Use of lanthionines for control of post-processing contamination in food

Abstract: Disclosed is a method for inhibiting the contamination of heat-processed food products by pathogenic or spoilage microorganisms which method involves treating the surface of the food product with a lanthionine bacteriocin.

Description: Background of the Invention Chung et al., 1989 App. Env. Microbiol. 55 : (6) 1329-1333 discuss the treatment of uncooked meats by soaking in a nisin solution and the effect of a nisin dip on raw meat inoculated previously with certain bacteria. They report a very short lifetime on nisin activity recovered from the raw meat (half-life of less than one day). M. Doyle in Food Technol. 1988 42 : (4) 169-171, describes the inhibitory effects of nisin on the growth and survival of L. monocytogenes . United States patent 4,597,972 discloses the mixing of food products with high levels of nisin to inhibit botulinum spore growth. European Patent Application, EP 0 384 319, discloses the use of antimicrobial composition comprising a Streptococcus-derived bacteriocin such as nisin, a Pediococcus-derived bacteriocin or a synthetic equivalent antibacterial agent in combination with a chelating agent(s). The composition may be used in conjunction with a foodstuff or with a food packaging film (with or without the chelating agent) to protect foodstuffs against growth of harmful bacteria such as Listeria. Summary of the Invention The present invention involves the application of a lanthionine bacteriocin to the surface of heat-processed foods such as cooked meats, fish, shrimp, lobster, shell fish and minimally processed meals in order to control post-processing contamination thereof. Description of the Invention The problem addressed by this invention is the surface contamination of heat-processed food products, especially meats, e.g. frankfurters, deli-meats (also referred to as cold cuts), cook-in-bag roast beef, chicken and cooked shrimp with undesirable bacteria, in particular Listeria monocytogenes. It has been discovered that L. monocytogenes on the surface of heat-processed foods such as frankfurters can be reduced or eliminated by applying a lanthionine bacteriocin such as nisin, subtilin, epidermin or Pep 5. to the surface thereof such as by dipping, spray coating or other surface application techniques. This surface application of such lanthionines results in a rapid reduction in L. monocytogenes cell numbers, and results in a continuation of such reduction for several weeks. Accordingly, it has been discovered that surface applications of nisin, subtilin, epidermin, Pep 5 or other lanthionine bacteriocin can be used after the heat treatment in the production of heat-processed meat products to control L. monocytogenes and other lanthionine bacteriocin sensitive food borne pathogens and spoilage organisms. Referring back to the Chung article which describes the dip treatment of raw meat, one is led to the conclusion that nisin is of limited utility in the treatment of uncooked meat products and even that utility which is exhibited has a short lifetime. The present invention calls for the surface application of one or more lanthionine bacteriocins to a heat processed meat product after the heating step. It has been discovered that the treatment of processed meats such as frankfurters in this manner results in a significant reduction in the levels of contamination L. monocytogenes within 30 minutes of such treatment and that the levels continue to decline for at least three weeks. This is in contrast to the published examples in which the effectiveness of nisin is of only a very short duration. Other heat-processed food products which are minimally processed such as fish, shrimp, shell fish and meats, poultry and meals which are cooked, for example poached, blanched or boiled, for sale chilled or for later serving chilled, would also benefit from surface treatment with a lantibiotic such as nisin after such processing. These foods are not retorted and the manner of sale and later use provides a surface exposed to post-processing contamination. The outgrowth of bacterial contamination may be inhibited or eliminated by the surface treatment disclosed herein. In addition, mixed foods such as salads for example pasta salads and meals containing such heat treated but minimally processed food products may also be surface treated. Surface treatment may be accomplished by dipping or spraying the food product with the lantibiotic solution. Nisin is particularly preferred and may be used in a surface treatment solution which contains from 0.1 to 1,000,000 units per mL, preferably from 500 to 200,000 units per mL. A preferred embodiment of the invention involves the surface treatment of a heat-processed food product with nisin in the absence of any significant amount of a chelating agent such as citric acid. The method of practicing the present invention is further illustrated by the following examples in which the nisin units were determined by the method of Tramer and Fowler reported in J. Sci. Fd. Agric., 1964 Vol. 15, 522-528. Example 1 Effect of Nisin on the Survival of L. monocytogenes on Frankfurters. An overnight culture [1% inoculum, grown at 35°C in BHI (brain heart infusion) medium from Difco] of L. monocytogenes Scott A was diluted 1:100 in 25 mM citrate buffer pH 6.0 (Buffer). A 1.5 mL portion of the diluted cells was transferred to 1.5 liters of Buffer in a sterile tub for inoculation the frankfurters which were dipped for 15 seconds in the inoculum, drained a few seconds, and dipped in triplicate into treatment solutions containing nisin at the indicated concentrations in 50 mL Buffer pH 6. At each condition, 6 frankfurters (two series of three each) were treated. The three frankfurters from a single treatment were vacuum packed in a sterile stomacher bag and stored for 30 minutes at room temperature. Packages were opened and each frankfurter was transferred to an individual stomacher bag. There was added 205 mL Modified Listeria Enrichment Medium (UVM) from BBL to the bag and the frankfurters were stomached for 2 minutes. The stomached material (10 mL) was transferred to each of 3 empty, sterile 20 x 150 mm tubes, 1 mL of this material was transferred to each of 3 tubes containing 9 mL UVM medium and to one tube containing 9 mL phosphate buffered saline (PBS) at pH 7.0. One mL of the 10 fold diluted material was transferred to each of 3 tubes containing 9 mL UVM medium and to one tube containing 9 mL PBS. One mL of the 100 fold diluted material was transferred to each of 3 tubes containing 9 mL UVM medium (i.e. a 3-tube most probable number procedure (MPN) was used with 10, 1, 0.1 and 0.01 mL stomached frankfurter in each set of tubes). The remainder of the sample was split into 4 volumes of about 70 mL each in sterile 25 x 200 mm tubes. All tubes were incubated at 35°C for 24 hours to enrich any L. monocytogenes . To detect L. monocytogenes , a 0.1 mL portion from each UVM tube was transferred to a tube containing 9 mL Fraser's broth and incubated 46 hours at 35°C. Positive tubes were detected by darkening of the medium, and viable cell number per frankfurter were determined from a 3-place MPN table. The results of this procedure are shown in Table 1. From the data of Table 1, it can be determined that a dip treatment with nisin followed by packaging and storage for 30 minutes of frankfurters inoculated with L. monocytogenes resulted in a decrease in the number of surviving cells and that this decrease is dependent on the concentration of nisin. Example 2 Effect of Nisin Against L. monocytogenes on Frankfurters Stored at 4°C for 21 Days. Frankfurters were treated as described above and the treated, vacuum packed franks stored for up to 21 days at 4°C. As shown in Table 2, the cell count of L. monocytogenes per frankfurter was greatly reduced and either continued to decrease (5,000 units/mL nisin) or remained extremely low (10,000 or 20,000 units/mL nisin) for at least 21 days. These data are in direct contrast to published reports on raw meat where dipping it in a solution containing 10,000 units per mL nisin produced no additional reduction in cell number after its immediate effect and where the outgrowth of L. monocytogenes began within 2 weeks.

Claims: A method of controlling the contamination of a heat-processed food by undesirable microorganisms which method involves treating the surface of a processed food with a lanthionine bacteriocin after the food product has been heat treated. The method of claim 1 in which the heat-processed food is a heat-processed meat product. The method of claim 2 in which the meat product is a frankfurter. The method of claim 2 in which the meat product is chosen from the group consisting of deli-meats and cook-in-bag roast beef, chicken and meals. The method of claim 1 in which the heat-processed food is a minimally processed food. The method of claim 5 in which the minimally processed food is chosen from the group consisting of shrimp, lobster and shell fish. The method of claim 1 in which the processed food is a salad containing such heat-processed food products. The method of claim 1 wherein the processed food is treated by dipping it into an solution of the lanthionine bacteriocin. The method of claim 8 wherein the solution contains from 0.1 to 1,000,000 units per mL. The method of claim 9 wherein the solution contains from 500 to 200,000 units per mL. The method of claim 1 wherein the lanthionine bacteriocin is nisin, subtilin, epidermin or Pep 5. The method of claim 1 wherein the lanthionine bacteriocin is nisin. A method of treating frankfurters which comprises contacting the surface of a heat treated frankfurter with an aqueous solution of a lanthionine bacteriocin to thereby render the frankfurter resistant to contamination by L . monocytogenes . The method of claim 12 wherein the lanthionine bacteriocin is nisin.

Inventors: COLLISON MARK W, FARVER TERRY F, HERALD PAULA J, MCDONALD CHRISTINE A, MONTICELLO DANIEL J, COLLISON, MARK W., FARVER, TERRY F., HERALD, PAULA J., MCDONALD, CHRISTINE A., MONTICELLO, DANIEL J.
Applicants: HAARMANN & REIMER CORP, HAARMANN & REIMER CORP.
Application year: 1991
Main classification: A23L3
IPC codes: A23B4, A23L3