Method for developing a red color in cured meat
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to a method for developing a uniform red color in cured meat, particularly fermented meats containing nitrate and/or nitrite. In particular, the present invention uses (a) a nitrate reducing bacteria, particularly Micrococcus, and (b) a Streptococcus lactis subspecies diacetylactis which acts in the presence of nitrite produced by a reduction of food grade nitrate to develop a cured red color. The Streptococcus lactis subspecies diacetylactis produces a red color in the meat at an early stage of the cure in the presence of nitrite without significant drop in pH (development of acid). The nitrite can be supplied by the nitrate reducing bacteria. Further development of the cured red color at a late stage of the cure is intensified by a reduction in pH by a lactic acid producing culture. 
     (2) Prior Art 
     The use of lactic acid producing Streptococcus lactis cultures to inhibit spoilage bacteria in ground meat is described by Reddy, S. G. et al in Journal of Food Science 35, 787-791 (1970). Streptococcus lactis subspecies diacetylactis strain is disclosed along with the suggestion that this subspecies generates an inhibitory substance which inhibits spoilage microorganisms. Ascorbic acid was added with the cultures of Streptococcus lactis to maintain the appearance of the ground meat which tended to oxidize to a brown color. The brown color is regarded by the consumer as an indication of a lack of freshness. When lactose was added to the cultures the inhibitory affect was increased, most likely because of the generation of lactic acid by the Streptococcus lactis from the lactose. Thus to a significant extent the inhibition achieved by Reddy et al are attributed to the lactic acid producing capabilities of the strains of Streptococcus lactis used. No edible nitrite was added to the meat and thus no cured red color was developed. 
     U.S. Pat. No. 3,814,817 to Everson et al describes the use of mixtures of lactic acid producing bacteria and Streptococcus diacetilactis in fermenting meat in the presence of food grade nitrite or nitrate. This patent suggests that it is desirable to maintain the natural cure color of the meat without any further discussion. U.S. Pat. No. 3,561,977 to Rothchild et al generally describes meat fermenting processes using lactic acid producing bacteria. 
     U.S. Pat. No. 4,477,471 to Gonzalez describes strains of Streptococcus lactis subspecies diacetylactis which lack the ability to produce lactic acid from lactose but which continue to generate an inhibitory substance effective against food spoilage microorganisms. The strains have been &#34;cured&#34; to rmove a 41 Mdal plasmid which encodes for lactic acid production from lactose while retaining the ability to produce the inhibitory substance. These strains are described as being useful in milk fermentations; however, there is no suggestion that they would be useful in curing meat. 
     The development of a cured red color in meat is very desirable. This prevents the dark brown color which the consumer regards as spoilage. U.S. Pat. No. 4,304,868 to Gryczka and Shah describe the use of Micrococcus varians, particularly NRRL-B-15,306, with lactic acid producing bacteria to develop a cured red color from nitrite and/or nitrate. Bacteria such as Micrococcus sp. NRRL-B-8048, as described in U.S. Pat. No. 4,013,797 to Gryczka are known to reduce nitrate or nitrite to develop the cured red color in meat. As far as is known, the use of Streptococcus lactis subspecies diacetilactis  with a nitrate reducing bacteria to develop a cured red color in meat is unknown. The reason is that Streptococcus lactis subspecies diacetylactis is not used commercially in meat fermentations and it is believed that the use of this species to develop an early red color in meat in the presence of a food grade nitrite is unknown. 
     OBJECTS 
     It is therefore an object of the present invention to provide a method for producing a cured red color in meat and also producing an inhibitory substance in the meat using an admixture of Streptococcus lactis subspecies diacetylactis and a nitrate reducing bacteria. In particular the present invention relates to a fermentation method which produces a cured red color in meat containing a food grade nitrite and/or nitrate. These and other objects will become increasingly apparent by reference to the following description. 
     GENERAL DESCRIPTION 
     The present invention relates to an improved method for curing meat by inoculating the meat with a bacteria which in the presence of a food grade preservative selected from nitrite, nitrate and mixtures thereof develops a cured red color in the meat which comprises inoculating the meat with a Streptococcus lactis subspecies diacetylactis and a nitrate reducing bacteria in the presence of an effective amount of the food grade preservative to develop the cured red color. 
     Further the present invention relates to an improved method for curing and fermenting meat by inoculating the meat containing a food grade preservative selected from nitrite, nitrate and mixtures thereof with lactic acid producing bacteria to reduce the pH of the meat which comprises inoculating the meat with a mixture of the lactic acid producing bacteria, a Streptococcus lactis subspecies diacetylactis and a nitrate reducing bacteria in the presence of an effective amount of the preservative so that the meat develops a cured red color while the meat is fermenting to reduce the pH. 
     The Streptococcus lactis subspecies diacetylactis develops an early red color in the meat without any pH reduction which is desirable from a processing point of view. The nitrate reducing bacteria develop a late red color particularly as the pH of the meat is reduced by fermentation. The reason for the early color development is uncertain; however, the presence of food grade nitrite is necessary. The nitrate reducing bacteria reduce any nitrate to a nitrite and the Streptococcus lactis subspecies diacetylactis act in the presence of the nitrite to develop the red color. The combination of those bacteria provides a reliable and desirable cured red color in the meat. 
     Various known strains of Streptococcus lactis subspecies diacetylactis can be used in the present invention, particularly ATCC 15346. Also the strains described in U.S. Pat. Nos. 4,172,899 and 4,191,782 to Vedamuthu can be used. 
     U.S. Pat. No. 4,477,471 to Gonzalez describes the various lactose negative (lac - ) strains of Streptococcus lactis subspecies diacetylactis (also known as Streptococcus diacetylactis) which are preferably used in the present invention. A lactose positive strain (lac + ) is used to produce the lactose negative (lac - ) strain by various means usually by the removal of a plasmid, although the trait can be encoded for by a gene on a chromosome and can be removed by curing techniques. The removal of a 41 Mdal plasmid from ATCC 15346 produces a preferred lac -  strain. The most preferred strain is lac -  cit -   strain Streptococcus lactis subspecies diacetylactis NRRL-B-15006. In this instance a 5.5 Mdal plasmid has been removed which encodes for citrate utilization. Also the nisin producing strains of Streptococcus lactis subspecies diacetylactis described in U.S. patent application Ser. No. 529,614 filed Sept. 6, 1983 can also be used in countries where nisin is allowed in foods. The preferred strains of Streptococcus lactis subspecies diacetylactis produce an inhibitory substance against gram negative bacteria (psychotrophs) which are food spoilage microorganisms. 
     In producing fermented meat products, Streptococcus lactis subspecies diacetylactis is mixed with a lactic acid producing bacteria conventionally used for meat fermentations and with a nitrate reducing bacteria. Lactic acid producing bacteria include for instance Lactobacillus plantarum as described in U.S. Pat. No. 3,814,817 to Everson, et al particularly NRRL-B-5461; Pediococcus pentosaceus particularly NRRL-B-11465 as described in U.S. Pat. Nos. 4,303,679 to Raccach, 4,452,895 to Gonzalez; and 4,508,738 to Gonzalez; Pediococcus cerevisiae, particularly NRRL-B-5677, as described in U.S. Pat. No. 3,561,977 to Rothchild and Olsen and; Lactobacillus casei NRRL-B-12344 as described in U.S. Pat. No. 4,407,828 to Raccach. Micrococcus varians NRRL-B-18051 (M-19) which is described hereinafter for nitrate reduction is freely available from the Northern Regional Research Laboratory in Peoria, Ill. upon request by name and access number. Other prior art nitrate reducing bacteria have already been described. 
     The Streptococcus lactis subspecies diacetilactis and lactic acid producing bacteria are preferably used in a cell count ratio of between about 10 to 1 and 1 to 10, respectively. The Streptococcus lactis subspecies diacetylactis and nitrate reducing bacteria are preferably used in a cell count ratio of between about 1 to 10 and 10 to 1, respectively. Any ratio which is effective to develop the cured red color in the meat can be used. The food grade nitrite or nitrate or mixtures thereof is preferably present in an amount between about 1 and 200 ppm. In the United States the maximum amount of food grade nitrite as sodium nitrate is 156 ppm. 
     The bacteria can be cultured to a level of about 1×10 8  cells per ml or higher and concentrated up to about 10 14  cells per ml. The cells can be preserved with a preservation agent and lyophilized or frozen. All of this is well known to those skilled sin the art. 
    
    
     SPECIFIC DESCRIPTION 
     Example 1 
     The meat formulation was for pepperoni and was as follows: 
     All pork (Boston Butt), comminuted, fat content 28-30%; 
     1.0% dextrose; 
     3.3% NaCl; 
     156 ppm NaNO 2  ; 
     0.003% BHA; 
     0.003% BHT; and 
     0.003% Citric Acid 
     where the percentages are by weight. 
     The cultures used were: 
     Streptococcus lactis subsp. diacetilactis NRRL-B-15006 
     Pediococcus pentosaceus NRRL-B-11465* 
    
     Micrococcus varians NRRL-B-18051 (M19) was used to reduce sodium nitrate (156 ppm) to nitrite so that Streptococcus lactis subspecies diacetylactis NRRL-B-15006 can develop a red color from the nitrite as shown in Table I. 
     
                       TABLE I                                                     
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Nitrate Cure                                                              
A. NRRL-B-18051 and NRRL-B-15006                                          
              15006 18051    15006 + 18051                                
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Sodium nitrate (156 ppm)                                                  
                1+      2+       4+                                       
Sodium nitrite (156 ppm)                                                  
                4+      2+       4+                                       
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 21 hr 24° C. no pH drop by 18051 or 15006                         
 Color Rating                                                             
 0  No color  Brown                                                       
 1+ Reddish Brown                                                         
 2+ Light red                                                             
 3+ Red                                                                   
 4+ Bright red cured color                                                
 
    
     It was concluded that Micrococcus varians NRRL-B-18051 did not produce very good color alone with either nitrate or nitrite. Streptococcus lactis subspecies diacetylactis did produce a good early color alone in the presence of nitrite and in the presence of nitrate when Micrococcus varians was present to reduce nitrate to nitrite. Streptococcus lactis subspecies diacetylactis did produce a good color alone. 
     In order to obtain a pH reduction, Pediococcus pentosaceus NRRL-B-11465 was used as shown in Table II. The cell count of the Pediococcus pentosaceus was about 4×10 7  cells per gram of meat. 
     
                       TABLE II                                                    
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B. Fermentation With Nitrate Alone                                        
NRRL-B-15006 and 18051 and NRRL-B-11465                                   
                   18051 +                                                
11465      18051   11465     18051 + 11465 + 15006                        
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Color 0         1.5+    2.5+   3+                                         
pH    4.81     5.41    4.85    4.71                                       
Time  24 hr    24 hr   24 hr   24 hr                                      
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 NaNO.sub.3 156 ppm                                                       
 Temp 73° F.                                                       
 0 hr pH = 6.10                                                           
 
    
     As can be seen from Example 1, Micrococcus varians NRRL-B-18051 reduces the sodium nitrate to nitrite so that NRRL-B-15006 can use it to develop color without a significant reduction in pH. In order to obtain a pH reduction Pediococcus pentosaceus NRRL-B-11465 or another lactic acid producing culture must be used. 
     A food grade citrate salt is conventionally used in meats to further accentuate the cured red color. Since the preferred Streptococcus lactis subspecies diacetylactis NRRL-B-15006 does not utilize citrate it is preferred for this further reason. Also, Streptococcus lactis subspecies diacetylactis NRRL-B-15006 does not metabolize lactose and will therefore not ferment the carbohydrate in milk solids which may be used as fillers in meat. 
     It is intended that the foregoing description only be illustrative of the present invention and that the invention be limited by the hereinafter appended claims.