AU681518B2 - Process for the sterilization of food - Google Patents

Description

AUSTRALIA

Patents Act 1990 CONPLETE SPECIFICATION STANDARD PATENT Applicant: KUREHA KAGAKU KOGYO KABUSHIKI KAISHA Invention Title: PROCESS FOR THE STERILIZATION OF FOOD The following statement is a full description of this invention, including the best method of performing it known to me/us: V .0% 0 -1 TITLE OF THE INVENTION PROCESS FOR THE STERILIZATION OF FOOD BACKGROUND OF THE INVENTION The present invention relates to a process for the sterilization of food, and more specifically, a process for the sterilization of food free from the problems of giving an adverse effect to food taste and of causing the emission of foreign odor.

Foods are generally under the risk of microbial contamination and putrefaction, which may remarkably diminish the food values and, what is worse, may be responsible for the toxicosis by pathogenic bacteria. In order to apply to the wide distribution and the mass sale of recent years, it is naturally required to protect foods from the deterioration by bacteria and also to assure the food safety on the hygienic considerations. Accordingly, various sterilization processes have been proposed for improving the preservability of foods.

In Japanese Patent Publication (KOKOKU) No. 51-45660 (1976), for instance, a sterilizing composition comprising an organic acid and a salt thereof alone or in the form of a mixture thereof is disclosed. On the other hand, Japanese Patent Laid-Open (KOKAI) No. 2-60543 (1990) (USP No. 4,983,411) describes a sterilization process for vacuum-packaged raw meat comprising vacuum-packaging the raw meat in a heat shrinkable, ultraviolet transmissive packaging film, exposing the obtained package to ultraviolet light and then treating said package in a high-

Y~

-2temperature atmosphere for achieving both the sterilization of said package and the shrinkage of said packaging film.

However, the sterilizing composition described in the Japanese Patent Publication (KOKOKU) No. 51-45660 cannot be escaped from the problem of giv:.ng an adverse effect to food taste, since the composition needs to be used at a high concentration. Whereas, the sterilization process described in the Japanese Patent Laid-Open (KOKAI) No.

2-60543 (1990) is not always satisfactory. In particular, at an ultraviolet irradiation dose of 2000 mW-sec/cm 2 or more, further improvement of the sterilizing effect cannot be expected and, depending upon the products to be sterilized, such high ultraviolet irradiation dose may cause the emission of foreign odor.

The present inventors have found that the problems of giving an adverse effect to food taste and of causing the emission of foreign odor can be avoided by a particular combination of a treatment with an organic acid and a treatment with ultraviolet light. The present invention *e has been achieved based on this finding.

SUMMARY OF THE INVENTION In an aspect of the present invention, there is provided a process for the sterilization of a food, which comprises treating a food with an organic acid, and S exposing the treated food to ultraviolet radiation.

DETAILED DESCRIPTION OF THE INVENTION Foods which may be treated according to the present invention are various kinds of dressed meat including beef, pork, chicken, mutton, fish and the like. And, in addition thereto, processed meat including ham and sausage as well as chikuwa (baked fish paste shaped in hollow cylindrical form) and kamaboko (boiled fish paste shaped in solid semicylindrical form on a small wooden plate) may also be suitably treated. Dressed meat as well as the processed meat such as ham and sausage are particularly preferred.

On the other hand, examples of organic acids which may be used are those having a carboxylic group and include acetAc acid, fumaric acid, citric acid, succinic acid, malic acid, lactic acid, tartaric acid, gluconic acid and the like.

Among these organic acids, acetic acid or lactic acid may be preferably used.

According to the sterilization process of the present invention, foods are treated first with an organic acid.

The organic acid is usually used in the form of an aqueous solution and the concentration thereof may be 1 to 500 mM.

According to the present invention, the synergism between •the treatment with organic acid and the treatment with ultraviolet light may produce an excellent sterilizing effect as described below, hence the concentration of S' organic acid may be sufficient in the lower side of the above range. Consequently, the sterilization process of the present invention is escaped from the problem of giving an adverse effect to food taste. The concentration of the l organic acid may be preferably 2 to 70 mM, more preferably to 40 mM.

Treatment with organic acid may be conducted by any of various known ways such as coating, spraying, or dipping.

i 'P 1__1 I~ -4- According to the present invention, foods which had been treated with organic acid are treated with ultraviolet light. In such case, it is preferred that foods which had been treated with organic acid are film-packaged prior to the treatment with ultraviolet light, because there would occur the risk that the foods under treating in the production line might be reattached by bacteria between the treatment with organic acid and the treatment with ultraviolet light as well as between the latter and the packaging, hence resulting in the decrease of sterilizing effect.

The film may be any of those which are commonly used for food packaging, in so far as it is transmissive to ultraviolet light. Examples thereof are uni- or bi-axially stretched films of polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, ethylene-vinyl acetate copolymer, nylon, polyethylene, ionomer, polypropylene, polyester, and the like, which may be used in the form of a single film or a composite film composed of two or more of those materials mentioned above. Films having an ultraviolet transmission .(wavelength of 253.7 nm) of 50% or more are usually used.

Packaging processes may be those which are conventionally used for packaging foods. Examples thereof are inert gas charge packaging, skin pack packaging, deep draw vacuum packaging, in-line close packaging, off-line close packaging, vacuum packaging, vacuum shrink packaging, and the like. When shrinkable films are used, the films may be subjected to heat treatment for shrinkage. Heat i I rPCPI ~-SC treatment may be performed by means of hot water bath, hot water shower, steam injection, and the like.

The present invention is characterized in that foods are treated with ultraviolet light after treated with organic acid. By treating in the specific sequence as defined above, an excellent sterilizing effect may be obtained as the result of the synergism between organic acid and ultraviolet light. In contrast thereto, when foods are treated with organic acid after treatment with ultraviolet light, no synergistic effect may be observed.

Treatment with ultraviolet light may be conducted by means of any of commercially available ultraviolet sterilizing apparatuses. Ultraviolet light belonging to the UV-C region (100 to 280 nm) may be preferably used.

The ultraviolet irradiation dose (intensity x time) may be usually 5 to 1200 mW-sec/cm 2 and preferably 8 to 800 mW-sec/cm 2 At a dose of less than 5 mW-sec/cm 2 the sterilizing effect may be unsatisfactory, whereas at a dose of more than 1200 mW-sec/cm 2 a further improvement of the sterilizing effect cannot be expected. In addition, there might be detected the emission of foreign odor depending "upon the products to be treated.

Particularly preferred is the process wherein the treatment with ultraviolet light is conducted subsequent to the film packaging of the food which has been previously treated with organic acid, since such sequential process erables to protect the food from the contamination by bacteria both before and after the treatment with -L II I- -6ultraviolet light, while keeping the respective effects of organic acid and ultraviolet light.

According to the present invention described as above, owing to the synergism between the treatment with organic acid and the treatment with ultraviolet light, a higher sterilizing effect may be obtained in comparison with the case in which either the tre at-ent with organic acid or the treatment with ultraviolet light is solely applied, by using the concentration of organic acid and the irradiation dose of ultraviolet light respectively at lower values than those which are used in the latter case. Consequently, according to the present invention, it is provided a process for the sterilization of food, which is improved so as to avoid the problems of giving an adverse effect to food taste and of causing the emission of foreign odor.

EXAMPLES

The present invention will now be described in more S" detail with reference to examples, which should be considered by no means limitative without departing from the spirits of the present invention.

Example 1 To each of aqueous lactic acid solutions having concentrations of 0 to 100 mM, Escherichia coli (IAM1253) was added to obtain a suspension containing 1.5 x 104 cells/ml. A slice of boneless ham having a surface area of cm x 10 cm was inoculated with 0.3 ml of the above suspension. Then, with a multilayered film of polyvinylidene chloride, the slice was vacuum-packaged c under the conditions of a dial of 4 and a time of seconds in a Multivac model A-300 vacuum-packaging apparatus to obtain a packaged sample.

The multilayered film of polyvinylidene chloride was composed of an outermost layer of linear ultra low-density polyethylene, an outer layer of ethylene-methacrylic acid copolymer, a core layer of polyvinylidene chloride, an inner layer of ethylene-methyl acrylate copolymer, an innermost layer of linear ultra low-density polyethylene and an adhesive layer of ethylene-vinyl acetate copolymer (compositional mass ratio of 85:15). This film had the total thickness of 55 jim and an ultraviolet transmittance (wavelength of 253.7 nm) of The above packaged samples were exposed to ultraviolet radiation (wavelength of 253.7 nm) at various transmitted doses in the range of 0 to 800 mW-sec/cm 2 ("transmitted dose" means a dose of light which had transmitted a packaging film, that is, a dose of light which had reached the surface of the sample). Thereafter, the number of bacterium E. coli in each sample was counted. Counting of the number of bacterium E. coli was conducted according to a process in which the treated slice of boneless ham having a surface area of 10 cm xl0 cm was wiped with a gauze infiltrated with 1 ml of sterilized saline, then the gauze was washed out into 9 ml of sterilized saline, thereafter the number of bacterium E. coli in the resulting saline was counted by conventional procedure. The results are shown in Table 1.

Table 1 Transmitted dose of ultraviolet Concentration of lactic acid (mM) light (mW-sec/cm 2 0 10 50 100 <Number of bacteria (X103)> 0 4.40 3.60 0.032 <0.009 8 2.70 0.26 0.018 <0.009 24 2.50 0.19 0.009 <0.009 1.00 0.14 <0.009 <0.009 96 0.77 0.11 <0.009 <0.009 320 0.66 0.09 .009 <0.009 800 0.60 0.06 <0.009 <0.009 note: a concentration of 0 mM and a transmitted dose of ultraviolet light of 0 mW-sec/cm 2 both indicate the untreated (The same shall appxy hereinafter).

As is clear from the above results, the combination of the treatments respectively using lactic acid and ultraviolet light is effective at a lower transmitted dose than that which is us-d when only the treatment with .ultraviolet light is applied. In addition, sterilizing effect is remarkably improved.

When only the treatment with ultraviolet light was applied at a transmitted dose of 8 mW-sec/cm 2 the effect decreasing the number of bacterium E. coli by an order of magnitude could not be observed, and when the transmitted dose was increased to a value of 96 mW-sec/cm 2 the effect enabling a decrease by one order of magnitude (about in the number of bacteria was observed. On the other hand, when only the treatment with lactic acid was 'IC ~e -9applied at a concentration of 10 mM, the effect decreasing the number of bacterium E. coli by an order of magnitude was not observed. On the contrary thereto, when a sample was treated sequentially with lactic acid at a concentration of 10 mM and with ultraviolet light at a transmitted dose of 8 mW-sec/cm 2 the effect enabling a decrease by one order of magnitude (about 10-fold) in the number of bacterium E. coli was observed. Moreover, when a sample was treated sequentially with lactic acid at a concentration of 10 mM and with ultraviolet light at a transmitted dose of 320 mW-sec/cm 2 the effect enabling a decrease by two orders of magnitude (about 100-fold) in the number of bacterium E. coli was observed.

In either case, there was neither observed the emission of foreign odor nor the change of food taste.

Example 2 The sterilizing effect against E. coli was tested in a similar manner to that of Example 1, except that a suspension containing acetic acid and 1 x 104 cells/ml was used. The results are shown in Table 2.

o *eo oo *a go *oa *e*o* I i; i;i Table 2 Transmitted dose of ultraviolet Concentration of acetic acid (mM) light (mW-sec/cm 2 0 6 40 100 <Number of bacteria (X10 3 0 3.20 3.00 0.022 <0.009 8 2.10 0.19 0.012 <0.009 24 1.80 0.13 0.009 <0.009 0.72 0.10 <0.009 <0.009 96 0.58 0.098 <0.009 <0.0)9 320 0.28 0.085 <0.009 <0.009 800 0.21 0.057 <0.009 <0.009 As is clear from the above results, the combination of the treatments respectively using acetic acid and Sultraviolet light is effective at a lower dose than that which is used when only the treatment with ultraviolet light is applied. In addition, sterilizing effect is remarkably improved.

When only the treatment with ultraviolet light was applied at a transmitted dose of 8 mW-sec/cm 2 the effect decreasing the number of bacterium E. coli by an order of magnitude was not observed, and when the transmitted dose was increased to a value of 40 mW.sec/cm 2 the effect enabling a decrease by one order of magnitude (about in the number of bacteria was observed. On the other hand, when only the treatment with acetic acid was applied at a concentration of 6 mM, the effect decreasing the number of bacterium E. coli by an order of magnitude -11was not observed. On the contrary theret hen a sample was treated sequentially with acetic acid at a concentration of 6 mM and with ultraviolet light at a transmitted dose of 8 mW'sec/cm 2 the effect enabling a decrease by one order of magnitude (about 10-fold) in the number of bacterium E. coli was observed. Moreover, when a sample was treated sequentially with acetic acid at a concentration of 6 mM and with ultraviolet light at a transmitted dose of 96 mWsec/cm 2 the effect enabling a decrease by two orders of magnitude (about 100-fold) in the number of bacterium E. coli was observed.

In either case, there was neither observed the emission of foreign odor nor the change of food taste.

Example 3 The sterilizing effect against E. coli was tested in a similar manner to that of Example 1, except that chilled beef, ultraviolet light having a transmitted dose in the range of 0 to 640 mW'sec/cm 2 and an aqueous lactic acid solution having a concentration in the range of 0 to 10 mM were employed. The results are shown in Table 3.

e e *eoc -12- Table 3 Transmitted dose of ultraviolet Concentration of lactic acid (mM) light (mW-sec/cm 2 0 <Number of bacteria (x10 3 0 4.50 3.40 8 3.40 0.48 24 2.00 0.30 1.30 0.12 0.60 0.08 160 0.48 0.05 320 0.43 0.03 640 .0.38 0.02 As is clear from the above results, the combination of the treatments respectively using lactic acid and ultraviolet light is effective at a lower dose than that which is used when only the treatment with ultraviolet '*light is applied. In addition, sterilizing effect is remarkably improved.

When only the treatment with ultraviolet light was applied at a transmitted dose of 8 mW-sec/cm 2 the effect decreasing the number of bacterium E. coli by an order of magnitude was not observed, and when only the transmitted 00 dose was increased to a value of 80 mW-seccm 2 the effect enabling a decrease by one order of magnitude (about in the number of bacteria was observed. On the other hand, when only the treatment with lactic acid was applied at a concentration of 10 mM, the effect decreasing -13the number of bacterium E. coli by an order of magnitude was not observed. On the contrary thereto, when a sample was treated sequentially with lactic acid at a concentration of 10 mM and with ultraviolet light at a transmitted dose of 8 mW-sec/cm 2 the effect enabling a decrease by one order of magnitude (about 10-fold) in the number of bacterium E. coli was observed. Moreover, when a sample was treated sequentially with lactic acid at a concentration of 10 mM and with ultraviolet light at a transmitted dose of 80 mW-sec/cm 2 the effect enabling a decrease by two orders of magnitude (about 100-fold) in the number of bacterium E. coll was observed.

In either case, there was neither observed the emission of foreign odor nor the change of food taste.

Comparative Example 1 To saline, Escherichia coll (IAM1253) was added to obtain a suspension containing 9.3 x 103 cells/ml. Each piece of chilled beef having a surface area of 10 cm x cm was inoculated with 0.3 ml of the above suspension, then treated with ultraviolet light (wavelength of 253.7 nm) at a dose in the range of 0 to 400 mW-sec/cm 2 thereafter coated with 0.3 ml of an aqueous lactic acid solution having a concentration in the range of 0 to 10 mM.

Counting of the number of bacterium E. coli in each treat-ed sample was performed in a similar manner to that of Example 1. The results are shown in Table 4.

I

-14- Table 4 Dose of ultraviolet Concentration of lactic acid (mM) light (mW-sec/cm 2 0 <Number of bacteria (X103)> 0 2.80 2.30 400 0.55 0.51 As shown in the above results, when a sample was treated sequentially with ultraviolet light at a dose of 400 mW-sec/cm 2 and with lactic acid at a concentration of mM, the effect enabling a decrease by one order of magnitude (about 10-fold) in the number of bacterium E.

coli was observed. This effect was about the similar extent to that obtained by treating solely with ultraviolet light at a dose of 400 mW-sec/cm 2 The synergistic effect .o.e between the treatment with ultraviolet light and that with lactic acid was not perceived.

Example 4 S: Each piece of chilled beef having a surface area of cm x 10 cm was inoculated with the suspension used in Comparative example 1, then coated with 0.3 ml of an aqueous lactic ac d solution having a concentration of mM, thereafter treated with ultraviolet light (253.7 nm) at a dose of 400 mW-sec/cm 2 Counting of the number of bacterium E. coli was performed in a similar manner to that of Example 1. The result showed that the number of bacteria were 3.4 X10 1 indicating the effect enabling a decrease by two orders of magnitude (about 100-fold) in the number of bacterium E. coil. The synergistic effect between the treatment with ultraviolet light and that with lactic acid was perceived.

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Claims (6)

1. A process for the sterilization of food, comprising treating a food with an organic acid, and exposing the treated food to ultraviolet radiation.

2. A process for the sterilization of food, comprising treating a food with an organic acid, packaging the treated food with a film, and exposing the packaged food to ultraviolet radiation.

3. The process for the sterilization of food according to claim 1 or 2, wherein said organic acid is at least one selected from the group consisting of acetic acid, fumaric acid, citric acid, succinic acid, malic acid, lactic acid, tartaric acid and gluconic acid.

4. The process for the sterilization of food according to 4 claim 1 or 2, wherein said organic acid is acetic acid. o 0 *6.6 4

5. The process for the sterilization of food according to claim 1 or 2, wherein said organic acid is lactic acid, S6. The process for the sterilization of food according to claim 1 or 2, wherein said organic acid is used at a *o concentration of 2 to 70 mM.

7. The process for the sterilization of food according to 0 claim 1 or 2, wherein ultraviolet light is used at a dose per unit area of the food surface of 5 to 1200 mW-sec/cm 2 DATED THIS 03RD DAY OF JULY 1995 KUREHA KAGAKU KOGYO KABUSHIKI KAISHA By its Patent Attorneys: GRIFFITH HACK CO. Fellows Institute of Patent Attorneys of Australia Abstract PROCESS FOR THE STERILIZATION OF FOOD A process for the sterilization of food, comprising treating a food with an organic acid, and exposing the treated food to ultraviolet radiation. The treated food preferably packaged with a film prior to the ultraviolet radiation. ee* ii-l"il