin agar (MYP, Difco Laboratories, Detroit, MI), respectively, and the plates were incubated at 37°C for 48 h. Colonies presenting a pink or purple color with an irregular edge surrounded by a white area were considered positives for B. cereus and were enumerated. The CFU per gram were counted at a dilution of 30–300 CFU per plate. Triplicate samples from each single and combined treatment were analyzed for microbial counts.

Color measurement and statistical analysis

The treated sample (3 g) was placed into a petri dish (20×12 mm), and the color of the treated sample (3 g) was measured using a color-difference meter (UltraScan Pro/Hunterlab, USA). Color was expressed as “L” (lightness), “a” (redness +, greenness −), and “b” (yellowness +, blueness −) (Hunter and Harold, 1987). The standard plate was 97.47 as “L,” −0.22 as “a,” and 0.01 as “b.” Color data were analyzed using the analysis of variance procedure of SAS (Version 8.1, SAS Institute Inc., Cary, NC). The significant (p<0.05) means were separated using Duncan's multiple-range test.

Results

Synergistic reductions of NaOCl and ultrasound on E. coli counts in raw laver

To determine bacteriocidal effects of NaOCl and ultrasound against E. coli in raw laver, the reductions of E. coli under different NaOCl concentrations and treatment times with ultrasound are shown in Table 1. After treatment with 50, 100, 150, and 200 ppm NaOCl alone, the E. coli counts were reduced by 0.4, 0.6, 1.0, and 1.2 log₁₀ CFU/g, respectively. The E. coli counts were reduced by 0.6, 0.9, 0.9, 0.8, 0.9, and 1.1 log₁₀ CFU/g after treatment with 5, 20, 40, 60, 80, and 100 min of ultrasound alone, respectively. The maximum reduction of E. coli was by 2.7 log₁₀ CFU/g after treatment with a combination of 200 ppm NaOCl and 100-min ultrasound. Table 2 shows the synergistic effects of NaOCl/ultrasound combination on the reduction of E. coli in raw laver. Unexpectedly, antagonistic reduction effects against E. coli were observed in combination with 50 ppm NaOCl/60-min ultrasound, 50 ppm NaOCl/80-min ultrasound, 50 ppm NaOCl/100-min ultrasound, 100 ppm NaOCl/20-min ultrasound, 100 ppm NaOCl/80-min ultrasound, 150 ppm NaOCl/20-min ultrasound, 150 ppm NaOCl/60-min ultrasound, and 150 ppm NaOCl/80-min ultrasound. However, synergistic reduction effects against E. coli were observed for many other combined treatments. Specifically, synergistic reduction effects against E. coli were observed when 200 ppm NaOCl was combined with ultrasound at any treatment times. The mean synergistic reduction value for treatments of raw laver was 0.3 log₁₀ CFU/g after a combined treatment of 200 ppm NaOCl with any ultrasound exposure times. The largest synergistic reduction value for treatments of E. coli in raw laver was 0.5 log₁₀ CFU/g after the combination with 200 ppm NaOCl and 60-min ultrasound. The most synergistic reduction value for treatment of laver was <0.5 log₁₀ CFU/g. Moreover, the synergistic reduction effects against E. coli were not dependent on concentrations of chlorine or treatment times with ultrasound.

Table 1.

Reduction of Escherichia coli and Bacillus cereus in Raw Laver After the Treatment of Ultrasound and NaOCl Alone and NaOCl/Ultrasound Mixture

	Mean (±SD) reduction value (log₁₀ CFU/g)
	NaOCl (ppm)
Target organism	Ultrasound (min)	0	50	100	150	200
E. coli	0	—	0.4±0.1	0.6±0.0	1.0±0.2	1.2±0.3
	5	0.6±0.1	1.1±0.1	1.3±0.2	1.9±0.0	2.0±0.1
	20	0.9±0.4	1.7±0.0	1.4±0.3	1.7±0.4	1.9±0.2
	40	0.9±0.4	1.4±0.4	1.5±0.5	2.2±0.4	2.5±0.4
	60	0.8±0.1	0.9±0.3	1.6±0.7	1.6±0.5	2.6±0.3
	80	0.9±0.2	1.0±0.1	1.1±0.2	1.9±0.0	2.4±0.5
	100	1.1±0.0	1.3±0.2	1.9±0.4	2.2±0.6	2.7±0.5
B. cereus	0	—	0.7±0.2	1.0±0.5	1.2±0.4	1.8±0.1
	5	0.1±0.0	1.1±0.1	1.2±0.1	1.4±0.3	2.6±0.2
	20	0.4±0.0	1.1±0.1	1.5±0.1	1.6±0.5	2.7±0.2
	40	0.4±0.1	1.1±0.1	1.8±0.2	1.9±0.9	2.6±0.1
	60	0.4±0.2	1.2±0.1	1.9±0.6	2.1±1.9	3.2±1.9
	80	0.6±0.5	1.6±0.6	2.1±0.1	2.2±0.7	3.3±1.3
	100	0.6±0.3	1.2±0.6	1.8±0.0	2.6±0.2	3.0±0.4

SD, standard deviation; CFU, colony-forming units.

Table 2.

Synergistic and Antagonistic Effects of NaOCl/Ultrasound Mixture on the Reduction of Escherichia coli and Bacillus cereus

	Mean (±SD) synergistic ^a and antagonistic ^b value of reduction (log₁₀ CFU/g)
	NaOCl (ppm)
Target organism	Ultrasound (min)	50	100	150	200
E. coli	5	0.1±0.3	0.2±0.1	0.4±0.3	0.3±0.2
	20	0.4±0.5	−0.0±0.6	−0.2±1.0	0.2±0.3
	40	0.1±0.0	0.0±0.2	0.3±0.2	0.4±0.3
	60	−0.4±0.3	0.2±0.6	−0.2±0.6	0.5±0.0
	80	−0.3±0.2	−0.3±0.0	−0.1±0.4	0.3±0.4
	100	−0.2±0.3	0.3±0.3	0.0±0.8	0.4±0.2
B. cereus	5	−0.2±0.4	−0.4±0.6	−0.5±0.2	0.7±0.1
	20	0.0±0.2	0.1±0.4	−0.0±0.1	0.5±0.3
	40	−0.0±0.0	0.3±0.1	0.2±0.8	0.3±0.1
	60	0.2±0.6	0.5±0.4	0.6±0.9	1.1±2.0
	80	0.3±0.2	0.5±1.2	0.4±0.2	0.8±1.9
	100	−0.0±0.3	0.3±1.3	0.9±1.3	0.7±1.2

Synergistic effects indicated as+= (reduction achieved with the NaOCl treatment and the ultrasound treatment)−(reduction achieved by the NaOCl+ultrasound treatment).

Antagonistic effects indicated as –=(reduction achieved with the NaOCl treatment and the ultrasound treatment)−(reduction achieved by the NaOCl+ultrasound treatment).

Synergistic reductions of NaOCl and ultrasound on B. cereus counts in raw laver

The bacteriocidal effects of NaOCl and ultrasound on B. cereus in raw laver were determined after treatments with four NaOCl concentrations and six ultrasound exposure times as used previously for the reduction of E. coli (Table 1). After treatment with 50, 100, 150, and 200 ppm NaOCl alone, the B. cereus counts were reduced by 0.7, 1.0, 1.2, and 1.8 log₁₀ CFU/g, respectively. Reductions after treatment with 5, 20, 40, 60, 80, and 100 min of ultrasound alone were 0.1, 0.4, 0.4, 0.4, 0.6, and 0.6 log₁₀ CFU/g, respectively. These findings may indicate that reductions in the B. cereus counts were primarily dependent on the NaOCl concentration rather than the treatment time with ultrasound. The maximum reduction of B. cereus was 3.3 log₁₀ CFU/g after combination of 200 ppm NaOCl and 80 min of ultrasound. Table 2 shows the synergistic effects of NaOCl/ultrasound combination on the reduction of B. cereus in laver. Unexpectedly, antagonistic reduction effects against B. cereus were observed in combined treatment with 50 ppm NaOCl/5-min ultrasound, 50 ppm NaOCl/40-min ultrasound, 50 ppm NaOCl/100-min ultrasound, 100 ppm NaOCl/5-min ultrasound, 150 ppm NaOCl/5-min ultrasound, and 150 ppm NaOCl/20-min ultrasound. However, synergistic reduction effects against B. cereus were observed in many other combined treatments, especially when 200 ppm NaOCl was applied regardless of ultrasound exposure time, which was similarly observed in E. coli. The mean synergistic reduction value for treatments of raw laver was 0.7 log₁₀ CFU/g after a combined treatment of 200 ppm NaOCl and any treatment times with ultrasound. The largest synergistic value for treatments of raw laver was 1.1 log₁₀ CFU/g (>90%) with combined 200 ppm NaOCl and 60-min ultrasound. Moreover, the synergistic reduction effects against B. cereus were not dependent on concentrations of chlorine and treatment times with ultrasound. The value of zero indicated that the efficiency of combined 50 ppm NaOCl and 20-min ultrasound (0.0 of synergistic reduction values) was the same as the sum of the two individual treatments. The combination treatment of 200 ppm NaOCl and 60-min ultrasound was as an ideal choice for reducing the populations of both E. coli and B. cereus in raw laver.

Color analysis on raw laver treated by NaOCl and ultrasound

To determine a visual difference between single and combined treatments, “L” (lightness), “a” (redness), and “b” (yellowness) values were measured on the surface of raw laver (Table 3). No significant differences (p>0.05) of “L,” “a,” and “b” were observed between samples of 100-min ultrasound and 100-min ultrasound/NaOCl combination regardless of concentration. Moreover, the differences in overall acceptance for sensory qualities were not observed between the laver treated in combination of 50–200 ppm NaOCl and 100-min ultrasound and the laver treated in a single treatment with 100-min ultrasound (data not shown). Based on this, it was concluded that the raw laver may not have any color and sensory changes after a combination treatment of 200 ppm NaOCl and 60-min ultrasound as an optimal treatment for reducing E. coli and B. cereus.

Table 3.

Comparison of Color Changes (L, a, b) on Raw Laver After Treatment with Ultrasound/NaOCl Mixture

	100 min of ultrasound (35 kHz, 380 W)
	NaOCl (ppm)
Color	0	50	100	150	200
“L”^a	26.7±1.1	26.9±1.1	30.0±1.5	26.5±0.5	26.9±1.1
“a”^b	2.3±0.1	2.4±0.3	2.3±0.2	2.6±0.2	2.6±0.1
“b”^c	0.9±0.1	1.0±0.1	1.1±0.1	0.9±0.2	1.0±0.1

“L” values=lightness (0=dark, 100=bright).

“a” values=redness/greenness (+= red, −=green).

“b” values=yellowness/blueness (+=yellow, −=blue).

Discussion

Currently, the consumption of seaweed has been continuously increasing, and the utilization of raw seaweed materials was extended to kelp (Laminaria japonica), sea mustard (Undaria pinnatifida), and laver (Porphyra tenera) in Korea. These sea vegetables are further utilized to manufacture functional foods, natural seasonings, diet food, and for cosmetic purposes. Among the seaweeds, seasoned and dry-roasted laver is one of the common side dishes in a regular meal enjoyed by people of most ages in Korea (Bae, 1991; Lee, 2010). However, there is no regulation about microbiological standards of raw laver in Korea. Kim et al. (2006) reported that the raw laver in Korea was contaminated with 5.3 log₁₀ CFU/g of total aerobic bacteria, 1.4 log₁₀ CFU/g of total coliforms, and <1.0 log₁₀ CFU/g of B. cereus. According to Solberg et al. (1990), the recommended standards for the total aerobic bacteria and coliforms of nonthermal processed foods were <5 and <3 log₁₀ CFU/g, respectively. The level of 5.3 log₁₀ CFU/g of total aerobic bacteria was not satisfied with the recommended standards by Solberg et al. (1990). Even though the total coliform levels were satisfied with the recommendations given by Solberg et al. (1990), the 1.4 log₁₀ CFU/g of coliforms may include enteropathogenic E. coli, which is considered one of the most dangerous foodborne bacterial pathogens (Ray, 2004).

Kelp and sea mustard were also contaminated with <10 and 10 CFU/g of B. cereus, respectively. E. coli is typically regarded as an indicator organism for fecal contamination in all environments and foods. B. cereus is a potential emerging seaweed pathogen associated with public significance. Therefore, these two organisms are considered the main target organisms in raw laver and other seaweeds for the control of hygiene and foodborne illness. Furthermore, the regulation of microbial standards and specification need to be established, including total aerobic bacteria, E. coli, and B. cereus of raw laver for aspects of food safety and food quality in Korea.

The results in the current study provide additional evidence that combined NaOCl–ultrasound disinfection treatments resulted in synergistic benefits for reducing E. coli and B. cereus in raw laver. Ultrasound (37 kHz) alone was not greatly effective for reducing both E. coli and B. cereus counts alone, but including it did enable us to reduce the NaOCl concentration added. Our findings suggest that the combination of 200 ppm NaOCl and 60-min ultrasound could serve as a potential optimum hurdle in seaweed production, processing, and distribution to enhance seaweed safety without any changes in the food qualities.

Footnotes

Acknowledgments

This research was supported by a grant (12162KFDA) from Korea Food and Drug Administration in 2012 for studies on hazard microbiological safety management of seafood.

Disclosure Statement

No competing financial interests exist.

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