Effect of Pork Belly-Type on the Microbiology of Bacon Cured with Or Without Potassium Sorbate

Effect of Pork Belly-Type on the Microbiology of Bacon Cured with or without Potassium Sorbate

M. K. WAGNERl, A. A. KRAFT2*, J. G. SEBRANEK3, R. E. RUST3, and C. M. AMUNDSON3

Departments ofFood Technology and Animal Science. Iowa State University, Ames, Iowa 50011

(Received for publication January 30, 1981) Downloaded from http://meridian.allenpress.com/jfp/article-pdf/45/1/29/1650545/0362-028x-45_1_29.pdf by guest on 02 October 2021

ABSTRACT becoming well supplied with reports concerning nitrite and alternative agents for cured meats. Current information suggests that sorbate is an Fat- and lean-grade hog bellies were used to evaluate the effective antibotulinal agent (13), but more information microbiology of bacon cured with either 40 ppm of nitrite is needed relative to other microorganisms. particularly +0.26% of potassium sorbate or 120 ppm of nitrite with no spoilage types on bacon. Further, little is known about potassium sorbate. Bacon slices were inoculated to provide an the relation of packaging and processing variables on 5 6 initial representative flora of 10 -10 organisms per g of meat. meat products cured with sorbate. Bacon was packaged in high barrier film with high vacuum The purpose of this study was to observe the effects of (28-29 in. of Hg), stored at 0 - 5 C, and analyzed at 0, 10,21 and 28 days after processing for enumeration and identification of different pork belly-types (fat or lean) on the bacterial mesophiJic, psychrotrophic and lipolytic organisms. In general, flora of vacuum-packaged bacon cured with or without the 40 ppm of nitrite + 0.26% of potassium sorbate cure potassium sorbate. provided greater bacterial inhibition (especially in fat bacon) than did the nitrite cure. Lactobacillus and Bacillus were the most common isolates characterized. MATERIALS Al'iD METHODS

In this study, an inoculum of representative bacon flora was used to insure sufficient numbers of organisms for treatment effects to be For centuries, nitrites and nitrates have been included observed. The bacon inoculum was derived from a mixed culture as curing salts used in the meat industry (2). In recent obtained by inoculating a loopful of growth from commercial bacon years, however, these additives have been characterized into 250 ml of tr}-pticase soy broth (BBL) and incubating it at 32 C for 24 h. One ml of growth from the broth culture was then pipetted over a as being highly carcinogenic to man (14). The possibility package of 14 bacon slices, to provide an initial population of 105-106 that nitrosamines, especially nitrosopyrrolidine formed organisms per g of experimental meat. Bacteria isolated from the by the nitrosation reaction in cooked bacon (4), may be a inoculum conformed to the genera Lactobacillus, Bacillus, Escherichia health hazard to humans has initiated the search for a (coW, Staphylococcus, Pseudomonas, Moraxella, Pediococcus, Leu successful nitrite substitute. conostoc and Microbacterium. Relative densities of each genus per ml inoculum were not calculated. Efforts are presently being made to reduce the level of Fat- and lean-grade hogs were obtained from a packing plant in nitrosamine formation, while maintaining the appear Central Iowa. Pork grades were assigned according to the packing ance, flavor and microbial safety of the cured product. plant's own standards, which correlated with backfat thickness. All One proposal by the USDA (19) had reduced maximum bacon was processed at the Iowa State University Meats Laboratory. levels of nitrite in bacon from 156 ppm to 120 ppm with Paired bellies (bellies from the same animal} were used to remove the specifications that levels be reduced further to 40 ppm influence of physiological and compositional differences. One belly from a pair served as the control and was pumped with 120 ppm of with the addition of 0.26 o/o of potassium sorb ate. sodium nitrite. The other belly was considered experimental and was In recent years, many investigations have been made pumped with 40 ppm of nitrite and 0.26% of potassium sorbate. Both on the nitrite-nitrosamine problem, and the literature is cures contained equal amounts of sodium erythorbate (550 ppm), salt (1.7o/o), sucrose (0.25%) and tripolyphosphate (0.2%). Bellies were brine-injected to 110% of their green weight. Smoking, chilling and slicing were identical for all bellies. A high barrier packaging film was 1Department ofFood Science and Nutrition, University of Minnesota, used with the product. Properties of the packaging film are shown in St. Paul, MN 55113. Table 1. A maximum obtainable vacuum (28-29 in. of Hg) was also 1Department of Food Technology. used with the product. After processing, bacon was stored at 0 -5 C and I Department ofAnimal Science. sampled at 0. 10. 21 and 28 days.

JOURNAL OF FOOD PROTECTION, VOL. 45, JANUARY 1982 30 WAGNER ET AL.

TABLE 1. Packaging film description \films provided by TABLE 3. Summary of tests used in the class(fication of Curwood, Inc., Green Wisconsin). isolates. Barrier film Contents Oxygen permeability Observations Techniques

High barrier 0.6 mil nylon, 75 75% 0.70 Gram stain - cell Hucker modification (18) saran & morphology 2.0 mil surlyn 38 90% 0.05 Metabolism of glucose Stab inoculation of OF medium and lactose (Difco) containing 1 o/o of glucose or Forty-g samples were aseptically removed from each pack on testing lactose in open and sealed tubes, days. Each sample was blended in a pint-size jar containing 360 ml of incubated for 2 weeks (10) 0.1% peptone-3% Tergitol solution (7) for 2 min, using an Osterizer Motility Needle inoculation of motility test blender (John Oster and Co., Milwaukee, Wisconsin) at a high speed medium (Difco) setting. Bacteriological Procedures employed for the enumeration of organisms are Cytochrome oxidase test Method described in presented in Table 2. Three replications were done and results were Analytical Manual using (1 o/osoln) subjected to an analysis of variance(} 7). N, N, N' ,N' -tetramethyl-p-phenylene Downloaded from http://meridian.allenpress.com/jfp/article-pdf/45/1/29/1650545/0362-028x-45_1_29.pdf by guest on 02 October 2021 TABLE 2. Bacteriological procedures employed. diamine•2HCl and a platinum loop (6) Types of Growth media Plating techniques Gelatinase formation Gelatin stab (I 8) microorganisms Gelatin streak plate Mesophiles Trypticasesoy agar Pour plates 30 C/24-36 h Lipase formation A modification of nile blue sulfate (BBL)a medium using 3 o/o pork fat (9) Psychrotrophs 5 C/14-18 days Tributyrin agar, streak plate Paper disc method (Bacto concentra Lipolytics Nile Blue Sulfate Poiir-p'la_,t-es~l~5--'en -14 days Sensitivity to penicillin medium (8) tion discs, Difco) Nitrate Nitrate broth (Difco) aBBL division ofBio Quest, Cockeysviile, Maryland. H2S production Stab and streak triple sugar iron agar slants (Difco). incubate at To determine effects of variables on tlora of the inoculated bacon, 30C and 37 C. random isolation of predominant colonies was done routinely. Typical Catalase production Addition of hydrogen peroxide to colonies from mesophilic, psychrotrophic and lipolytic plates were colony chosen as representative bacon tlora and were characterized in Growth at 5, 30,37 Trypticase soy agar (BBL), streak accordance with Table 3. Classification of isolates was derived from information found in Bergey's Manual of Determinative Bacteriology and45C plate (3). Halophilism Nutrient broth (Difco) with 6.5% NaCl, incubated at 37 C Coagulation of rabbit plasma RESULTS AND DISCUSSION Tube coagulase test (Difco), incubated at 37 C for 4 h Growth of aerobes has been shown to be slower on GrowthonKF KF Streptococcus agar (BBL) with vacuum-packaged meat than on meat packaged in air Streptococcus agar 1 o/o TTC, streak plate (1). Vacuum-packaging was effective in maintaining Citrate utilization Stab and streak slant of Simmons stationary or slightly declining levels of mesophilic Citrate agar (Difco), incubate for 48 h aerobic organisms regardless of whether sorbate was Lysine decarboxylase Inoculation of broth containing L-lysine (6) present in the cure or not, or if lean (Fig. 1) or fat (Fig. 2) Growth on Gardner's Streak plate (8) bacon was tested. Microbial analysis past day 28 was not medium done because these studies were intended to simulate the "shelf-life" span of commercial bacon. Previous work has shown nitrite to be more soluble in sed. The inhibitory effect of sorbate against psychro the lean portion of meat as opposed to the fat (20). Figure trophs on bacon is evidenced by these results and 1 shows a slight decline in numbers of bacteria on the substantiates other work indicating growth inhibition by nitrite-cured lean bacon, until day 21 where a slight sorbate of psychrotrophs from fish or beef (16). In the increase occurred. Some organisms are able to utilize present study with bacon. differences in bacterial sorbic acid as a substrate (15). Although differences in populations between lean and fat bacon were marked. counts over time were not pronounced, the nitrite Solubility differences of sorbate in fat and lean tissue sorbate cured lean bacon had an increase in numbers of may account for the antimicrobial effect of sorbate in organisms at day 21, indicating that sorbate may have bacon during storage. The type of bacon, whether fat or acted to stimulate growth. However, during continued lean, therefore is an important factor to be considered in storage to 28 days. numbers declined. Sorbate in effective use of sorbate in the cure. combination with nitrite may be expected to produce The influence of belly type on lipolytic organisms greater bacterial inhibition than nitrite alone during recovered from bacon cured with or without sorbate is prolonged storage of meat (12). shown in Fig. 4. As a general com paris ion, over the entire Figure 3 indicates that sorbate in the cure resulted in a storage period, fat bacon promoted greater growth of decrease in psychrotrophic organisms as time progres- lipolytic bacteria than did lean bacon. Also, in

JOURNAL OF FOOD PROTECTION, VOL. 45, JANUARY 1982 MICROBIOLOGY OF BACON 31

!22a NITRITE ll![] SORB ATE !!' Vl ::> ~ 4 z --- <( ---o-- '-' 0"' u !!' 5: ~ 5 0 Vl "'f- z 0 <( '-' I"' ~ 2 "'0 q u.. g; 0 0

z Downloaded from http://meridian.allenpress.com/jfp/article-pdf/45/1/29/1650545/0362-028x-45_1_29.pdf by guest on 02 October 2021 0 '-' z 0 ...J LEAN BACON o----o NITRITE o---0 SORBATE

10 21 28 0 10 21 28 FAT LEAN BELLY-TYPE AND STORAGE TIME (days) Figure 3. Psychrotrophic growth on fat and lean bacon after 0, 10, 21 and 28 days ofstorage at 0 to 5 C.

~NITRITE 10 15 20 25 30 DAYS OF STORAGE j:;::::;:;::d SORB ATE

Figure 1. Mesophilic growth from lean bacon after 0, 10, 21 and 28 days ofstorage at 0 to 5 C.

....______--~-:-::::::=-,-::::::------...---- ...... __ ....._ -.

z <( '-' "'0 u. 0

0z '-' 3 FAT BACON 3 e-NITRITE 0 10 21 28 0 10 21 28 ---· SORBATE FAT LEAN

BELLY-TYPE AND STORAGE TIME {days) Figure 4. Lipolytic growth on fat and lean bacon afterO, 10. 21 and 28 days ofstorage at 0 to 5 C. considering the entire storage period, the sorbate-nitrite cure was generally more inhibitory than the cure containing nitrite with no sorbate in both fat and lean 10 bacon. An analysis of variance of data for processing STORAGE TIME [days) variables (bacon type, cure, days in storage) is presented Figure 2. Mesophilic growth from fat bacon afterO, 10,21 and in Table 4. Of organisms tested, psychrotrophs were the 28 days ofstorage at 0 to 5 C. only group whose numbers were significantly different as

JOURNAL OF FOOD PROTECTION, VOL. 45, JANUARY 1982 32 WAGNER ET AL.

TABLE 4. Analysis ofvariance for processing variables. than with lean bacon bellies in restricting growth of Organisms Sourcea OF Sumof Mean F value PR>Fb psychrotrophic spoilage organisms. An additional paper squares square will be concerned with effects of packaging treatments Mesophiles Model 15 3.38 0.23 1.03 0.451 and cures on microbial spoilage. Error 32 6.98 0.22 Psychrotrophs Model 15 80.40 5.36 2.13 0.036 Error 32 80.55 2.52 ACKNOWLEDGMENTS CR 1 6.72 0.014 BL 1 7.16 0.012 Journal Paper No. J.JOJ61 of the iowa Agriculture and Home Lipolytics Model 15 51.81 3.45 0.97 0.507 Economics Experiment Station, Ames, Iowa. Project No. 2252. The authors thank Joan Andersen and Linda Halleland for typing the Error 32 114.13 3.57 manuscript. Appreciation is also expressed to Curwood, Inc. for partial DY 3 3.46 0.028 support of this work. Based on a paper presented at the 40th Annual a Abbreviations for source: DY =Day, CR Cure, and Meeting of the Institute of Food Technologists, New Orleans, La .. June BL = Belly-type. 8-ll, 1980. bPR>F values presented are ~0.05. Downloaded from http://meridian.allenpress.com/jfp/article-pdf/45/1/29/1650545/0362-028x-45_1_29.pdf by guest on 02 October 2021

REFERENCES a result of belly-type or curing ingredients used. Populations of psychrotrophs were significantly lower on 1. Baran. W. L.. A. A. Kraft, and H. W. Walker. 1970. Effects of fat bellies and bacon cured with sorbate than on lean carbon dioxide and vacuum packaging on color and bacterial bacon and bacon cured without sorbate. Organisms count of meat. J. Milk Food Techno!. 33:77-82. isolated most frequently were the gram-positive rods, 2. Binkerd, E. F., and 0. E. Kolari. 1975. The history and use of Lactobacillus and Bacillus, followed by the gram-nega nitrate and nitrite in the curing of meat. Food Cosmet. Toxicol. tive rods Moraxella and Escherichia coli (Table 5). Both 13:655-661. 3. Buchanan, R. E., and N. E. Gibbons (eds.). 1974. Bergey's manual cures (sorbate and nitrite with no sorbate) supported of determinative bacteriology. 8th ed. The Williams and Wilkens growth of similar types of organisms. Possibly the main Co .. Baltimore, MD. difference in characteristics of bacteria affected by belly 4. Fozio, T .. R. H. White, R. Dusold, and J. W. Howard. 1973. type was the greater numbers of lipolytic organisms on Nitrosopyrrolidine in cooked bacon. J. Assoc. Off. Anal. Chern. fat bellies than on lean bacon, but not necessarily 56:919-921. 5. Fiddler, W .. J. W. Pensabene, J. G. Fagan, and E. J. Thorne. pronounced differences in genera recovered. 1974. The role of Jean and adipose tissue on formation of From the information gained in this study, it may be nitrosopyrrolidine in fried bacon. J. Food Sci. 39:1070-1071. concluded that curing mixtures containing postassium 6. Food and Drug Administration. 1976. Bacteriological analytical sorbate and reduced nitrite levels (0.26% of sorbate and manual for foods, 4th eel. Food and Drug Administration, 40 ppm of nitrite) were as effective in inhibiting Washington, D.C. 7. Galton, M. M., J. R. Boring, and W. T. Martin. 1968. mesophilic bacterial growth on bacon as higher levels of Salmonellae in foods. Communic. Dis. Center, Public Health nitrite (120 ppm) with no sorbate. Further, the Service, U.S. Dept. of Health, Education and Welfare, Atlanta, Georgia. sorbate-nitrite cure was more effective with fat bellies con't. p. 37 TABLE 5. Number. type and percentage (of total no.) of isolates obtained by different screening methods (total no. of mesophilic isolates- 290; v.~••chl•at1·anhzcisolates- 70; 85). Types No. Mesophilic o/oof Psychrotrophic o/oof Lipolytic o/oof isolates total total total Gram + cocci Micrococcus 9 8 2.8 1 1.4 0 0 Streptococcus 34 32 11.0 0 0 2 2.3 Pediococcus 10 10 3.5 0 0 0 0 Leuconostoc 14 10 3.5 3 4.3 1.3 Staphylococcus 8 7 2.4 0 0 1 1.3

Gram+ rods Bacillus 88 64 22.1 6 8.6 18 21.2 Microbacterium 10 9 3.1 1 1.4 0 0 Lactobacillus 172 89 30.6 53 75.7 30 35.3

Gram- rods Moraxella 17 3 1.0 1 1.4 13 15.3 Pseudomonas 10 7 2.4 0 0 3 3.5 Salmonella 6 4 1.4 0 0 2 2.3 Escherichia coli 67 47 16.2 5 7.2 15 17.6

Total 290 70 85

JOURNAL OF FOOD PROTECTION, VOL. 45, JANUARY 1982 AEROMONAS AND YERSINIA FROM PORK 37

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