Abstract:
Oxygen is a major quality-deteriorating factor with respect to many food products in that it may cause the growth of molds and the development of rancid off-flavors, which reduce the quality or shelf life of many food products. The present invention provides an improved food packaging and a method for prolonging the shelf life and quality of packaged foods by packaging the food in a packaging material together with a microbial oxygen absorber, such as  Lactococcus  spp.,  Streptococcus  spp.,  Lactobacillus  spp.,  Leuconostoc  spp.,  Brevibacterium  spp.,  Propionibacterium  spp., and  Bifidobacterium  spp.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to the fields of packaging materials, microbiology and methods for preserving food products. 
       BACKGROUND OF THE INVENTION 
       [0002]    A wide range of methods is used for preserving food products. Among these methods are the use of antimicrobial preservatives, e.g. chemicals such as nitrate, sulphur dioxide, benzoic acid, and proteins such as nisin and pediocin. Another method is the addition of an antioxidant such as ascorbic acid, citric acid and tocopherols. Antioxidants prevent oxidation of foods, which would otherwise result in rancidity and discoloration. 
         [0003]    EP 0 092 183 B1 discloses a method for preservation of food by providing a culture in the food containing lactose, which generates a bacterial spoilage inhibitory substance. 
         [0004]    WO 01/52668 discloses porphyrin-containing lactic acid bacteria and their use for reducing oxygen content in a food product. 
         [0005]    Oxygen is a major quality-deteriorating factor with respect to many food products. Oxygen may cause growth of molds and development of rancid off-flavors, which subsequently reduce the quality and shelf life of many food products. It is therefore desirable to reduce the oxygen content in the air having contact with the food product within the packaging. Packaging in modified atmospheres with low residual oxygen has been introduced in order to reduce the quality changes associated with the presence of oxygen. 
         [0006]    Presently the residual oxygen level in packaged foods may be reduced by means of the following approaches:
       Repeating vacuum and gas flushing cycles to reduce the residual oxygen content. This method is expensive both with respect to amounts of gas used and time used for the gas flushing cycles. Hence, significant increases in packaging costs result.   Use of a chemical oxygen absorber. The present systems utilize one or more of the following concepts: iron powder oxidation, ascorbic acid oxidation, photosensitive dye oxidation, enzymatic oxidation (e.g. glucose oxidase and alcohol oxidase), unsaturated fatty acids (e.g. oleic acid or linolenic acid), or immobilized yeast on a solid material (Vermeiren et al., 1999, 2003). Most of the currently commercially available chemical oxygen absorbers are based on iron powder oxidation. Additionally, enzymatic removal of oxygen has been proposed as a promising technique (Vermeiren at al., 1999, 2003). The oxygen absorbing materials are incorporated into labels, sachets, or into the packaging material. The disadvantages of these systems are that the absorber efficiency is often low and the time used before the system is activated is unacceptably long. Furthermore, legislative aspects in relation to food products in some cases hinder the use of these systems.       
 
         [0009]    Food products packaged in vacuum or with a modified atmosphere are susceptible to packaging defects, and oxygen enters the packaging on opening of the package during use. Furthermore, obtaining low residual oxygen content in the packaging process is time-consuming and costly. 
         [0010]    Thus, there is a need within the food industry to find alternative or supplementary ways of reducing the residual oxygen content in packaged foods. Such alternative ways of reducing residual oxygen content must comply with food regulatory legislation as well as with consumer preferences. 
       SUMMARY OF THE INVENTION 
       [0011]    Accordingly, the present invention provides a method for preservation of a food product by packaging said food in a packaging material together with a microbial oxygen absorber. 
         [0012]    Thus, in one aspect the invention is related to a food product packaged in a packaging material together with a microbial oxygen absorber. 
         [0013]    The present invention also provides growth media containing microorganisms capable of reducing the oxygen content in the package. The microbial oxygen absorber is preferably microorganisms consuming oxygen with little or no concomitant production of carbon dioxide and organic acids. An example of such a microorganism is a  Lactococcus lactis  strain, which uses oxygen and produces limited amounts of diacetyl and acetoin. 
         [0014]    In a preferred embodiment of the invention the microbial oxygen absorber is applied to the surface of the food. In another preferred embodiment of the invention the microbial oxygen absorber is applied to a sachet, label, capsule, or as freeze-dried pellets placed within the package in a way to minimize transfer of said microbial oxygen absorber onto said food. In another embodiment the microbial oxygen absorber is incorporated into the packaging material, e,g. in a laminated structure or a coating. In another aspect the present invention provides a food product, which has a low content of oxygen within the packaging even after the consumer has repeatedly opened the packaging. 
         [0015]    One advantage of the present invention is that increased packaging machine speed can be used because the residual oxygen at the time of packaging can be increased. Another advantage is that the oxygen content within the food packaging can be repeatedly decreased after opening and closing the packaging. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1   a  is a schematic illustration of the incorporation of a microbial oxygen absorber into a packaging material for food, 
           [0017]      FIG. 1   b  is a schematic illustration of the microbial oxygen absorber being sprayed on the surface of the packaging material facing the food, 
           [0018]      FIG. 1   c  shows an alternative application of a microbial oxygen absorber according to the invention, 
           [0019]      FIG. 2  shows the measured oxygen content in samples stored 0-20 days at 9° C. Dotted lines with white dots are samples without the microbial oxygen absorber. Solid lines with black dots are samples with the microbial oxygen absorber. Triple determinations. Consecutive measurements were performed on the same package throughout the experiment, and 
           [0020]      FIG. 3  shows measured oxygen content in samples stored 0-20 days at 20° C. Dotted lines with white dots are samples without the microbial oxygen absorber. Solid lines with black dots are samples with the microbial oxygen absorber. Triple determinations. Consecutive measurements were performed on the same package throughout the experiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]      FIG. 1   a  shows a perishable food product  10  stored within a packaging  20  comprising a shaped upper part  22  formed from a layered material  22 ′ and having a foil  28  bonded to a peripheral rim  26  thereof. As shown, a tray-like bottom part  27  may be snapped on to the rim  26 . 
         [0022]    The layered material  22 ′ of the upper part  22  may comprise three layers  23 ,  24 ,  25 , with an upper or outer layer  23  defining a barrier adapted to prevent in a conventional manner entry into the packaging  20  of air that would lead to a rapid decay of the food product  10  and thus reduce the period in which the product  10  will remain fresh prior to opening of the packaging  20  by removal of the foil  28 . The central or inner layer  24  of layered material  22 ′ is defined by or includes a microbiological oxygen absorbing material to be discussed in closer details below. A further layer  25  defines a surface of the packaging  20  facing the food product  10 , and layer  25  is permeable to allow gas communication between layer  24  and the inside of packaging  20 . 
         [0023]    Preferably, the material for the upper layer  23  and for the foil  28  comprises a PE layer to ensure sealing. The permeable layer  25  is preferably made from a perforated PE web. It is noted, however, that the packaging  20  may be made from glass or a metal, with the microbial oxygen absorber layer  24  applied on the inwardly facing surface thereof. The foil  28  may also be defined by a layered material having properties identical or similar to layered material  22 ′. In one embodiment, the packaging  20  may have regions, such as the sides  21  of the upper part  22 , where no microbial oxygen absorber is provided. 
         [0024]    In the embodiment shown in  FIG. 1   a,  the upper part  22  is made to retain a shape where a relatively large headspace  15  is defined between the food product  10  and the upper part  22 ; the upper part  22  may, however, be shaped such that the food product  10  fits lightly therein. 
         [0025]    It is noted that the layered material  22 ′ with the microbial oxygen absorber is preferably manufactured well in advance of the making of the packaging  20 ; however, in some cases, such as when the lifetime or activity of the microbiological oxygen absorbing material layer  24  is short or critical, it may be preferred to make the layered material  22 ′ immediately prior to the time when the packaging  20  is sealed by the foil  28 , thereby reducing the period of time where the material layer  24  is exposed to atmospheric air. 
         [0026]    The layered material  22 ′ may alternatively be formed without the permeable layer  25  where no protection or control of the activity of the microbiological oxygen absorbing layer  24  is required.  FIG. 1   b  shows one such example where layered material  22 ′ comprises an upper layer  23  as described above and carrying a layer of a microbial oxygen absorber sprayed or otherwise applied to the layer  23 . Such a layered material  22 ′ for the upper part  22  may be manufactured right before the upper part  22  is shaped such as by injection moulding or deep-drawing. 
         [0027]    In the above, the packaging  20  has been described above as providing a well-defined headspace  15  by the packaging  20  including a part  22  adapted to retain its shape under normal use. However, the use of a flexible packaging material including a microbiological oxygen absorbing material and wrapped around the food product  10  also falls within the general concept of the present invention. 
         [0028]      FIG. 1   c  shows an alternative embodiment of the invention where a layer  24  of a microbiological oxygen absorbing material has been applied to the surface of the food product  10 , the packaging  20  being made from any conventional gas-impermeable material adapted to prevent entry of air into the packaging  20 . The microbial oxygen absorbing material may be applied by spraying a slurry thereof onto the food product  10  before or during packaging. Optionally the slurry may comprise one or more nutrients for the microbial oxygen absorber, e.g. a carbon and/or nitrogen-source. When the food is a cheese, the application of the microbial oxygen absorber onto the cheese may be followed by the application on the food product  10  of a semi air-impermeable coating, e.g. Dutch plastic coating, paraffin wax or other lipid-based coatings. 
         [0029]    In yet another preferred embodiment (not shown) the microbial oxygen absorber may be applied to a separate sachet or label placed within packaging  20  of  FIG. 1   c,  or the microbial oxygen absorber, preferably as freeze-dried powder pellets, may be introduced into the packaging  20  before sealing thereof. When in liquid form, the microbial oxygen absorber may be injected into the packaging  20  by perforating the packaging  20  and then resealing. 
         [0030]    Food products  10  packaged according to conventional methods often perish rapidly due to oxygen present within the packaging, i.e. either in a headspace between the packaging and the food product or within the food product itself. Although the food products may be packaged in a vacuum or in a modified atmosphere, obtaining highly reduced low residual oxygen content in the packaging process is time-consuming and costly. 
         [0031]    The use of a microbial oxygen absorber material as mentioned above allows for a reduction of the residual oxygen content by the microbial oxygen absorber ensuring that the oxygen concentration within the packaging  20  continuously decreases, preferably until depletion, following closure of the packaging  20 . The invention is useful when the food product  10  is packaged in a vacuum or in a modified atmosphere and even when the food product  10  is packaged in atmospheric air. 
         [0032]    In addition, a prolonged lifetime of the food product  10  may be ensured through the effect of the microbial oxygen absorber material after opening of the packaging  20  by the consumer where access of atmospheric air to the interior of the packaging is no longer restricted. 
         [0033]    It is noted that, irrespectively of the packaging  20  selected for the food product  10 , the microbial oxygen absorber discussed herein may be incorporated into the food product itself during the production process of the food product, for the purpose of providing a prolonged lifetime of the food product, thus allowing for the use of any conventional packaging. 
         [0034]    The microbial oxygen absorber is preferably selected from microorganisms classified as GRAS microorganisms (Generally Recognised As Safe). Among microorganisms classified as GRAS are  Lactococcus  spp.,  Streptococcus  spp.,  Lactobacillus  spp.,  Leucnostoc  spp.,  Brevibacterium  spp.,  Propionibacterium  spp.,  Bifidobacterium  spp.,  Saccharomyces  spp., and  Kluyveromyces  spp. 
         [0035]    Many microorganisms use oxygen during their metabolism. Some, however, produce acids, alcohols, gases, and flavor compounds during this process, which may cause undesirable sensory and physical changes in the foods. In one embodiment of the invention the microbial oxygen absorber uses oxygen without subsequently reducing pH or producing significant amounts of gases. In another embodiment the microbial oxygen absorber is a microorganism that also produces a change in the flavour of the food product. This change of flavour of the food product may be desirable for some applications, e.g. in relation to some dairy products. 
         [0036]    In another embodiment of the invention the microbial oxygen absorber is selected from oxygen absorbing strains of  Lactococcus  spp.,  Streptococcus  spp.,  Lactobacillus  spp.,  Leucnostoc  spp.,  Brevibacterium  spp.,  Propionibacterium  spp.,  Bifidobacterium  spp. and yeast spp. In their natural form these species may not absorb oxygen fast enough and at low concentrations of oxygen as desired when using them as microbial oxygen absorbers according to the present invention. The oxygen consumption rate of microorganisms may be improved by changing the microorganisms by either cultural modifications, modification by introducing mutations or by other genetic modifications. 
         [0037]    The first option is to manufacture the microorganisms under conditions where they acquire or improve their ability to absorb (metabolize) oxygen. One way to accomplish this is to manufacture the microorganisms in a medium containing porphyrin, e.g. as haemin. Microorganisms may in this way be “loaded” with a porphyrin compound, allowing microorganisms which do not naturally contain porphyrin compounds or which contain insufficient porphyrin compounds, e.g.  Lactococcus,  to absorb oxygen. Reference is made to WO 01/52668 wherein a strain of  Lactococcus lactis  subsp.  lactis  (DSM 12015) was cultured in a medium containing haemin, thus resulting in bacteria containing at least 0.1 ppm on a dry matter basis of a porphyrin compound. 
         [0038]    Another option for modifying a microorganism such as a lactic acid bacterium, is to introduce one or more mutations causing a shift in the metabolism such that the oxygen absorption by metabolism is increased. In one embodiment a lactic acid bacterium is Ldh defective, Lch − , i.e. a mutation has been introduced which causes a defective lactate dehydrogene activity. Ldh −  strains cannot regenerate NAD +  from NADH by reducing pyruvate to lactic acid, and these strains must rely on other reactions for regenerating NAD + , e.g. NADH oxidase encoded by the nox gene. Regeneration of NAD+ by NADH oxidase causes the concomitant consumption of oxygen. Thus, in yet another embodiment the microbial oxygen absorber is a lactic acid bacterium having Ldh −  phenotype and overexpressing NADH oxidase. In yet another embodiment, the microbial oxygen absorber is a lactic acid bacterium having Ldh −  and Pfl −  phenotype, i.e. being defective in both lactate dehydrogenase and in pyruvate formate lyase activities. Methods for producing such Ldh −  strains are disclosed in WO 98/54337, EP 0937774 and EP 0928333. These documents also disclose assays suitable for quantification of the oxygen consumption rate by these microorganism. Typically, a liquid such as skimmed milk at 30° C. is inoculated with an appropriate amount of microorganisms, e.g. 10 7  CFU/mL, and the oxygen concentration in the liquid is measured over time. 
         [0039]    In yet another embodiment the microbial oxygen absorber is  Lactococcus lactis.  In yet another embodiment the microbial oxygen absorber is a  Lactococcus lactis,  which consumes oxygen and does not produce lactic acid. In yet another embodiment the microbial oxygen absorber is a  Lactococcus lactis  strain which is Ldh − , e.g. DN-224 (DSM 11037). In yet another embodiment the microbial oxygen absorber is a  Lactococcus lactis  strain which is Ldh −  and Pfl − , e.g. DN-223 (DSM 11036). In yet another embodiment the microbial oxygen absorber is a  Lactococcus lactis  strain which is Ldh −  and overexpresses NADH oxidase. 
         [0040]    In other embodiments the microbial oxygen absorber does not produce significant amounts of organic acids and carbon dioxide. In yet another embodiment the microbial oxygen absorber is  Lactococcus lactis  subsp.  diacetylactis.  In yet another embodiment the microbial oxygen absorber is a  Lactococcus lactis  subsp.  diacetylactis  strain which is Ldh + . In yet another embodiment the microbial oxygen absorber is a  Lactococcus lactis  subsp.  diacetylactis  which is Ldh −  and Pfl − . In yet another embodiment the microbial oxygen absorber is a  Lactococcus lactis  subsp.  diacetylactis  strain which is Ldh −  and overexpresses NADH oxidase. 
         [0041]    In another embodiment of the invention the microbial oxygen absorber is able to lower the concentration of oxygen in skimmed milk at 30° C. from about 8 mg/kg to less than 1 mg/kg in less than 3 hours after inoculating the skimmed milk with 10 6  CFU/mL of the microbial oxygen absorber. 
         [0042]    In another embodiment of the invention the microbial oxygen absorber is able to lower the concentration of oxygen in a solution of 0.1% peptone, 0.85% NaCl and 3% lactose at 30° C. from about 8 mg/kg to less than 1 mg/kg in less than 3 hours after inoculating the skimmed milk with 10 6  CFU/mL of the microbial oxygen absorber. 
         [0043]    A wide variety of food products may be preserved according to the present invention. Dairy products, such as cheese, are particularly preferred. In one embodiment of the invention the food product is selected from the group consisting of a sliced meat product, a ready meal incl. a sous-vide product, or a bakery product. 
         [0044]    The present invention is further illustrated by the following examples, which, however, are not to be construed as limiting the scope of protection. The features disclosed in the foregoing description and in the following examples may, both separately or in any combination thereof, be material for realising the invention in diverse forms thereof. 
       REFERENCES 
       [0045]    L. Vermeiren, F. Devlieghere, M. van Best, N de Kruijf, J. Debevere. 1999. Developments in the active packaging of foods. Trends in Food Science &amp; Technology 10: 77-86. 
         [0046]    L. Vermeiren, F. Heirlings, F. Devlieghere, J. Debevere. 2003. Oxygen, ethylene and other scavengers. In: R. Ahvenainen (Ed.) Novel Food Packaging Techniques. Woodhead Publishing, Cambridge, pp. 22-49. 
       EXAMPLES 
     Example 1 
       [0047]    The aim was to evaluate the effect of the microbial oxygen absorber on low-fat and high-fat cheeses. 
         [0048]    The microbial oxygen absorber  Lactococcus lactis  was obtained from Chr. Hansen (F-DVS DN-224, deposited under accession number DSM 11037). The following growth media containing lactose and protease peptone were produced: 
         [0049]    0.25% lactose: 
         [0050]    1.0 g peptone 
         [0051]    8.5 g NaCl 
         [0052]    2.5 g lactose 
         [0053]    1000 mL demineralized water 
         [0054]    0.50% lactose: 
         [0055]    1.0 g peptone 
         [0056]    8.5 g NaCl 
         [0057]    5.0 g lactose 
         [0058]    1000 mL demineralized water 
         [0059]    0.75% lactose: 
         [0060]    1.0 g peptone 
         [0061]    8.5 g NaCl 
         [0062]    7.5 g lactose 
         [0063]    1000 mL demineralized water 
         [0064]    The growth media were autoclaved, cooled to 30° C., and 100 g of F-DVS DN-224 was added. This gave a 10 8  cfu/mL concentration of bacteria. 
         [0065]    Two types of cheese were evaluated: A low-fat semi-hard cheese (5% fat in dry matter) and a high-fat semi-hard cheese (60% fat in dry matter). The products were sliced, and the surface sprayed with the bacteria slurry. The cheeses were subsequently packaged in a commercial packaging made of APET/PE and with a lid consisting of OPA/PE. A modified atmosphere containing 30-33% CO 2  and max 0.5% O 2 , and with N 2  as fill gas was used. The products were stored at 5° C. in the dark until time of sampling. 
         [0066]    The products were evaluated after 9, 11, 13 and 15 weeks for the low-fat cheese and after 15, 17, 19, and 21 weeks with respect to the high-fat cheese. The following evaluations were performed: Gas content (O 2  and CO 2 ) and sensory evaluations. Furthermore, pH, peptide mapping, and volatile aroma compounds were evaluated after 13 and 15 weeks for low-fat cheese and after 19 and 21 weeks with respect to high-fat cheese. 
         [0067]    The results are listed in Table 1. For clarity, only results after 13 and 15 weeks for low-fat cheeses and results after 19 and 21 weeks with respect to the high-fat cheese are listed. The entire test battery was applied at these times of withdrawal. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Effect of the use of a microbial oxygen absorber on physical, chemical, and 
               
               
                 sensory properties of semi-hard low-fat and high-fat cheeses. 
               
             
          
           
               
                   
                 Microbial 
                 Storage  
                   
                   
                   
                   
                   
                   
               
               
                   
                 O 2    
                 time 
                 O 2    
                 CO 2    
                   
                 Diacetyl 
                   
                   
               
               
                 Product 
                 absorber 
                 (weeks) 
                 (Note 1) 
                 (Note 1) 
                 pH 
                 “ppm” 
                 Peptide mapping 
                 Sensory evaluations 
               
               
                   
               
             
          
           
               
                 Low-fat 
                 − 
                 13 
                 0.021 
                 20.2 
                 5.60 
                 0.457 
                 Differences in peptide profiles of 
                 Flavor and odor were improved when 
               
               
                 cheese 
                 + 
                 13 
                 0.013 
                 20.3 
                 5.53 
                 0.625 
                 13 and 15 weeks cheeses are 
                 using the microbial O 2  absorber 
               
               
                   
                 − 
                 15 
                 0.019 
                 20.2 
                 5.53 
                 0.556 
                 noted 
                 Flavor end odor were improved when 
               
               
                   
                 + 
                 15 
                 0.005 
                 21.4 
                 5.53 
                 0.727 
                 No differences in peptide profiles 
                 using the microbial O 2  absorber 
               
               
                   
                   
                   
                   
                   
                   
                   
                 of products with end without 
                   
               
               
                   
                   
                   
                   
                   
                   
                   
                 microbial absorber were found 
                   
               
               
                 High-fat 
                 − 
                 19 
                 0.050 
                 17.2 
                 5.13 
                 1.039 
                 Difference in peptide profiles of 
                 Flavor was improved when using the 
               
               
                 cheese 
                 + 
                 19 
                 0.020 
                 20.7 
                 5.19 
                 0.945 
                 19 and 21 weeks cheeses were 
                 microbial O 2  absorber in combination 
               
               
                   
                   
                   
                   
                   
                   
                   
                 noted 
                 with high lactose concentrations. No 
               
               
                   
                   
                   
                   
                   
                   
                   
                 Slight differences in profiles of 
                 explicit differences in odor was noted 
               
               
                   
                 − 
                 21 
                 0.040 
                 19.1 
                 5.10 
                 0.674 
                 products with and without  
                 Odor was improved when using the 
               
               
                   
                 + 
                 21 
                 0.029 
                 19.0 
                 5.11 
                 0.952 
                 microbial absorber were noted 
                 microbial O 2  absorber. No pro- 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 nounced differences in flavor were 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 noted 
               
               
                   
               
               
                 Note 1: 
               
               
                 Only 0.75% lactose results. Same trend was noted for the two other lactose concentrations. 
               
             
          
         
       
     
         [0068]    No effect of the microbial oxygen absorber on pH was noted in either low-fat cheese or high-fat cheeses. The absorber may have a slight effect on the ripening of high-fat cheeses. Increased levels of diacetyl and acetoin (exemplified by diacetyl in Table 1) were noted in the cheeses. These compounds have a positive effect on the flavor of dairy products. Simple sensory evaluations revealed a positive effect of the microbial oxygen absorber. 
       Example 2 
       [0069]    The aim was to evaluate the effect of the microbial oxygen absorber at different residual oxygen levels. 
         [0070]    The microbial oxygen absorber  Lactococcus lactis  was obtained from Chr. Hansen (F-DVS DN-224). The following growth medium containing lactose and protease peptone was produced: 
         [0071]    3% lactose: 
         [0072]    1.0 g peptone 
         [0073]    8.5 g NaCl 
         [0074]    30 g lactose 
         [0075]    1000 mL demineralized water 
         [0076]    The growth medium was autoclaved, cooled to 20° C., and 10 g of F-DVS DN-224 was added. This gave a 47×10 7  cfu/mL concentration of bacteria. A reference containing only the peptone solution was used for comparison. 
         [0077]    40 mL 3% lactose/peptone water or peptone water with/without the microbial oxygen absorber were placed in a tray consisting of APET/PE and with a lid consisting of OPA/PE. Three packaging gas combinations were applied targeting at the following residual oxygen concentrations: 0.3%, 1%, and 21% (atmospheric air). CO 2  was constant at approx. 25% for the reduced oxygen gases and approx. 0% for the atmospheric air. N 2  was used as a fill gas. 
         [0078]    The packages were stored at 9° C. and 20° C. for 0, 7, 12, and 20 days. 
         [0079]    At time of sampling, gas content (O 2  and CO 2 ) and growth of  Lactococcus lactis  (M17 agar) were measured. Lactose content and pH were measured at the beginning and end of the experiment. Consecutive measurements were performed on the same package throughout the experiment. The results were averaged and based on triplicate determinations. The results of the oxygen measurements are listed in  FIGS. 2 and 3 . 
         [0080]    The microbial oxygen absorber reduced the oxygen level compared to a control without the microbial oxygen absorber. This effect was noted both at 9° C. and 20° C. 
       Example 3 
       [0081]    Product tests with the microbial oxygen absorber and Cheddar cheese have been performed. 
         [0082]    The aim was to evaluate the effect of the microbial oxygen absorber at different residual oxygen levels, and with and without inoculation  Penicillium camemberti.    
         [0083]    The microbial oxygen absorber  Lactococcus lactis  was obtained from Chr. Hansen (F-DVS DN-224). The following growth medium containing lactose and protease peptone was produced: 
         [0084]    3% lactose: 
         [0085]    1.0 g peptone 
         [0086]    8.5 g NaCl 
         [0087]    30 g lactose 
         [0088]    1000 mL demineralized water 
         [0089]    The growth medium was autoclaved, cooled to 20° C., and 0.5 g of F-DVS DN-224 was added. This gave a 27×10 6  cfu/mL concentration of bacteria. A reference containing only the lactose/peptone solution was used for comparison. 
         [0090]    The  Penicillium camemberti  strain was located at Kvibille Dairy and grown on DYES (dichloran yeast extract sucrose) agar. The spores were resuspended in sterilized water to obtain a 10 6  spores/mL solution. The  Penicillium camemberti  solution had a concentration of 12×10 5  spores/mL. 
         [0091]    40 mL 3% lactose/peptone water with/without the microbial oxygen absorber were placed in a tray consisting of APET/PE and with a lid consisting of OPA/PE. Cheddar chunks weighing approx. 100 g were dipped in paraffin and dried. The Cheddar was placed in the tray, and half of the samples were inoculated with 10 μl of the  Penicillium camemberti  suspension. 
         [0092]    Three packaging gas combinations were applied targeting at the following residual oxygen concentrations: 0.3%, 1%, and 21% (atmospheric air). CO 2  was constant at approx 25% for the reduced oxygen gases and approx. 0% for the atmospheric air. N 2  was used as a fill gas. 
         [0093]    The packages were stored at 9° C. and 20° C. for 0, 5, 10, and 20 days. 
         [0094]    At time of sampling, gas content (O 2  and CO 2 ) and growth of  Lactococcus lactis  (M17 agar) were measured. Lactose content and pH were measured at the beginning and end of the experiment. Consecutive measurements were performed on the same package throughout the experiment. The results were averaged and based on duplicate determinations. 
         [0095]    In samples only containing the microbial oxygen absorber, i.e. without the  Penicillium camemberti  inoculation, a clear effect of the presence of the absorber on the residual oxygen content was noted. When comparing the samples with both the microbial absorber and  Penicillium camemberti,  it appeared that the mold apparently used the oxygen present and that the oxygen levels were significantly reduced in the products containing both the microbial oxygen absorber and the  Penicillium camemberti  as compared to samples only containing the microbial oxygen absorber. 
       Example4 
       [0096]    The aim of the experiment is to evaluate the effect of the microbial absorber on quality changes caused by light exposure. 
         [0097]    Different residual oxygen levels are tested (between 0-5%). The cheeses are packaged in commercial packaging materials, the microbial oxygen absorber is sprayed on the cheese surfaces, and subsequently, the cheeses are packaged in modified atmospheres and stored at chilled temperatures in the dark or exposed to light (resembling retail exposure conditions). At time of withdrawal, gas content (O 2  and CO 2 ) is evaluated, and relevant physico-chemical, microbial, and sensory evaluations are carried out. 
       Example 5 
       [0098]    The aim of the experiment is to optimize the microbial oxygen absorber system. 
         [0099]    The following parameters are evaluated:
       Different growth substrates (milk, peptone water, milk hydrolysates and water)   Different growth temperatures (5° C., 9° C., and 20° C.)   Optimal concentration of microbial absorber material (inoculation percentage)   Method of application.       
 
       Example 6 
       [0104]    The aim of the experiment is to evaluate the optimal combination of microbial oxygen absorber concentration and residual oxygen content, which may subsequently result in increasing packaging machine speeds. The experiment involves spraying techniques and evaluations of different oxygen concentrations. (e.g. 0.1, 0.3, 1, and 5% O 2 ). Finally, up scaling experiments with different dairy products take place. Other food products are also included in the evaluations. 
       Example 7 
       [0105]    Delite 5% sliced cheese is placed in plastic trays and  Lactococcus lactis  subsp  lactis  DN224 in a lactose/peptone solution is sprayed onto the cheese. 
         [0106]    The plastic trays are packaged with a gas having the following composition: 0.4% O 2  og 43.5% CO 2 . 
         [0107]    The O 2  and CO 2  concentrations in the head space of the packaged cheese are measured after packaging as well as after the experiment. 
         [0108]    The following materials are used: 
         [0109]    Nr. Vium trays (GL440, 400 mu APET/4O mu PE) and lids (15 mu OPA/40 mu PE) 
         [0110]    Delite 5% sliced cheese from Nr. Vium dairy. 
         [0111]    Gas composition used for packaging: 43.5% carbon dioxide nd 04% oxygen. 
         [0112]    The lactose/peptione solution contains 
         [0000]    
       
         
               
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 NaCl 
                 8.5 
                 g 
               
               
                   
                 Peptone 
                 1.0 
                 g 
               
               
                   
                 Lactose 
                 30.0 
                 g 
               
               
                   
                 Water 
                 1 
                 Litre 
               
               
                   
                   
               
             
          
         
       
     
         [0113]    Autoclaved at 121° C. for 45 minutes 
         [0114]    The cheese is inoculated with the following amount of  Lactococcus lactic  DN-224:
       10 g frozen  Lc. lactis  culture is added per litre of lactose/peptone solution. Each cheese for packaging in a plastic tray is added 1 mL of the lactose/peptone by spraying.   The plastic trays are packaged (sealed) using a Multivac T200 from Multivac.   The packaged cheeses are incubated at 20° C. and at 9° C.       
 
         [0118]    The following packaged cheese products are prepared:
       1. 9 trays with cheese,  Lc. lactis  and lactose/peptone solution.   2. 9 trays with cheese and lactose/peptone solution   3. 9 trays with cheese and sterile water.   4. 9 trays with  Lc. Lactis  and lactose/peptone solution.   5. 9 trays with lactose/peptone solution.