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A nitrite-free meat-curing system.

A Nitrite-free Meat-curing System

In North America alone some nine billion pounds of meat are cured annually using sodium nitrite. As a curing agent nitrite performs the following multiple functions:

1. It produces the cooked cured-meat pigment, dinitrosyl ferrohemochrome, which gives cured meat its characteristic pink colour.

2. It gives oxidative stability to meat by preventing lipid oxidation. This effect is complex, but it is believed to be responsible for producing the cured-meat flavour, and preventing the formation of the unpleasant warmed-over flavour which soon becomes apparent in cooked uncured meat on storage. Fat oxidation may also be involved in the differentiation of the flavour of meat from different species by the formation of a rich spectrum carbonyl compounds. However, nitrite is not unique in imparting oxidative stability to meat.

3. Nitrite has an antimicrobial effect which is particularly important in preventing the outgrowth of C. botulinum and the formation of a deadly toxin. However, here too nitrite is not unique.

Nitrite performs all of these functions very well, and has provided mankind with a variety of traditional and well-loved cured-meat products for many centuries. Unfortunately, it also has some serious disadvantages. In meat it forms carcinogenic nitrosamines, nitrosopyrrolidine and dimethylnitrosamine, in the part per billion range (Rubin, 1977). This is particularly true of bacon which reaches a high temperature on frying. On ingestion, nitrite may cause the formation of nitrosamines in the stomach (Wishnok, 1977). Yano et al. (1988) reported that at conditions that we might expect to find in the human stomach (37 [degrees]C and [sub.p]H3) extracts of broiled meats formed substantial levels of mutagens in the presence of nitrite, as measured by the number of revertants formed by S. typhimurium. Although we continue to use nitrite, it is the stated policy of the Canadian and U.S. governments to support the search for a substitute.

We have long recognized that the chance of finding a molecule which duplicates all of the functions of nitrite is infinitessimally small. We therefore decided to devise a multicomponent system for curing meat which, as a whole, would duplicate all the functions of nitrite - colour, oxidative stability and flavour, and preservative effect. In this work we have met with considerable success.

The Cured-meat Pigment

The pigment which gives meat its characteristic cured-meat colour is generally thought to be dinitrosyl ferrohemochrome (DNFH). It is formed from the meat pigment myoglobin, which consists of an iron porphyrin complex, the heme group, attached to the protein globin. In the presence of nitrite the bright red nitrosomyoglobin is formed, in which the H[sub.2]O in the axial position on the heme iron is replaced by nitric oxide, NO. The NO is formed from nitrite by the natural reducing activity of the muscle tissue, which is sometimes accelerated by the addition of reductants such as ascorbic acid. In heat-processed cured meat the globin has been split off to produce the final heat-stable pink pigment.

The structure of DNFH is shown in Figure 1. Lee and Cassens (1976) and Renerre and Rouge (1979) used [sup.15]N-labelled nitrite to independently confirm that the heated pigment contained twice as much [sup.15]N as the unheated pigment. Spectroscopic and theoretical considerations of Tarlagdis (1962) as well as work by Wayland and Olson (1974) lend further support to this interpretation of the structure of DNFH.

In our curing system we decided to preform the cured-meat pigment, and to use it to give meat the characteristic cured-meat colour.

Our basic material for preparing the cured-meat pigment is beef red blood cells, an abundant packinghouse by-product. The blood cells contain hemoglobin, which has the same heme group as myoglobin but differs in the protein portion of the molecule. The preparation of DNFH from hemoglobin involves two steps. The first is the preparation of hemin, an Fe[sup.3]+ porphyrin. Our own variation of the literature methods is described by Shahidi et al. (1984). The cured meat-pigment is produced from hemin using nitric oxide in the presence of a reducing agent (Shahidi et al., 1985). The yield starting with hemoglobin from beef red blood cells was 96%, and the purity was 95-99%.

The absorbance spectrum of the preformed pigment is shown as the top curve in Figure 2. The bottom curve is that of the pigment extracted from nitrite-cured ham. The two absorption maxima of both pigments are at 535 and 563 nm.

Unfortunately, the preformed pigment is unstable to light and air, as is the pigment in nitrite-cured meat. One approach to protecting the pigment prior to application is to use microencapsulation. A good encapsulating agent must be safe as a food additive, it must protect DNFH from oxidation during storage, and release it when required. Carbohydrate-based encapsulating agents have proven to be suitable in our application. In fact, our encapsulated DNFH can now be stored for one year or longer. We have used it successfully in preparing meat products, as will be illustrated later.

Oxidative Stability and Flavour

It has been previously mentioned that nitrite is an excellent antioxidant in meat systems, and that this is important in giving meat the characteristic cured flavour.

The classical technique for determining the extent of lipid oxidation in meat is the 2-thiobarbituric acid (TBA) test, which measures the amount of malondialdehyde formed. In this work we used the standard TBA test, as modified by Shahidi et al. (1987a). We have identified what may in fact be an alternative to the TBA test. Hexanal is the dominant breakdown product of lipid oxidation, and has been assigned a variety of odour characteristics, all unpleasant. Its effect on meat flavour must be substantial. We showed (Shahidi et al., 1987b) that the hexanal content (expressed as % of the hexanel content of the untreated control) and TBA numbers were closely correlated, and there was an indication that both correlated with sensory scores (see Table 1). Our work indicates that the hexanal content, after two days of storage, may be a more suitable indicator of lipid oxidation than the TBA test.

In comparing a number of antioxidants, we found that sodium ascorbate (SA) and sodium tripolyphosphate (STPP) are by themselves inadequate, but together they are highly synergistic giving a reasonably low TBA value (see Table 1). In the presence of a trace of a good phenolic antioxidant the TBA values are excellent, perhaps better than for nitrite. The samples were also evaluated organoleptically for flavour. The uncured control sample received a low sensory score. On the other hand, the sample containing SA, STPP and t-butylhydroquinone (TBHQ) was well accepted, and compared favourably with the nitrite-cured sample.

The Antimicrobial Effect

Nitrite acts as an important preservative in meat products and, as already mentioned, it impedes the outgrowth of C. botulinum. It plays an important role in making cured meats safe unless they are seriously abused. A nitrite-free curing system must duplicate this effect. Fortunately, nitrite is not unique in this regard. Many other agents have been suggested such as potassium sorbate, sodium hypophosphite, propyl paraben, and monomethyl and dimethyl fumarate. In a study at the University of Guelph (Wood et al., 1986) it was shown that each of these substances was an effective antimicrobial agent when used with our nitrite-free meat-curing system. Of these, sodium hypophosphite at 3000 mg/kg perhaps had a slight edge, and is the agent we used in the preparation of nitrite-free products. It is a crystalline salt which is bland in taste and readily soluble in pickle. It is an approved food additive in the United States.

Other alternatives have recently become available. Of these perhaps the most interesting is sodium lactate. The Oscar Mayer Foods Corporation received a patent for its use in meat products to delay the growth of C. botulinum (Anders et al., 1989). Its use in meat products as a flavour enhancer and as a preservative is now in the regulatory approval process in the United States. Sodium lactate is used at a rather high level, 2-3%. It seems to be reasonably effective, and it would certainly be an acceptable food additive.

Production of Wieners

The nitrite-free meat-curing system was tested on a pilot-plant scale for the production of wieners. This report briefly summarizes a large experiment reported in detail earlier (O'Boyle et al., 1990). The meat blocks were used: all-pork, pork with 10% beef, and all-chicken. The test runs were nitrite-free and contained the ingredients of the nitrite-free system - encapsulated DNFH at a level of 35 ppm of DNFH, 30 ppm TBHQ, and sodium hypophosphite at 0.3% of the batch weight. The control runs contained 200 ppm of sodium nitrite. The total weight of each batch was about four kilograms of which the meat constituted 66.7%. The rest was water, salt, binder, seasoning, sodium ascorbate and STPP. This is a fairly typical wiener formulation.

In producing the emulsion a Stephan vertical cutter/mixer with a vacuum attachment was used. The presence of air during the violent cutting and mixing action can cause complete oxidation of the pigment. The emulsions were stuffed out and processed conventionally in a pilot-scale smokehouse. Atomized liquid smoke (Griffith Imperial B) was applied.

The wieners had a fairly typical proximate analysis, although the fat content was somewhat low (about 10% for the chicken wieners and 15% for the others), and the protein somewhat high (15%).

In the evaluation of flavour by a panel of 15 tasters using triangle tests, significant differences were found after one and two weeks of storage. However, no significant flavour preference was ever perceived between the test and control wieners. All of the wieners were often described as being tough and rubbery, as might be expected at a high protein and low fat content, and in the presence of STPP. This tended to distract the panelists from focussing on flavour, as instructed. In fact, flavour-difference comments were highly inconsistent. A flavour-profile panel of six experienced tasters was asked to pinpoint the key flavour differences for the test and control wieners (all pork and pork with 10% beef). No specific flavour difference was found.

In judging internal colour, the Hunter reflectance spectrophotometer was used. The results showed that the nitrite-free wieners were somewhat darker and more red than the control wieners. It was to be expected that the wieners would be somewhat darker, since the DNFH was added to a background colour that was light-brown. The redness can be readily controlled by adjusting the DNFH level. The experimental pork/10% beef wieners were somewhat darker and more red than their all-pork counterparts. This was due to the fact that beef is very rich in myoglobin, and also somewhat more DNFH (45 ppm instead of 35 ppm) was used in this case. It is felt that more beef can in fact be tolerated. The colour readings remained unchanged during the six-week duration of the test.

Visual evidence of the colour quality is presented for nitrite-free chicken wieners on the front cover of the magazine. The photograph on the front cover of the magazine shows that the nitrite-free wieners (top) compare very favourably to the control. They are virtually indistinguishable as far as colour is concerned.

The microbial quality of the wieners was evaluated over a six-week period by total plate counts. There was very light growth for the first four weeks. However there was an unexpected spurt in growth by the end of the sixth week. There was no difference between the test and control wieners. In commercializing the process more microbiological work will have to be done, both in scope and depth.

The oxidative stability of the wieners was followed by the TBA test. It is interesting to note that lipid oxidation was almost completely prevented by the nitrite-free curing system, both when stored in air and vacuum packaged.

Firmness of the wieners was determined by the method of Voisey et al. (1975). All samples were substantially stiffer than normal wieners for reasons already given. The one control batch that did not contain STPP was significantly less firm than the others. In the rest of the tests, there was essentially no difference between the test and control wieners. There is good reason to believe that texture can be controlled by changes in the formulation.


The nitrite-free curing system can produce wieners which essentially cannot be distinguished from their nitrite-cured controls. The process has been extended to the curing of solid meat cuts such as ham. It is felt that the nitrite-free meat-curing system has the potential to supply the consumer who is concerned about nitrite with a viable alternative.


Anders, R.J., Cerveny, J.G. and Milkowski, A.L. 1989. Method for delaying Clostridium botulinum growth in fish and poultry. U.S. Patent 4,798,729. Lee, S.H. and Cassens, R.G. 1976. J. Food Sci. 41: 969. O'Boyle, A.R., Rubin, L.J., Diosady, L.L., Aladin-Kassam, N., Comer, F., and Brightwell, W. Food Technology 1990, 44: 88. Renerre, M. and Rouge P. 1979. Ann. Tecnol. Agric. 28: 423. Rubin, L.J. 1977. Can. Inst. of Food Sci. Technol. J. 10(1): A11. Shahidi, F., Rubin, L.J., Diosady, L.L., Chew, V., and Wood, D.F. 1984. Can. Inst. of Food Sci. Technol. J. 17: 33: Shahidi, F., Rubin, L.J., Diosady, L.L., and Wood, D.F. 1985. J. Food Sci. 50: 272. Shahidi, F., Rubin, L.J. and Wood, D.F. 1987 a.J. Food Sci. 52: 564. Shahidi, F., Yun, J. Rubin, L.J. and Wood, D.F. 1987b. Can. Inst. of Food Sci. Technol. J. 20: 104 Tarlagdis, B.G., 1962. J. Sci. Food Agric. 13: 481. Voisey, P.W., Randall, C.J., and Larmond, E. 1975. Can. Inst. of Food Sci. Technol. J.8:23. Wayland, B.B. and Olson, L.W. 1974. J. Am. Chem. Soc. 96:19. Wishnok, J.S. 1977. J. Chem. Educ. 54: 440. Wood, D.F., Collins-Thompson, D.L., Usborne, W.R. and Picard, B. 1986. J. Food Protection. 49: 691. Yano, M., Wakabayashi, K., Tahira, T., Arakawa, N., Nagao, M., and Sugimura, T. 1988. Mutation Research 202: 119.

Table : Hexanal Content, TBA Numbers, and Sensory Scores of Meat Systems (1) (Shahidi et al. 1987b) (1) The cooked meats were stored at 4 [degrees] C. The additives were sodium ascorbate, SA sodium tripolyphosphate, STPP; butylated hydroxyanisole, BHA; and t-butylhydroquinone, TBHQ.

PHOTO : Figure 1 Shematic representation of the cooked cured-meat pigment dinitrosyl ferrohemochrome.

PHOTO : Figure 2 Absorption pattern of DNFH pigment in 80% acetone-water
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Author:Rubin, Leon J.; Diosady, Levente L.; O'Boyle, Adam R.
Publication:Canadian Chemical News
Date:Jul 1, 1990
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