KR100770692B1 - Method for shelf-life extension of oyster by high hydrostatic pressure treatment - Google Patents

Abstract

A method of increasing oyster shelf-life by ultra high pressure treatment is provided to increase the shelf-life of the oyster maximally while maintaining the quality by sterilizing Vibrio parahaemolyticus and Escherichia coli in pathogenic microorganisms or putrefactive microorganisms. A live oyster containing Vibrio parahaemolyticus and Escherichia coli is subjected to ultra high pressure treatment at 0 to 22deg.C and 100 to 400MPa for 5 to 45min, preferably at 22deg.C and 350MPa for 15min or 10deg.C and 350MPa for 15min. In the process, a pressure-rising rate is 2.5MPa per sec and the pressure reduction time is 15sec.

Description

Method for improving shelf life of oysters by ultra high pressure treatment {Method for shelf-life extension of oyster by high hydrostatic pressure treatment}

1 is a diagram showing the change in enteritis vibrio bacteria of oysters treated with ultra high pressure for 10 minutes with different treatment pressures at room temperature (22 ° C.).

Figure 2 is room temperature (22 ℃), 150 Changes in enteritis vibrio bacteria in oysters treated with ultra high pressure with different treatment times from 5 to 30 minutes in MPa.

3 is 100 Changes in enteritis vibrio bacteria in oysters treated with ultra high pressure by varying the treatment temperature from 0 ° C to 10 ° C in MPa.

Figure 4 is a 150 ~ 400 treatment pressure at room temperature (22 ℃) It is the change of the coliform count of the oyster which was treated with ultra high pressure for 15 minutes by different MPa.

5 shows processing pressure 300 This is a diagram showing the change of E. coli bacteria in oysters treated with ultra high pressure by varying the treatment temperature at 0, 10, 22 ℃ in MPa.

Figure 6 is fixed at a processing temperature of 10 ℃ 350 It is the change of E. coli count of oysters treated with ultra high pressure by varying the treatment time from 5 to 25 minutes in MPa.

Figure 7 is a change in the total number of bacteria during 10 ℃ storage of untreated oysters and ultra high pressure treated oysters.

8 is a change in the lactic acid bacteria number of 10 ℃ storage of untreated oysters and ultra high pressure treated oysters.

9 is a change in pH of 10 ℃ storage of untreated oysters and ultra high pressure treated oysters.

10 is a diagram showing the change of volatile basic nitrogen during 10 ℃ storage of untreated oysters and ultra high pressure treated oysters.

The present invention relates to a method for improving shelf life of oysters by ultra-high pressure treatment, and relates to a method for increasing shelf life of oysters by sterilizing microorganisms by treating ultra-high pressure with oysters and improving storage period while maintaining the quality of oysters.

Oysters are a treasure trove of nutrients, so they contain a balanced amount of nutrients. It is called 'the milk of the sea' and is well received as an excellent nutritional food. The approximate composition of oyster meat is 76.0% of water, 11.6% of crude protein, 1.8% of crude fat, 2.3% of ash, and 5-8% of the rest as glycogen. Oysters also contain glycogen, iron, taurine, selenium, carotenoids, amino acids, and vitamins. have.

On the other hand, oysters are easily deteriorated and have a short shelf life even in refrigerated conditions. In particular, the meat tissue is softer than other shellfish and has a characteristic of being easily digested and digested, so that the utilization efficiency of the protein is high, but quality deterioration occurs quickly due to inappropriate temperature conditions during processing and distribution. In addition, microbial contamination and nutrients are destroyed during distribution, as well as loss of taste, color, and flavor due to enzymatic activity, resulting in shorter shelf life and difficult distribution conditions.

Genus Lactobacillus to reduce the pH as Pseudomonas species (Pseudomonas) and Vibrio genus (Vibrio), a Gram-positive carbohydrase strains producing the amine and ammonia major microorganism as a gram-negative proteolytic strains involved in the decay of the excavator (Lactobacillus) There is this.

Recently, the high-pressure processing method has attracted attention as a non-thermal processing method, because it can maintain the quality of the original product by minimizing changes in flavor, texture, and nutrients while sterilizing microorganisms and inactivating enzymes at room temperature. to be.

Until now, research on the ultrahigh pressure treatment of oysters has been mainly aimed at sterilizing Vibrio genus. Since Vibrio genus is relatively sensitive to high pressure and sterilized with 1 ~ 3 minutes of treatment at room temperature / 250 ~ 350 MPa, most studies focused on the quality change during storage by treating ultra high pressure with oyster under relatively mild sterilization conditions of Vibrio genus.

On the other hand, Escherichia coli is known to be sterilized under higher ultra-high pressure treatment conditions, and oysters grown in Korea cannot be ruled out because of the possibility of contamination by sewage from land.

Therefore, Vibrio parahaemolyticus as a suitable ultrahigh pressure sterilization method In addition, there is a method of improving shelf life of oysters treated under the treatment conditions that can be sterilized to E. coli. Was required.

The present invention has been made to solve the above problems, in addition to enteritis vibrio among pathogenic or decaying microorganisms by performing ultra-high pressure treatment to oysters To sterilize E. coli to maintain the quality of the oysters while providing an optimal storage method through the optimal ultra-high pressure treatment conditions that can enhance the shelf life.

Storage method of oysters by the ultra-high pressure treatment method according to the present invention for achieving the above object, in the storage method of the oyster ultra high pressure treatment including enteritis vibrio and Escherichia coli, the ultra-high pressure treatment of the oyster is temperature 0 ℃ -22 ℃, pressure 100-400 MPa, it is carried out in 5 to 45 minutes of time.

In addition, in the method of improving shelf life of the oyster by the ultra-high pressure treatment according to the present invention, the pressure rise rate is 2.5 MPa per second, the time taken for decompression is characterized in that 15 seconds.

In addition, in the method for improving storage of oysters by the ultrahigh pressure treatment according to the present invention, the ultrahigh pressure treatment of the oyster is preferably performed at a temperature of 22 ° C. and a pressure of 350 MPa is characterized in that it is carried out for 15 minutes.

In addition, in the method for improving storage of oysters by the ultrahigh pressure treatment according to the present invention, the ultrahigh pressure treatment of the oyster is preferably performed at a temperature of 10 ° C. and a pressure of 350 MPa is characterized in that it is carried out for 15 minutes.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The following examples illustrate the invention, and it is apparent to those skilled in the art that the scope of the invention is not limited thereto.

<Oyster>

Oysters ( Crassostrea gigas ) were collected from shell farms in Hansan Bay, Tongyeong, Gyeongnam (7.2 0.5 0.5 cm in length, 10.5 2.5 2.5 g in weight) and purchased at December 2004 and stored at -20 ° C.

<Strains and Medium Used>

Enteritis vibrio ( V. parahaemolyticus, ATCC 17802) and Escherichia coli ( E. coli, ATCC 8739) as the strain used in the Example were used by the Korea Institute of Science and Technology. Enteritis vibrio was used as a growth medium for bacteria by adding 2% NaCl to tryptic soy agar (Difco, USA), and E. coli was incubated at 35 ° C incubator using EC medium (Difco, USA) and agar, respectively. Incubated for 18 hours.

<Inoculation and culture method of enteritis vibrio and E. coli>

100 g of raw oysters and 50 mL of sterile artificial seawater were added to a sterile polypropylene bottle, and the stock culture 1 platinum was inoculated into a liquid medium, and then 1 mL of the bacterial culture incubated at 35 ° C. for 18 hours was added to a 30 ° C. incubator. Enteritis Vibrio was incubated for 24 hours and Escherichia coli for 18 hours. The composition of artificial seawater was the same as 400 mM NaCl, 100 mM MgSO ₄ ㅇ 7H ₂ O, 20 mM KCl, 20 mM CaCl _{2 ·} 2H ₂ O.

<Ultra High Pressure Treatment and Storage Experiment>

A polypropylene bottle containing oysters cultured with enteritis vibrio or Escherichia coli was placed in a high pressure vessel (55 x 5.1 cm) of an ultrahigh pressure apparatus (MFP-7000, Mitsubishi, Japan) and subjected to ultra high pressure, where distilled water was used as the pressure medium. Ultra high pressure treatment of oyster cultured enteritis vibrio temperature 0, 10, 22 ℃, pressure 100-300 MPa, time 5-30 minutes, ultra high pressure treatment of oyster cultured Escherichia coli temperature 0, 10, 22 ℃, pressure 150 It carried out at -400 MPa and time 5-45 minutes. The rate of pressure rise was 2.5 MPa per second and the time to depressurize was 15 seconds.

The ultrahigh pressure treatment conditions for the hypotonic test were room temperature (22 ℃) / 350 MPa / 15 minutes and 10 ℃ / 350 MPa / 15 minutes. The untreated sample and the ultra-high pressure sample were stored at 10 ° C. for 14 days and the number of microorganisms and quality change were measured.

<Microbial bacteria count>

<Bacterial count of enteritis vibrio and Escherichia coli>

Oysters were placed in a sterile plastic pack and 50 mL of sterile artificial seawater was added and ground in a back mixer (Bag Mixer, model 400, Interscience, France) for 5 minutes at a rate of 6 strokes / sec. Used as a sample for. Enteritis Vibrio used TCBS (Difco, USA) with 2% NaCl and EC agar (Difco, USA) as a medium, and plated 0.1 mL of diluted solution and incubated at 35 ° C for 24 hours to count viable cells. It was.

Total bacterial count, low temperature bacterial count and lactic acid bacteria count

The microorganisms in the oysters were measured by the standard plate culture method (Korea Food Industry Association, 2000). Total and low temperature bacteria were incubated for 48 hours at 35 ℃ and 25 ℃ in standard agar medium. The lactic acid bacteria were incubated at 37 ° C / 72 hours in Rogosa SL agar medium with 0.133% acetic acid adjusted to 5.5, and the colonies were counted using 30 to 300 colonies. The number of microorganisms per unit volume was calculated by multiplying. Three replicate measurements were taken and averaged.

<Quality measurement>

Oyster's pH

100 mL of distilled water was added to 10 g of crushed oysters and mixed. The mixture was ground for 3 minutes at a rate of 6 strokes / sec in a back mixer (model 400, Interscience, France) and measured with a pH meter (Corning, NY, USA).

<Volatile basic nitrogen>

5 g of oysters were taken in a centrifuge tube, and 25 mL of distilled water and 5 mL of 20% TCA were added, followed by centrifugation at 3,000 rpm for 20 minutes. The supernatant was filtered through filter paper (Toyo No. 5A), and 50 mL of 2% TCA was used as a sample. 1 mL of boric acid absorbent was added to the inner chamber of the Conway microdiffusion container, and 1 mL of saturated K ₂ CO _{3 and} 1 mL of sample were added to the outer chamber, and the cover was immediately covered with a clip. The micro-diffusion vessel was tilted from side to side and rotated to mix the K ₂ CO ₃ saturated solution with the sample in the outer chamber. This was left in an incubator at 30 ° C. for 2 hours and then titrated with 0.1 N HCl.

<Sensory test>

Sensory tests for oysters and immersion were conducted in accordance with the standards of food additives, etc. (Ministry of Health, Labor and Welfare, 1984) in Japan for odor, color of oyster, condition of oyster, color of immersion and state of immersion. It was conducted for the people. The demerit points were scored for each quality characteristic using the 3-point scale (0-2). The lower score means higher quality.

<Statistical processing>

The experimental results were statistically analyzed using SAS package (SAS, 1996), and analyzed by Duncan's multiple range test, and significance test was performed at α = 0.05.

<Variation of Enteritis Vibrio Cells According to Treatment Pressure>

In order to measure the effect of treatment pressure on the sterilization of enteritis vibrio inoculated into live oysters, the variation in the number of oysters treated with ultrahigh pressure for 10 minutes at 100 to 300 MPa at room temperature (22 ° C) was as shown in FIG. . The initial culture number of untreated oysters was 3.8 × 10 ⁵ CFU / mL. As the treatment pressure increased, the bacterial count gradually decreased to about 2 log cycles up to 175 MPa, but rapidly decreased at higher pressures. Killed.

<Changing bacterial count of enteritis vibrio with treatment time>

In order to measure the effect of treatment time on the sterilization of enteritis vibrio inoculated into live oysters, the variation in the number of bacteria of ultrahigh pressure treated oysters at 5 to 30 min at room temperature (22 ° C) and 150 MPa is shown in FIG. It was like The initial culture number of untreated oysters was 1.8 × 10 ⁵ CFU / mL, which decreased by about 2 log cycles until 10 minutes of treatment time, and continued to decrease with the increase of treatment time.

<Changing bacterial count of enteritis vibrio according to treatment temperature>

In order to measure the effect of the treatment temperature on the sterilization of enteritis vibrio inoculated in live oysters, the change in the number of bacteria in the ultrahigh pressure oyster treated with different treatment temperatures at 0 and 10 ° C. at 100 MPa was as shown in FIG. 3. The initial culture number of the untreated oysters was 3.4 × 10 ⁵ CFU / mL. As in the case of treatment at room temperature, the number of bacteria decreased with increasing treatment time at each treatment temperature. At the same treatment pressure and treatment time, the lower the treatment temperature, the higher the killing rate of microorganisms. When 20 and 25 minutes were treated at 100 MPa / 0 ° C and 10 ° C, respectively, they were completely killed. Therefore, the treatment time required to kill enteritis vibrio was further reduced by lowering the treatment temperature.

<Changes in the E. coli bacteria according to the treatment pressure>

In order to measure the effect of the treatment pressure on the sterilization of E. coli cultured inoculated into the live oysters, the variation in the number of oysters treated with ultra-high pressure for 15 minutes at 150 to 400 MPa at room temperature (22 ℃) was as shown in FIG. The initial culture number of the untreated oysters was 4.0 × 10 ⁷ CFU / mL, but there was little change in the number of bacteria up to 250 MPa, but it decreased sharply at higher pressures. It was reduced by about 3 log cycles with 275 MPa treatment and drastically decreased with increasing treatment pressure. It was reduced by about 5 log cycles with 325 MPa treatment.

<Changes in the number of bacteria of E. coli by treatment temperature>

In order to measure the effect of the treatment temperature on the sterilization of E. coli cultured inoculated into live oysters, the change in the number of cells of the oysters treated with ultra-high pressure at the treatment pressure of 300 MPa at 0, 10, 22 ℃ was as shown in FIG. The initial culture number of untreated oysters was 1.1 × 10 ⁷ CFU / mL. The lower the treatment temperature at the same treatment pressure and treatment time, the higher the sterilization effect. E. coli was sterilized after 25 and 35 minutes of treatment at 0 ℃ and 10 ℃, respectively, but it was not completely sterilized after 45 minutes of treatment at 22 ℃ .Reducing the treatment temperature required a short time for ultra-high pressure sterilization of E. coli. .

<Changes in the number of bacteria of E. coli by treatment time>

There is no legal regulation on the shelf life of raw oysters in Korea, but in Japan, the shelf life of raw oysters is set at 10 ℃ for 4 days. Therefore, as a result of the experiment on the sterilization effect of E. coli according to the treatment temperature, the sterilization effect is larger at 10 ℃ than at 22 ℃, so the treatment temperature is set to 10 ℃ to minimize the quality change during the processing. Of course, at 0 ℃, the effect of ultra high pressure sterilization is higher than at 10 ℃, but the treatment temperature was set to 10 ℃ in consideration of the increase in available cost due to low temperature treatment and the regulation of the distribution temperature and duration of oysters in Japan.

In order to measure the effect of the treatment time on the sterilization of E. coli inoculated into live oysters, the change in the number of bacteria in the ultrahigh pressure treated oysters was fixed by changing the treatment temperature to 10 ° C and changing the treatment time from 5 to 25 minutes at 350 MPa. It was like The initial culture number of untreated oysters was 7.2 × 10 ⁷ CFU / mL, and the number of bacteria decreased rapidly with the increase of treatment time, about 4 log cycles were reduced by 5 min treatment at 350 MPa and the detection limit was longer than 15 min. It became as follows.

In order to sterilize Escherichia coli inoculated from the above results, it was preferable to treat at 10 ° C./350 MPa / 15 minutes. If the raw oysters are treated under this condition, enteritis vibrio is also sterilized, so that pathogenic microorganisms can be killed through ultra-high pressure treatment. Hygiene safety is expected to be secured by the consumption of raw oysters.

<Changes in Total Bacteria and Lactic Acid Bacteria During Storage of Ultrahigh Pressure Raw Oysters>

The total bacterial counts of untreated oysters and ultra-high pressure treated oysters (350 MPa / 15 min) during storage at 10 ° C. were as shown in FIG. 7. The initial total bacterial count of untreated oysters was 1.6 × 10 ² CFU / mL, which increased rapidly during the storage periods, and at 4, 8 and 14 days of storage, respectively. 5.6 × 10 ⁴ , 7.5 × 10 ⁷ , and 7.3 × 10 ⁸ CFU / mL. Ultra high pressure treatment oyster decreased about 1 log cycle by the initial total germ number of ultra-high pressure treatment at about 10 ¹ CFU / mL, not large increase in the number of bacteria during storage period storage 7 days to was maintained at about 10 ³ CFU / mL or less After 14 days of storage, it was about 10 ⁵ CFU / mL. During 4 days of storage at 10 ° C., the untreated group had a 2 log cycle increase of about 10 ⁴ CFU / mL, while The ultra-high pressure treatment group was similar to the untreated group 4 days after 14 days of storage.

The changes in the number of lactic acid bacteria during 10 ° C. storage of untreated oysters and ultra high pressure treated oysters were shown in FIG. 8. Lactobacillus was not initially present in untreated oysters, but it began to be detected after 2 days of storage, and increased rapidly starting at 3.3 × 10 ³ CFU / mL on day ^{3 of} storage. 7.2 × 10 ⁴ , 7.7 × 10 ⁷ , 1.1 × 10 ⁹ CFU / mL. The ultrahigh pressure treated oysters were not detected by lactic acid bacteria until 4 and 5 days of storage, but were detected afterwards at about 10 ² and 10 ³ CFU / mL on days 8 and 14, respectively. Enteritis vibrio and Escherichia coli were not detected before and after ultrahigh pressure treatment and throughout storage.

The U.S. Food and Drug Administration has defined a standard aerobic microbial count of <500,000 CFU / g for bipods such as oysters, and substandard quality for> 1,000,000 CFU / g. According to the results of the experiment, the total bacterial count was greater than 10 ⁶ CFU / mL from the 5 days of storage, but the ultra-high pressure treated group showed 10 ⁵ CFU / mL even after 14 days of storage. The low-temperature bacterial count was more than 10 ⁶ CFU / mL in the untreated group from 5 days of storage, but the ultra-high pressure treated group was about 10 ⁵ CFU / mL even on the 10th day of storage, and showed 10 ⁶ CFU / mL after 14 days of storage. Lactic acid bacteria-free group was more than 10 ⁶ CFU / mL from day 5 storage, but the ultra-high pressure treatment group showed about 10 ³ CFU / mL even on day 14 storage. From the above results, it can be seen that the treatment of oysters with ultra high pressure has a significant effect on the inhibition of growth of total bacteria and lactic acid bacteria compared to the untreated group, which can delay the growth of microorganisms during the storage period.

Oyster's pH

Changes in pH during oyster storage are important indicators of quality change.In general, shellfish, unlike fish and other shellfish, have a high chemical content, especially high carbohydrate (glycogen) content and low total nitrogen content. Oyster rot caused by relatively high content of carbohydrate (glycogen) and gradually decreased in pH due to the accumulation of organic acid through fermentation process. . The initial pH of untreated oysters was 6.19, which continued to decrease during storage, at 5.83, 5.61, and 4.44 at 4, 8 and 14 days, respectively. The pH of oysters treated with ultra high pressure was 6.26 and 6.19, respectively, and there was almost no change by ultra high pressure treatment, and the pH change was very small during storage. The values were very high at 6.07, 6.03, and 5.82. From the above results, untreated oysters had a pH of 5.8 or less after 5 days of storage, whereas ultra-high pressure treated oysters maintained a pH of 5.82 even after 14 days of storage, and stored even when treated at room temperature (22 ° C). Up to 12 days, the pH was maintained almost the same.

<Volatile basic nitrogen>

Changes in volatile basic nitrogen during storage of untreated oysters and ultrahigh pressure treated oysters were shown in FIG. 10. The initial volatile basic nitrogen of untreated oysters was 16.8 mg%, which remained unchanged until day 1 and increased rapidly thereafter, and increased to 30.1, 43.4 and 60.7 mg% at days 4, 8, and 14, respectively. It was found that it was corrupting and could detect corruption. On the other hand, volatile basic nitrogen of oysters treated with ultra high pressure did not change very much during storage, so it was about 20 and 23 mg% on 4th and 8th day of storage, respectively, and it showed the value corresponding to fresh fish meat. there was. Even after 14 days, volatile basic nitrogen of oysters treated with ultra high pressure at 10 ° C and 22 ° C was not significantly increased to 27.6 and 32.2 mg%, respectively.

<Sensory test>

In order to compare the sensory quality of oysters and immersion, the smell, color of oyster, condition of oyster, color of immersion, and condition of immersion in accordance with Japanese food and additive standards (Ministry of Health, Labor and Welfare, 1984) The results obtained for the measurements were shown in Table 1. In the sum of Demerit scores, thawed fresh oysters showed the lowest scores, followed by ultra high pressure treatment at 10 ° C, followed by oysters stored at 10 ° C for 4 days, and oysters stored for 8 days, without ultra-high pressure treatment. Raw oysters stored for 4 days showed the highest score. As such, the ultrahigh pressure treated oysters were found to maintain a higher quality than the untreated 4 days of oysters even after 4 days and 8 days of storage at 10 ° C., thereby increasing the storage period more than twice by ultra high pressure treatment.

Table 1. Demerit scores of fresh oysters (4 days, 8 days storage at 10 ° C after 10 ° C / 350 MPa / 15 min treatment)

 parameter No treatment process Storage period (days) Storage period (days) 0 4 4 8 smell 0.25 ^c 1.33 ^a 0.83 ^b 0.92 ^b Color 0.54 ^b 1.38 ^a 1.33 ^a 1.21 ^a Meat t 0.54 ^c 1.71 ^a 1.08 ^b 1.17 ^b Color of immersion 0.71 ^b 1.50 ^a 1.42 ^a 1.46 ^a Viscosity of immersion 0.67 ^b 1.34 ^a 0.96 ^b 1.00 ^ab demerit score total 2.71 ^c 7.26 ^a 5.62 ^b 5.76 ^b

Although the present invention has been described in detail only in the specific embodiments described, it will be apparent to those skilled in the art that various modifications and variations are possible within the technical spirit of the present invention, and such modifications and modifications belong to the appended claims.

As described above, according to the present invention, by performing ultra-high pressure treatment on oysters, sterilization of Escherichia coli in addition to enteritis vibrio among pathogenic or decaying microorganisms has the advantage of maintaining the quality of the oysters while enhancing the shelf life as much as possible.

Claims (4)

In the method of improving shelf life by ultra-high pressure treatment of oysters containing Vibrio parahaemolyticus and Escherichia coli , The ultrahigh pressure treatment of the oyster is a temperature 0 ℃ to 22 ℃, pressure 100 ~ 400 MPa, carried out in a time of 5 to 45 minutes, the storage method of oysters by ultra-high pressure treatment. The method of claim 1, The pressure rise rate is 2.5 MPa per second, the decompression time is 15 seconds, characterized in that the storage method of the oyster by ultra-high pressure treatment. The method according to claim 1 or 2, Ultra-high pressure treatment of the oyster is a storage method of the oyster by the ultra-high pressure treatment, characterized in that carried out for 15 minutes at a pressure of 350 MPa at a temperature of 22 ℃. The method according to claim 1 or 2, The ultra high pressure treatment of the oyster is a storage method of the oyster by the ultra-high pressure treatment, characterized in that carried out for 15 minutes at a pressure of 350 MPa at a temperature of 10 ℃.

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