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OCR for page 55
-Definitions, Purposes,
and Needs for
Microbiological Criteria
A meaningful discussion on the use of microbiological criteria for foods
and food ingredients requires a precise description of terms used when
applying microbiological limits to foods. In this chapter, definitions are
given for the various types of microbiological criteria. In addition, the
purposes and needs for microbiological criteria for foods and food ingre-
dients in the United States are examined. Because controversy exists about
the application of microbiological criteria as quality standards of foods,
attributes of quality amenable to measurement by microbiological criteria
also are examined.
DEFINITIONS
A criterion is a yardstick on which a judgment or decision can be made.
For this report, a microbiological criterion will stipulate that a type of
microorganism, group of microorganisms, or toxin produced by a micro-
organism must either not be present at all, be present in only a limited
number of samples, or be present as less than a specified number or amount
in a given quantity of a food or food ingredient.
Components of a Microbiological Criterion
A microbiological criterion should include the following:
1. a statement describing the identity of the food or food ingredient,
2. a statement of the contaminant of concern, i.e., the microorganism
or group of microorganisms and/or its toxin or of-her agent,
55
OCR for page 56
56 EVALUATION OF THE ROLE OF MlCROBlOLOGICAL CRlTERlA
3. the analytical method to be used for the detection, enumeration, or
quantification of the contaminant of concern,
4. the sampling plan (see Chapter 6), and
5. the microbiological limits considered appropriate to the food and
commensurate with the sampling plan used.
Mandatory and Advisory Criteria
A mandatory limit is one that the food cannot exceed. Food that does
not meet the criterion must be subjected to some action (see Chapter 71.
For example, it may be rejected by the purchaser, destroyed, reprocessed,
sold as an inferior grade, or diverted to a use where the contaminant is
not of concern. Certain mandatory criteria also may result in the loss of
license to process food when limits are consistently exceeded.
Advisory criteria often serve as an alert to deficiencies in processing,
distribution, storage, or marketing. They are not mandatory but permit
judgments to be made when limits are not met.
Types of Microbiological Criteria
The terms standard, guideline, and specification are widely used in the
United States and other nations to describe microbiological criteria for
foods. There appears to be no need for additional terms. The following
definitions of these terms are recommended by the subcommittee for
application by the food industry and governmental agencies in the United
States and will be used throughout this report.
Standard
A microbiological standard is a microbiological criterion that is a part
of a law, ordinance, or administrative regulation. A standard is a man-
datory criterion. Failure to comply with it constitutes violation of the law,
ordinance, or regulation and will be subject to the enforcement policy of
the regulatory agency having jurisdiction.
Guideline
A microbiological guideline is a criterion that often is used by the food
industry or a regulatory agency to monitor a manufacturing process. Guide-
lines function as alert mechanisms to signal whether microbiological con-
ditions prevailing at critical control points or in the finished product are
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DEFINITIONS, PURPOSES, AND NEEDS
57
within the normal range. Hence, they are used to assess processing effi-
ciency at critical control points and conformity with Good Manufacturing
Practices. A microbiological guideline is an advisory criterion in that a
given lot of food exceeding the limit for a nonpathogenic organism would
not be taken off the market or even downgraded. Guidelines may be
mandatory, however, in the sense that food company management and
regulatory agencies may demand that the conditions responsible for per-
sistent microbiological deficiencies be corrected without delay (see
Chapter 71.
·~ ~
Spec~J`cahon
A microbiological specification is a microbiological criterion that is
used as a purchase requirement whereby conformance with it becomes a
condition of purchase between buyer and vendor of a food or ingredient.
A microbiological specification can be either mandatory or advisory.
PURPOSES
Microbiological criteria as described above may be used to assess:
1. the safety of a food,
2. adherence to good manufacturing practices,
3. the utility (suitability) of a food or ingredient for a particular purpose,
and
4. the keeping quality (shelf-life) of certain perishable foods.
Evaluation of the safety of a food may involve tests for the pathogens
or toxins of concern. Alternatively, it may involve tests for indicator
organisms, where a relationship has been shown between the occurrence
of the indicator organism and the safety of the food. For some pathogens
and toxins, the numbers or concentrations present in a food are significant
in that lower figures do not pose a health hazard whereas higher ones do
(see Chapter 41. Examples of criteria broadly meeting the definition of
microbiological standards are those applied to milk and shellfish (US-
DHEW, 1965; USPHS/FDA, 1978~. The purpose of these criteria is to
protect the consumer's health.
The Howard mold count limits as applied to tomato and certain fruit
products are standards that were designed to minimize the amount of
decayed raw produce that might be introduced into such foods. Although
there is now an awareness that certain molds produce mycotoxins, the
mold count standards (Defect Action Levels) were not established to reduce
a health hazard.
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58 EVALUATION OF THE ROLE OF MICROBIOLOGICAL CRITERIA
Criteria often are used for making decisions related to the acceptability
of products since they may measure adherence to Good Manufacturing
Practices. They can also be used to assess the utility of a food or food
ingredient for a specific purpose; for example, canners of fruit products
must limit the number of heat-resistant ascospores of Byssochlamysfulva
in ingredients such as fruit juice concentrates and tapioca starch.
Industry quality control/assurance departments may use microbiological
criteria to monitor the potential shelf-life of perishable foods. Products
with small numbers of spoilage microorganisms are more likely to have
a longer shelf-life than are those with larger numbers. Such results are of
retrospective value: while they do not extend the shelf-life of the lot that
was analyzed, they do alert the processor to problems that must be cor-
rected in order to achieve satisfactory preservation of future production.
NEED FOR ESTABLISHMENT
A microbiological criterion for a food or food ingredient should be
established and implemented in the United States only when there is a
need for it and when it can be shown to be effective and practical. The
criterion must accomplish its objective, i.e., adequately measure the con-
taminants of concern, be technically attainable under commercial condi-
tions by Good Manufacturing Practices, and be administratively feasible.
There are additional factors that should be considered before the need for
a specific microbiological criterion can be established. These should in-
clude (see Chapters 1 and 31:
1. evidence of a hazard to health based on epidemiological data or a
hazard analysis (see also Chapter 41;
2. the nature of the natural and commonly acquired microflora of the
food and the ability of the food to support microbial growth;
3. the effect of processing on the microflora of the food;
4. the potential for microbial contamination and/or growth during
processing, handling, storage, and distribution;
5. the category of consumers at risk;
6. the state in which food is distributed, e.g., frozen, refrigerated,
heat processed, etc.;
7. potential for abuse at the consumer level;
8. spoilage potential, utility, and GMPs;
9. the manner in which the food is prepared for ultimate consumption,
i.e., heated or not;
10. reliability of methods available to detect and/or quantify the mi-
croorganism~s) and toxins of concern (see Chapter 41; and
11. the costs/benefits associated with the application of the criterion.
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DEFINlTlONS, PURPOSES, AND NEEDS
APPLICATIONS OF CRITERIA
Standards
59
Microbiological standards may be useful when epidemiological evi-
dence indicates that a food is frequently a vehicle of disease. Several
factors should be considered before a microbiological standard is estab-
lished. Most important, the standard must attain its stated objective, namely
the elimination or reduction of foodborne disease. (Although potpies have
been involved in outbreaks of botulism, standards related to the presence
of Clostridium botulinum spores in the frozen product would be highly
impractical since in each outbreak, illness was caused by extreme abuse
of the food by the consumer.) Currently existing "implied" microbio-
logical standards for foods should also be considered (see Chapter 1, page
52 note 3~.
A criticism of standards based on fixed numbers of nonpathogenic
microorganisms is that they can result in the recall or downgrading of
significant quantities of what otherwise may be wholesome food. One
means of minimizing this would be the approach used in the Grade A
Pasteurized Milk Ordinance (USPHS/FDA, 19781. Here a given lot is not
automatically rejected when standard plate counts or numbers of coliforms
exceed the prescribed limit, but penalty provisions, which can include
suspension of the permit to process milk, may be instituted on repeated
violations, e.g., when three out of five of the last analyses within a
specified period of time exceed the standard. This system affords the
correction of undesirable conditions with minimal loss of food, and thus
with minimal cost to the consumer.
Guidelines
Microbiological guidelines are used by food processors to monitor the
microbiological condition of raw products, of a food at critical control
points during processing, of process equipment surfaces, and of the fin-
ished product. Industry quality control/assurance departments commonly
establish microbiological limits, often based on many years of experience,
that should be achievable in foods at critical control points or in the finished
product if good manufacturing practices are observed. Results that exceed
these limits serve to signal some divergence from accepted good manu-
facturing practices and may suggest remedial measures. Industry guide-
lines often are of a proprietary nature and may vary from company to
company, even for the same product.
Microbiological guidelines can aid regulatory agencies in the assessment
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60 EVALUATION OF THE ROLE OF MICROBIOLOGICAL CRITERIA
of good manufacturing practices when analyses are conducted in con-
junction with plant inspection. Before this can be done, a relationship
between the microbiology of the food and the factory conditions would
have to be established, usually for each product and process under con-
sideration.
There is a use for published guidelines such as those offered for finished
products at ports of entry by the International Commission on Micro-
biological Specifications for Foods (ICMSF, 1985) and in certain Codex
Codes of Hygienic Practice (see below). When based on good manufac-
turing practices, statistically valid data, or appropriate experience, such
guidelines permit the processor and others to assess the conditions under
which certain foods have been processed and stored.
Specifications
Microbiological specifications are used in the United States to determine
the acceptability of a raw material or finished product in a contractual
agreement between two parties (buyer and vendor). Specifications are
used by governmental agencies to assess microbiological acceptability of
foods purchased for use in government programs. As with other micro-
biological criteria, specifications should be based on relevant background
data and should fill a need.
RELATIONSHIP TO CODEX
With some exceptions, the definitions, components, types, and purposes
of microbiological criteria described in this report are similar to those
published by the Codex Alimentarius Commission (1980, 19811. Codex
microbiological criteria, however, are tied closely to Codex codes of
hygienic practice and Codex concerns are with international commerce,
while the mission of this subcommittee is to address the needs of gov-
ernmental agencies and the food industry within the United States. The
differences noted below stem from this fact.
A Codex microbiological criterion is mandatory when contained in a
Codex Alimentarius Standard. When introduced, it shall not be de novo
but shall be derived from microbiological end-product specifications that
have accompanied Codes of Practice through the Codex Procedure and
have been extensively applied to the food. In addition, a Codex micro-
biological standard "should, whenever possible, contain limits only for
pathogenic microorganisms of public health significance in the food con-
cerned, although limits for nonpathogenic microorganisms may be nec-
essary" (Codex Alimentarius Commission, 19801.
The term "specification" in the Codex "General Principles" document
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DEFINITIONS, PURPOSES, AND NEEDS
61
(Codex Alimentarius Commission, 1980; see also Appendix B) refers only
to a microbiological end-product specification and is intended to increase
assurance that the provisions of hygienic significance in the code have
been met. This Codex document does not contain a definition of a mi-
crobiological specification as a limit to determine the acceptability of raw
materials, ingredients, or foods in contractual agreement between two
parties.
ATTRIBUTES OF QUALITY AMENABLE TO
MEASUREMENT BY MICROBIOLOGICAL CRITERIA
The term quality usually refers to the property, inherent nature, char-
acteristic or attribute, or degree or grade of excellence of something. The
term quality as commonly applied to food summarizes in one word its
desirable characteristics. Quality of a food as perceived by the consumer
can be described as a value related to flavor, color, and texture. It also
includes imperceptible traits such as nutritional and aesthetic values and
safety. Exclusive of discussions of safety, for the purpose of this report,
microbiological aspects of quality include:
1. shelf-life, as perceived by attributes such as flavor and appearance;
2. adherence to good manufacturing practices;
3. utility of a food.
Each of these attributes is measurable to some extent microbiologically;
the decisive question, however, is to what extent. Although subsequent
sections of this report will deal with this question in more detail, some
discussion of the subject is presented below.
The ultimate shelf-life of a perishable product can be estimated to some
degree through the application of microbiological criteria. Assuming iden-
tical storage conditions, a perishable food with a low number of spoilage
microorganisms will have a longer shelf-life than the same product with
larger numbers of such organisms. In practice, products with unacceptable
shelf-life will soon be recognized and rejected by customers in the market
place. Regulatory agency or industry use of microbiological criteria to
grade foods for shelf-life often is an impractical task because of variable
conditions during storage. Furthermore, relationships among common mi-
crobiological parameters such as total counts and coliform counts, and the
shelf-life of a food are inexact. Some types of microorganisms, because
of enzyme systems acting upon the constituents of the food, cause marked
changes in perceptible quality characteristics of a food while others are
relatively inert biochemically and thus produce little change. In addition,
the effect of certain levels and/or types of microorganisms on perceptible
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62 EVALUATION OF THE ROLE OF MICROBIOLOGICAL CRITERIA
quality characteristics often differs from food to food and is also subject
to changes in environmental conditions such as temperature and gaseous
atmosphere.
Lack of adherence to good manufacturing practices can often be related
to levels and types of microorganisms in excess of those present in a
product produced and held under good conditions. The use of poor quality
materials, careless handling, or insanitation may result in a higher bacterial
count in the finished product. However, a heat treatment or other lethal
process can reduce the higher bacterial counts that result from malpractice;
furthermore organisms may die off during storage of frozen, dried, or
fermented foods. Low counts, therefore, do not necessarily indicate good
commercial practices or even food safety. The absence of viable staph-
ylococci in cheese, for example, does not guarantee the absence of staph-
ylococcal enterotoxin. High aerobic plate counts (APC), on the other hand,
do not necessarily mean careless handling or lack of wholesomeness. For
example, ground beef is likely to yield a high APC, but this may merely
reflect the growth of harmless psychrotrophic bacteria during refrigerated
storage.
The relationship between the microbiology of a food and adherence to
good manufacturing practices must be established by conducting repeated
surveys of processing lines to obtain statistically valid data. The critical
control points in the HACCP approach (see Chapter 10) must be identified
and the microbiology of the food at different stages of processing must
be determined. Through these studies, numbers and types of organisms
that characterize the flora of a food produced under a given set of conditions
can be identified and thus provide a basis for the establishment of a
microbiological criterion. Even then, an allowance has to be made for
variations due to differences in processing procedures and equipment.
Finished foods with microbial counts that exceed the criterion might
reasonably be expected to have been mishandled in some manner during
production and/or storage. As pointed out earlier, however, low counts
do not always reflect good manufacturing practices because a lethal step
in the process or significant die-off of microorganisms during storage may
have occurred.
The relationship between good commercial practices and quality often
is a question of aesthetics. A frozen food, for example, might be processed
under conditions of sanitation that a discriminating person would find
objectionable. While these conditions would be reflected in the micro-
biology of the food, the usual quality attributes of nutritional value, flavor,
texture, color, safety, and shelf-life might not be altered.
Microbiological criteria can be useful to determine the utility of a food
or ingredient. The limits for thermophilic spores in sugar and starches to
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DEFINITIONS, PURPOSES, AND NEEDS
63
be used in canning are an example of this application (National Canners
Association, 19681.
In recent years microbiological quality standards have been proposed
for various foods under Section 401 of the Food, Drug and Cosmetic Act
(U.S. Congress, 1938), which authorizes the establishment of standards
of indentity and quality (see Chapter 81. Limits for APC and numbers of
coliforms were based on extensive market surveys. No data were published
that showed a correlation between organoleptic quality of the foods and
the levels of microorganisms, and since the samples were collected from
retail markets, the microbiological findings could not be related to the
quality of the raw product or processing conditions. As a result of such
surveys, FDA has recommended that state and local agencies consider the
adoption of microbiological quality standards for frozen fish sticks, fish
cakes, and crab cakes (FDA, 1980, 19811.
Although microbiological quality standards are not purported to be
related to safety and a consumer might not perceive any effect on quality
due to the high counts, these standards have been justified on the basis
that microbial levels are indicative of (1) the excellence of raw materials
and ingredients used, (2) the degree of control during processing, and
(3) the conditions of distribution and storage (FDA, 1972~. Additional
justifications (FDA, 1976, 1980) were that minimal standards would be
maintained for foods prone to microbial growth or other quality defects,
and that the microbial quality standards would promote honesty and fair
dealing in the interest of the consumer.
A difficulty with microbiological quality standards is that they are pred-
icated on the basic assumption that quality varies inversely with numbers
of microorganisms. This appears to be true only with some foods processed
under certain conditions. Good-quality frozen peas were found to yield
APC figures approximately 20-fold higher than the poor quality, over-
mature product (Pederson, 19471. The former were more tender and thus
more subject to bruising with the release of microbial growth-promoting
juices. With frozen foods, best quality usually is achieved by very rapid
freezing followed by storage of the food at the lowest possible temperature
(USDA, 19601. These also are the conditions that permit the highest
survival of microorganisms. A common means for reducing the number
of viable microorganisms on a food is to expose it to sprays or flumes
containing relatively high concentrations of chlorine. While such treat-
ments improve microbiological quality, other quality attributes may be
affected adversely since chlorine reacts with numerous food constituents
such as amino acids, lipids, and chlorophyll. At present it is not known
whether these different chloro-organic compounds are completely innoc
uous.
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64 EVALUATION OF THE ROLE OF MICROBIOLOGICAL CRITERIA
REFERENCES
Codex Alimentarius Commission
1980 General principles for the establishment and application of microbiological criteria
for foods. Appendix II in Report of the 17th Session of the Committee on Food
Hygiene. Rome: Food and Agriculture Organization.
1981 Report of the 14th session of the Codex Alimentarius Commission. Rome: Food and
Agriculture Organization.
FDA (Food and Drug Administration)
1972 Proposed microbiological quality standards. Federal Register 37(186j:20038-20040.
1976 Standards of quality for foods for which there are no standards of identity. Amendment
and confirmation of effective date. Federal Register 41(154):33249-33253.
1980 Frozen fish sticks, frozen fish cakes, and frozen crab cakes; Recommended micro
biological quality standards. Docket No. 79N-081. Federal Register45(108):37524
37526.
1981 Frozen fish sticks, frozen fish cakes, and frozen crab cakes; Recommended micro
biological quality standards. Docket No. 79N-0081. Federal Register 46(113):31067
31068.
ICMSF (International Commission on Microbiological Specifications for Foods)
1985 Microorganisms in Foods. 2. Sampling for microbiological analysis: Principles and
specific applications. 2nd Ed. In preparation.
National Canners Association
1968 Laboratory Manual for Food Canners and Processors. Vol. 1. Westport, Conn.: AVI
Publishing.
Pederson, C. S.
1947 Significance of bacteria in frozen vegetables. Food Research 12:1-10.
U.S. Congress
1938 Federal Food, Drug and Cosmetic Act of 1938. Pub. L. 717 (June 25) 52 Stat. 1040.
Washington D.C.: U.S. Government Printing Office.
USDA (U.S. Department of Agriculture)
1960 Conference on frozen food quality, Western Regional Research Laboratory. Publi-
cation ARS-74-21. Washington D.C.: USDA.
USDHEW (U.S. Department of Health, Education and Welfare)
1965 National Shellfish Sanitation Program, Manual of Operations. Part 1. Sanitation of
Shellfish Growing Areas. Washington D.C.: U.S. Government Printing Office.
USPHS/FDA (U.S. Public Health Service/Food and Drug Administration)
1978 Grade A Pasteurized Milk Ordinance. 1978 Recommendations. USPHS/FDA Publi-
cation No. 229. Washington, D.C.: U.S. Government Printing Office.
Representative terms from entire chapter:
manufacturing practices
