Low-acid, high-moisture processed cheese spread and method of making

High-moisture, high-pH, shelf-stable cheese spreads containing cheese, preferably a cheese having a pH of 5.4 or lower such as Swiss, Cheddar, American, mozarella, skim milk cheese, or cheese mixtures, water sufficient to provide a total moisture of from 51 to 58% and a pH of from 5.3 to 6.0 are preserved by adding sodium chloride, a phosphate salt, sodium citrate, and sodium lactate in sufficient amounts to maintain the composition free from the growth of Clostridium botulinum and the production of toxin by those organisms during room temperature storage for a period of at least 180 days, preferably 300 days. Some embodiments contain about 1 to 2% sodium citrate, about 1 to 2% sodium lactate, and a combined level of dibasic sodium phosphate and sodium chloride ranging between about 1.3 and 2.2%, and have a moisture content of 52 to 55%, and an overall pH of about 5.3 to 5.6.

TECHNICAL FIELD 
The invention relates to a method for preparing an improved cheese spread 
of the low-acid, high-moisture type, and especially to one with an 
improved preservation system which enables the use of higher pH values 
and/or moistures than currently available in commercial products without 
rendering them susceptible to the production of toxins by microorganisms 
such as Clostridium botulinum. 
Cheese spreads pose problems in preservation in addition to those of foods 
such as meat and vegetables. Unlike those other products, which can be 
heat processed if their pH and moistures are not low enough (e.g., pH&lt;4.5 
and a.sub.w &lt;0.85) to assure safety by simply aseptic packaging, cheese 
spreads will separate and lose other textural and flavor attributes if 
heated in the manner of other foods. Accordingly, it has been necessary to 
utilize moisture contents of about 52% or less, along with a number of 
other preservatives including salt, phosphate salts, and acids. 
Because of these limitations, it has not been possible to utilize more 
moisture for, as a primary example, reduced-fat, shelf-stable cheese 
spreads. 
There is a present need for a preservation system for use with processed 
cheese spreads which will enable the use of higher pH values and/or higher 
moistures. 
BACKGROUND ART 
The art of making and preserving processed cheese spreads for room 
temperature storage in hermetically-sealed containers has developed 
greatly in the past two decades, but there yet seem to be certain barriers 
in terms of moisture and pH which cannot be circumvented. 
In the Journal of Food Protection, 1979, 42 (10) 784-786, D. A. Kautter, et 
al., reported that five non-refrigerated, pasteurized processed cheese 
spreads, considered shelf-stable, were studied for their ability to 
support growth and toxin production by spores of Clostridium botulinum, 
types A and B. On the basis of pH and water activity (a.sub.w), Cheese 
with Bacon, Limburger, Cheez Whiz.RTM., Old English, and Roka Blue cheese 
spreads were selected for the study. Sample pH ranged from 5.05 to 6.32 
and a.sub.w from 0.930 to 0.953. Fifty jars of each cheese spread were 
inoculated with 24,000 spores each, and an additional 50 jars of the 
Cheese with Bacon spread received 460 spores each. The inoculum consisted 
of five type A and five type B strains in 0.1 ml of 0.85% NaCl. At 
35.degree. C., 46 jars of Limburger spread and 48 jars of the Cheese with 
Bacon spread which received the greater inoculum became toxic starting at 
83 and 50 days, respectively. One jar of Cheese with Bacon spread which 
received 460 spores became toxic. The average toxicity of the Limburger 
was 3000 mouse LD/ml of extract as compared with 54 mouse LD/ml for the 
Cheese with Bacon spread. Results of this study were considered in 
determining whether these cheese spread products should be treated as 
low-acid canned foods under the Good Manufacturing Practice Regulation of 
the FDA. See also, D. A. Kautter, et al., Abstracts of the Annual Meeting 
of the American Society for Microbiology, 1978, 78, 192. 
N. Tanaka, et al., in the Journal of Food Protection, 1979, 42 (10) 
787-789, reported on a study wherein pasteurized processed cheese spread 
with pimentos, packaged in glass jars, inoculated during processing with 
1000 spores per gram, developed neither gas nor toxin at 52 or 54% 
moisture when sodium phosphate was used as the emulsifier. When, however, 
sodium citrate was the emulsifier, the product developed gas at 52% 
moisture and became toxic at 54%. At 58% moisture, the product became 
gassy and toxic with either emulsifier. It was concluded that since the 
product is commercially manufactured at 52% moisture with phosphate 
emulsifier, a substantial margin of safety existed. 
In a later paper, Tanaka, et al., reported that sodium chloride and 
disodium phosphate inhibited butulinal toxin production with similar 
effectiveness in tests of a series of process cheese spreads having 
various levels of sodium chloride, disodium phosphate, moisture and pH 
that were challenged with Clostridium botulinum types A and B and 
typically incubated at 30.degree. C. for 42 weeks (Journal of Food 
Protection, 1986, 49 (7) 526-531). The addition of 0.25% lactic acid 
helped inhibit toxin formation, but the observed inhibition was largely 
attributed to the reduction of pH. The investigators concluded from the 
study that no single factor is responsible for the safety of unsterilized 
pasteurized process cheese spreads, but safer products had lower moisture, 
higher NaCl and phosphate concentrations, and lower pH's. 
In U.S. Pat. No. 4,346,117, Thompson, et al., disclosed processing corned 
beef and smoked poultry, to make them more resistant to the outgrowth of 
Clostridium botulinum and the formation of enterotoxins during storage. 
The products contained less than 120 ppm of alkali metal nitrite salt and 
an effective amount of hypophosphorous acid or one of its water soluble 
non-toxic salts. Satisfactory preservation of meat was said to be achieved 
with reduced amounts of nitrite. In a related application (Eur. Pat. Ap. 
Pub. No. 66170), botulinal toxin inhibition in reduced-sodium processed 
American cheese foods and spreads (and high carbohydrate food products 
having a ratio of carbohydrate and protein to fat greater than 1) was 
reported by adding 1000-3000 ppm of hypophosphorous acid or its non-toxic 
water-soluble salts and, optionally, up to 52 ppm of sodium nitrite. 
Similarly, in the Journal of Food Protection, 1985, 48 (1) 63-69, C. 
Karahadian, et al, described tests on moderately-reduced (about 55%) and 
highly-reduced sodium (about 75%) processed cheese foods and spreads 
prepared from Cheddar cheese. The plastic, but pourable processed cheese 
samples were incubated at 62.degree. C. with 1 or 1000 spores/g of a mixed 
strain Clostridium botulinum spore suspension, held at 4.4.degree. C. for 
24 hours, then at 30.degree. C. for 84 days. With an inoculum of 1000 
spores/g, botulinal toxin was not detected in moderately-reduced sodium 
cheese foods and spreads (pH 5.15-5.26) containing .delta.-gluconolactone. 
With highly-reduced sodium spreads and foods, the presence or absence of 
toxin was not always predictable, although .delta.-gluconolactone played 
an important role in delaying toxinogenesis. When five emulsifiers were 
used individually at 2.5% in screening tests, samples emulsified with 
disodium phosphate and, possibly, trisodium citrate showed some inhibition 
of toxin formation; the three potassium emulsifiers tested were 
ineffective in inhibiting toxin formation. 
M. R. Maas, et al., reported delays in toxin production by Clostridium 
botulinum in cook-in-bag turkey products containing 1.4% sodium chloride, 
0.3% sodium phosphate, and 0 to 3.5% sodium lactate (Applied and 
Environmental Microbiology, 1989, 55, 2226-2229). Though the products were 
cooked by immersion in heated water prior to incubation at 27.degree. C. 
for up to 10 days, processed turkey containing 0, 2.0, 2.5, 3.0, or 3.5% 
sodium lactate was toxic after 3, 4 to 5, 4 to 6, 7, or 7 to 8 days, 
respectively. 
In addition to the more traditional preservatives, the antibotulinal 
effectiveness of nisin in pasteurized process cheese spreads has been 
investigated. In the United States, nisin is generally recognized as safe 
for use in some pasteurized cheese spreads to prevent both spore outgrowth 
and toxin production by Clostridium botulinum. In other countries, nisin 
has been used for a number of applications, including extension of the 
shelf life of dairy products and prevention of spoilage of canned foods by 
thermophiles. E. B. Somers and S. L. Taylor reported in the Journal of 
Food Protection, 1987, 50 (10) 842-848, on work with pasteurized processed 
cheese spreads having moisture levels of 52-57% with 0-2.0% added NaCl, 
disodium phosphate levels of 1.4-2.5% and nisin levels of 0-250 ppm that 
were inoculated with about 1000 spores/g (except in one experiments 
wherein the spore levels were varied between 10 and 1000 spores/g). The 
products were incubated at 30.degree. C. for up to 48 weeks. Nisin was an 
effective antibotulinal agent. Addition of nisin allowed formulation of 
the processed cheese spread with reduced sodium levels (e.g., addition of 
1.4% disodium phosphate and no NaCl) or slightly higher moisture levels 
(55-57%) compared with typical commerical pasteurized process cheese 
spread. Higher levels of nisin (100 and 250 ppm) were required to prevent 
outgrowth of botulinal spores in the highest moisture or most reduced 
sodium samples. In a sample having 52% moisture, prepared with 2.5% 
disodium phosphate and no added NaCl, 12.5 ppm nisin completely prevented 
outgrowth and toxin production by C. botulinum. See also GB Patent 
2,141,016 A to Taylor, which suggested adding 2,000 to 10,000 I.U. nisin 
per gram of cheese. 
In a related U.S. patent (U.S. Pat. No. 4,584,199), S. L. Taylor described 
a process for inhibiting outgrowth of Clostridium botulinum spores and 
subsequent toxin formation in high-moisture, pasteurized processed cheese 
spreads. The cheese was a blend of American cheese, dried skim milk and 
whey solids. Test batches were produced containing 58% moisture, 1.45% 
Na.sub.2 HPO4 and 1.2% NaCl, with or without nisin at levels of 12.5, 100 
or 250 ppm At the high level, nisin completely prevented outgrowth and 
toxin production by C. botulinum. At 100 ppm, nisin severely limited 
outgrowth and toxin production, but 12.5 ppm was ineffective. 
In U.S. Pat. No. 4,597,972, S. L. Taylor discloses a process for 
controlling the growth of Clostridium botulinum spores and production of 
botulinum toxin in a food products comprises adding nisin or a 
nisin-producing culture to the food. The disclosure concerned foods other 
than high moisture content pasteurized process cheese products, such as 
tomato, meat, fish, poultry products. The nisin may be used together with 
other agents, e.g. nitrite or sorbate.

DISCLOSURE OF THE INVENTION 
It is an object of the invention to provide a method for preparing a 
low-acid, shelf-stable, processed cheese spreads with improved ability to 
resist the production of toxins by spores of Clostridium botulinum. 
It is another object of the invention to provide low-acid, shelf-stable, 
processed cheese spreads which have moisture contents above those 
available in current commercial products. 
It is another object of the invention to provide shelf-stable, processed 
cheese spreads having milder, less-acid flavors than those currently 
available. 
These and other objects are realized by the present invention which 
provides a method for preserving a high-moisture, high-pH, shelf-stable 
spread composition containing cheese by adding to the formulation a 
preservation system containing sodium chloride, a phosphate salt, sodium 
citrate, and sodium lactate in sufficient amounts to maintain the 
composition free from the growth of Clostridium botulinum and the 
production of toxin by those organisms during room temperature storage for 
a period of at least 180 days, and adjusting the water content so that the 
total moisture in the final composition ranges from about 51% to about 58% 
and adjusting the pH from about 5.3 to about 6.0. 
In some embodiments, shelf-stable cheese spread formulations of the 
invention have a moisture content of 52 to 55%, contain 1 to 2% sodium 
citrate, about 1 to 2% sodium lactate, and a combined level of dibasic 
sodium phosphate and sodium chloride ranging between about 1.3 and 2.2%, 
and exhibit an overall pH of about 5.4 to 5.8. 
INDUSTRIAL APPLICABILITY 
This invention is based upon the finding that a preservation system 
comprising phosphate, lactate, citrate, and salt can be used to prepare 
shelf-stable, high-moisture, low-acid cheese spread compositions. 
The invention will be described below with specific reference to a 
preferred embodiment wherein a cheese spread having a moisture content of 
52 to 56% and a pH of from 5.4 to 5.8 is produced which is stable against 
the production of toxins from spores of Clostridium botulinum when stored 
in moisture-impermeable packaging at room temperature for a period of at 
least 180 days, and preferably at least 300 days. The term "room 
temperature" is defined to mean a temperature within the range of from 
20.degree. to 25.degree. C. The typical moisture-impermeable packaging 
consists of glass jars with snap-on metal lids, but can be of any suitable 
material including plastic tubes or tubs, as well as pressurized metal 
cans with dispensers. Preservation is achieved without the addition of 
nisin. 
The type of cheese will affect the ability of the processed cheese spread 
to resist the production of toxins from the spores of Clostridium 
botulinum. This is principally due to the pH and the salt levels. For 
example, it is preferred to start with cheeses having a pH of no higher 
than about 5.4, preferably about 5.2, and a salt (sodium chloride) level 
of from about 1 to about 2%. This percentage and those used throughout 
this description are by weight and based on the weight of the formulation 
at the indicated stage of processing. Among the types of cheese preferred 
are Cheddar, Swiss, American, reduced-fat cheeses, part-skim mozzarella, 
skim milk cheeses, and mixtures thereof. Where the pH and salt levels do 
not meet the above target levels, it is desired to adjust the amounts of 
added acid or salt to meet these targets. Likewise, where the cheese 
contains salt, added levels added can be correspondingly, as in the case 
of Cheddar cheese, which typically contains 1.4 to 1.5% salt. 
The processed cheese spreads made according to the method of the invention 
will also contain an emulsifier of a type typically employed to maintain 
the desired smooth texture through processing and storage. The use of 
dibasic sodium phosphate (Na.sub.2 HPO4.2H.sub.2 O) is preferred at a 
level of at least 0.6% at a level to give a combined level of this 
compound and sodium chloride of from 1.3 to 2.2%. Sodium citrate can be 
employed as an adjunct emulsifier and still obtain the desired degree of 
stability. 
At pH values of up to 5.8, 1.5% of the phosphate emulsifier is effective in 
preventing the production of toxins by spores of Clostridium botulinum 
when employed with sodium chloride at the indicated level and sodium 
citrate (as the dihydrate) as an adjunct emulsifier at a sufficient level. 
It is contemplated to employ the sodium citrate at a level of from about 
1.0 to about 2.0%, testing in the examples being done at 1.23%. It has 
also been determined that samples unstable at 0.6% phosphate can be 
increased in stability to prevent the production of the noted toxins by 
the addition of sodium lactate, e.g., at a level of about 1.0 to 2.0%, 
1.3% being specifically tested. 
The pH of the preferred products is within the range of from 5.2 to 5.8, 
with the exact level being selected, not only for preservation, but also 
to achieve the desired flavor in the product. It is an advantage of the 
method of the invention that the pH can be above 5.4 without rendering the 
formulation susceptible to the production of the noted toxins. This is of 
particular advantage when it is desired to produce cheeses such as 
reduced-fat processed cheeses (e.g., similar to cream cheese) and the like 
which have relatively mild, or at least non-acid flavors and, in some 
cases, require higher pH values to be suitably spreadable. 
The cheese spreads are made as known to the art other than for the use of 
the newly-discovered effective preservation system and the method for its 
use. In this regard, the procedure of Example 1 is effective as are those 
of the above-noted references. Typically, the procedure will entail mixing 
liquid ingredients such as cream, water, milk, and the like, with soluble 
solids such as salt, emulsification agents such as the phosphates or 
citrates, colorants, flavorants, spices, any sugars or dextrins, gums or 
other thickeners, and possibly antimycotics such as potassium sorbate or 
the like. The resulting mixture is blended and heated while the cheese is 
added, preferably in grated form with the aid of a scraped-surface mixing 
kettle. The ingredients are agitated until the mixture is smooth and any 
solid inclusions such as pimentos, bacon, or the like, are added in known 
fashion. 
Following mixing of the ingredients, the cheese mixture is heated to a 
processing temperature of about 190.degree. F. and the ingredients blended 
until smooth. For flavor enhancement, the temperature is typically held at 
the processing temperature for at least a minute or two prior to filling 
and cooling. Specific instructions for the preparation of cheese spreads 
according to the invention are given in greater detail in the examples 
that follow. 
An advantage of the invention is that a shelf-stable cheese spread product 
exhibiting high moisture and high pH can be made by the simple process of 
judicious selection of added salts in the preservation system. Cheese 
spread compositions made according to the method of the invention exhibit 
good organoleptic characteristics as well as freedom from toxin production 
after storage, with the range of cheeses expanded over prior art products. 
The following examples are presented to further explain and illustrate the 
invention and are not to be taken as limiting in any regard. Unless 
otherwise indicated, all parts and percentages are given based on the 
weight of the composition at the indicated stage of processing. 
EXAMPLE 1 
A cheese spread was prepared by mincing about 65 to 65.5% Cheddar cheese 
and processing in a "silent cutter" until a contiguous paste was formed. 
Sorbic acid (about 0.09-0.11%), carageenan (about 0.07-0.08%), and yeast 
extract (about 0.35-0.4%) were sprinkled into the mass, then water (about 
7-8%) and heavy cream (about 13-14%) were added, followed by lactic acid 
(about 0.85-0.9%), NFDM (about 6.8-6.9%), and whey (about 5-5.5%), and the 
mixture was blended together until homogeneous. The temperature of the 
blend following processing in the silent cutter was 76.degree. F.; 
temperatures remained in the high 70's during processing and filling, 
after which the product was immediately transferred to a 
38.degree.-42.degree. F. cooler. The prepared cheese base had a pH of 4.9 
and a moisture content of 39.8%. 
The pasteurized process cheese spread base prepared as above was 
transported frozen in three-pound blocks. The cheese was stored at 
-20.degree. C. then thawed at 4.degree. C. before usage. Batches (1500 g 
final weight after addition of moisture) were prepared by heating ca. 1360 
g cheese base in a steam-jacketed cheese cooker until slightly melted and 
easily mixed. About one third of the moisture was added as water, followed 
by the addition of the sodium chloride, sodium phosphate and sodium 
citrate and blended without steam until the mixture was homogeneous. When 
the mixture was smooth, an additional one third of water volume and the 
appropriate amount of 6N HCL or 5M NaOH was added to adjust the pH. The 
product exhibited no processing problems, and control product incubated in 
the absence of Clostridium botulinum as set out below exhibited good 
viscosity, taste and mouthfeel. 
Product was heated with agitation to 88.degree. C. (190.degree. F.) and 
held for 2 min before a 10-strain mixture of Clostridium botulinum spores 
(5 type A and 5 type B, all proteolytic) was added at a rate of ca. 1000 
spores/g. The sauce was held at 88.degree. C. for an additional 1 min, 
then quickly poured into sterile 20 ml glass vials (29.times.60 mm, 
Wharton 225288) and capped. All samples were stored under anaerobic 
conditions (gas mixture of 80% CO.sub.2, 10% H.sub.2 and 10% N.sub.2 in a 
BBL anaerobe jar) at 30.degree. C. (abuse conditions) and assayed (5 per 
sampling time) at 0, 4, 8, 12, 16, 24, 32, 40 and 48 weeks postinoculation 
for pH and botulinal toxin using the mouse bioassay (FDA Bacteriological 
Analytical Manual). Testing of a trial was discontinued when botulinal 
toxin was detected in at least one sample for two sampling times. 
Moisture, pH and C. botulinum spore levels were determined in triplicate 
at 0-time and at the end of incubation at 48 weeks. Analyses for sodium 
chloride, citrate and phosphate were done in duplicate at 0-time. Methods 
used for these determinations included: 
______________________________________ 
1. direct pH Orion 816 combination pH probe, 
Corning 140 pH meter 
2. aerobic plate count 
FDS Bacteriological Manual, 6th ed. 
3. moisture AOAC 926.08, 15th ed. 
4. sodium chloride 
AOAC 935.43, 15th ed. 
5. phosphate atomic absorptin for phosphorus content by 
outside contract laboratory; additional 
samples sent to Nabisco for analysis 
6. citrate AOAC 976.15, 15 ed; 
colorimetric method 
7. lactate analysis by center for Dairy Research, 
University of Wisconsin-Madison 
8. sorbate analysis by outside contract laboratory 
9. C. botulinum spores 
Most Probable Number (MPN) method 
FDA Bacteriological Manual, 6th ed. 
______________________________________ 
Preliminary experiments summarized in FIGS. 1 to 4 were run to determine 
the relationship of salt levels and pH in the test results. The graphs 
show the relationship between moisture and pH (FIG. 1), between phosphate 
and pH (FIG. 2), between salt and pH (FIG. 3), and between the combined 
weight of salt and phosphate and pH (FIG. 4). The data show a complex 
relationship, but high-moisture, high-pH shelf-stable cheese spread 
compositions can be achieved by appropriate selection of levels of salt 
and phosphate in the preservation system. 
The samples listed in Tables 1a and 1b (below) were then tested. Note that, 
in contrast to trial 11, which exhibited no botulinal toxicity in samples 
exhibiting a moisture content of about 54%, a phosphate level of 0.5%, a 
citrate level of 1.23%, a sodium chloride level of 0.2%, and a lactate 
level of 1.3% in a product having a pH of 5.8 originally, the trial 4 
incubation having the same ingredients and properties except no lactate 
yielded toxicity at 8 weeks, which was confirmed at 12 weeks. 
The trial 6 and 8 incubations, which had initial products exhibiting a 
desirable moisture content of about 54% and a pH of 5.4 and 5.8, 
respectively, also exhibited no toxicity using phosphate levels of 1.5% 
and citrate levels of 1.23 in both, and sodium chloride levels of 0.2 and 
0.7, respectively, whereas, in trial 4, toxcity was observed using 0.5% 
TABLE 1a 
__________________________________________________________________________ 
Summary of moistures, pH, botulinal toxin production, C. 
botulinum MPN, and added levels.sup.a of citrate, NaCl, phosphate of 
processed 
cheese sauce inoculated with C. botulinum and incubated at 30.degree. C. 
for 48 weeks. 
Original Final Added % Botulinal 
Initial MPN 
Final MPN 
Trial 
% Moisture/pH 
% Mositure/pH 
Phosphate 
Citrate 
NaCl 
Lactate 
Toxicity 
(spores/g) 
(spores/g) 
__________________________________________________________________________ 
1 51.5/5.4 
51.3/5.3 
0.5 1.23 
0.2 
-- 1 vial 
473 117 
toxic 
wk 40 
2 53.5/5.4 
52.4/5.3 
0.5 1.23 
0.7 
-- .sup. 0.sup.b 
87 635 
3 51.1/5.8 
ND.sup.c 
0.5 1.23 
0.7 
-- toxic 
407 ND 
wk 16, 32 
4 54.2/5.8 
ND 0.5 1.23 
0.2 
-- toxic 
167 ND 
wk 8, 12 
5 51.2/5.4 
50.2/5.3 
1.5 1.23 
0.7 
-- 0 2,267 133 
6 54.0/5.4 
53.9/5.2 
1.5 1.23 
0.2 
-- 0 2,667 49 
7 51.1/5.8 
50.32/5.6 
1.5 1.23 
0.2 
-- 0 1,533 88 
8 53.7/5.8 
53.2/5.6 
1.5 1.23 
0.7 
-- 0 1,500 45 
9 52.6/5.6 
51.9/5.4 
1.0 1.23 
0.45 
-- 0 340 19 
10 54.0/5.5 
52.5/5.3 
1.0 1.23 
0.3 
-- 0 3,533 97 
11 53.7/5.8 
53.0/5.4 
0.5 1.23 
0.2 
1.3 0 3,200 18 
__________________________________________________________________________ 
.sup.a Percentages are reported on an anhydrous basis of a sodium salt. 
.sup.b 0, no toxic samples detected. 
.sup.c ND, not determined. 
TABLE 1b 
______________________________________ 
Plate count.sup.a and analyzed values for phosphate, sodium chloride 
and citrate.sup.b of processed cheese spreads. 
Plate 
Trial count % Phosphate.sup.c 
% NaCl % Citrate 
______________________________________ 
1. 1.1 .times. 10.sup.3 
1.3 1.44 1.03 
2. 1.4 .times. 10.sup.3 
1.2 1.83 0.89 
3. 1.2 .times. 10.sup.3 
1.3 1.76 1.23 
4. 1.1 .times. 10.sup.3 
1.2 1.46 2.29 
5. 1.2 .times. 10.sup.3 
1.7 1.87 1.42 
6. 8.4 .times. 10.sup.2 
1.6 1.49 1.91 
7. 1.2 .times. 10.sup.3 
1.8 1.33 1.55 
8. 7.5 .times. 10.sup.2 
1.7 1.82 1.07 
9. 1.3 .times. 10.sup.3 
1.5 1.60 1.14 
10. 1.7 .times. 10.sup.3 
1.5 1.60 1.14 
11. 7.2 .times. 10.sup.2 
1.2 1.58 0.86 
Base.sup.c 
ND.sup.d 1.3 ND 0.24 
______________________________________ 
.sup.a Average results for three samples. 
.sup.b Average results for two samples. 
.sup.c Other analyses results included % sorbate, 0.089%; % lactic acid 
.sup.d ND, not determined. 
phosphate. The trial 10 results also show no toxicity in a product having 
an original moisture of 54% and a pH of 5.5, where the incubation was 
carried out in the presence of 1.0% phosphate, 1.23% citrate, and 0.3% 
sodium chloride. 
The results clearly show that manipulation of these parameters can yield to 
a stable cheese product exhibiting a relatively high moisture content of 
about 54% and a relatively high pH of 5.4 to 5.8. 
EXAMPLE 2 
The procedures of Example 1 were repeated, but this time the test 
formulations are summarized in Tables 2a and 2b. 
TABLE 2a 
__________________________________________________________________________ 
Summary of moistures, pH, botulinal toxin production, C. 
botulinum MPN, and added levels.sup.a of citrate, NaCl, phosphate of 
processed 
cheese sauce inoculated with C. botulinum and incubated at 30.degree. C. 
for 48 weeks. 
Original Final Added % Botulinal 
Initial MPN 
Final MPN 
Trial 
% Moisture/pH 
% Moisture/pH 
Phosphate 
Citrate 
NaCl 
Toxicity 
(spores/g) 
(spores/g) 
__________________________________________________________________________ 
1 48.5/5.3 
47.4/5.1 
0.75 1.23 
0.3 
.sup. 0.sup.b 
247 76 
2 52.1/5.3 
50.2/5.2 
0.75 1.23 
0.3 
0 533 6.7 
3 48.6/5.5 
47.8/5.3 
0.75 1.23 
0.3 
0 347 8 
4 52.1/5.5 
50.5/5.2 
0.75 1.23 
0.3 
0 360 5.3 
5 48.7/5.3 
47.1/5.2 
1.25 1.23 
0.6 
0 87 44 
6 52.4/5.3 
52.0/5.2 
1.25 1.23 
0.6 
0 620 173 
7 49.0/5.5 
47.2/5.3 
1.25 1.23 
0.6 
0 133 25 
8 52.2/5.5 
51.1/5.3 
1.25 1.23 
0.6 
0 487 60 
9 50.0/5.4 
49.5/5.2 
1.0 1.23 
0.45 
0 407 180 
10 50.1/5.5 
49.5/5.3 
1.20 1.23 
0.45 
0 1027 220 
11 53.9/5.8 
ND.sup.c 
0.5 1.23 
0.2 
toxic wk 4, 8 
887 ND 
__________________________________________________________________________ 
.sup.a Percentages are reported on an anhydrous basis of a sodium salt. 
.sup.b 0, no toxic samples detected. 
.sup.c ND, not determined. 
TABLE 2b 
______________________________________ 
Plate count.sup.b and analyzed values.sup.a for sodium chloride.sup.c and 
citrate.sup.c of 
processed cheese spreads. 
Trial Plate count % NaCl % Citrate 
______________________________________ 
1. 5.7 .times. 10.sup.2 
1.99 1.11 
2. 5.5 .times. 10.sup.3 
1.73 1.53 
3. 6.0 .times. 10.sup.3 
1.77 1.14 
4. 5.6 .times. 10.sup.3 
2.04 1.03 
5. 6.1 .times. 10.sup.2 
2.15 1.00 
6. 7.4 .times. 10.sup.2 
2.12 1.12 
7. 6.4 .times. 10.sup.2 
1.82 1.29 
8. 6.1 .times. 10.sup.2 
1.82 1.29 
9. 7.1 .times. 10.sup.3 
1.61 1.07 
10. 1.0 .times. 10.sup.3 
1.61 1.17 
11. 1.0 .times. 10.sup.3 
1.76 1.09 
Base ND.sup.d 1.54 0.35 
______________________________________ 
.sup.a Phosphate analysis results not known. 
.sup.b Average results for three samples; values in CFU/g. 
.sup.c Average results for two samples. 
.sup.d ND, not determined. 
Note that the results confirm the findings set out in Example 1 above. In 
contrast to trial 11 of Example 1, which exhibited no botulinal toxicity 
in samples exhibiting a moisture content of about 54%, a phosphate level 
of 0.5%, a citrate level of 1.23%, a sodium chloride level of 0.2%, and a 
lactate level of 1.3%, trial 11, which had the same ingredients except for 
the sodium lactate, was toxic at 4 (confirmed at 8 weeks). 
Also as observed in Example 1, products having original moisture contents 
of 52.1 to 52.4% and a pH of 5.5 exhibited no botulinal toxicity if the 
cheese products were incubated in the presence of 0.75% phosphate, 1.23% 
citrate, and 0.3% sodium chloride (trials 2 and 4) or 1.25% phosphate, 
1.23% citrate, or 0.6% sodium chloride (trials 6 and 8). At certain 
concentration levels, a preservation system containing sodium chloride, a 
phosphate salt, sodium citrate, and, preferably, sodium lactate yield 
superior results in processed cheese spreads exhibiting a relatively high 
moisture level (over 52%) and a relatively high pH (5.4 or higher). 
The above description is intended to enable the person skilled in the art 
to practice the invention. It is not intended to detail all of the 
possible modifications and variations which will become apparent to the 
skilled worker upon reading the description. It is intended, however, that 
all such modifications and variations be included within the scope of the 
invention which is defined by the following claims. The claims are meant 
to cover the indicated elements and steps in any arrangement or sequence 
which is effective to meet the objectives intended for the invention, 
unless the context specifically indicates the contrary.