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MPM: I. Introduction

Macroanalytical Procedures Manual (MPM) Main Page


  1. Definition of Macroanalytical Methods
  2. Advantages and Limitations of Macroanalytical Methods
  3. Scope of the Macroanalytical Procedures Manual
  4. Legal Aspects
  5. Determination of Defects
  6. Sampling Methods

(1) Definition of Macroscopic Methods of Analysis (I-1)

"Macroscopic" analysis of a product refers to an evaluation of the substance through the use of the unaided senses (primarily sight, smell, or taste) of an individual. Every consumer in our society who exercises some judgment in the purchase of foods, cosmetics, and other consumer goods, knowingly or unknowingly conducts some form of macroscopic examination to detect apparent or obvious defects. In the case of foods, this usually occurs upon purchase or utilization of the product. The examination may range from a cursory, perhaps unconscious visual check of the product to confirm that everything "looks right" to a much more detailed scrutiny to check for specific defects. The scene at the fruit stand where the careful shopper squeezes and sniffs the produce prior to purchase is probably repeated thousands of times daily across the country. This is typical consumer macroscopic examination.

Regulatory authorities, in fulfilling responsibilities for protecting the public health and safety, conduct more systematic examinations to disclose not only apparent defects but also hidden defects. Over the years, standardized methods of macroscopic examination have evolved for determining filth, decomposition, and foreign matter in foods, drugs, and cosmetics and other products subject to the laws enforced by the U.S. Food and Drug Administration. These methods of analysis have evolved with the input of producers and consumers as well as regulatory authorities.

The objective of this manual is to compile and organize in one volume the standardized methods of macroscopic analysis which are useful in determining defects in various types of foods. Although in a general sense, the term "macroscopic" is not as broad as the term "macroanalytical," for the purposes of this manual, the terms are used interchangeably.

(2) Advantages and Limitations of Macroanalytical Methods (I-1)

"Macroscopic" or macroanalytical methods for examination of a food generally depend upon the direct sensory input of the analyst as the primary means of detecting defects. For example, visual examinations are typically conducted with the naked eye; occasionally this may be supplemented by low power magnification to confirm defects observed first with the naked eye or to describe them in greater detail.

There are several major advantages to the use of macroanalytical procedures. They are inexpensive and require little specialized equipment. They generally permit the analysis of a large quantity of product in a relatively short period of time and thus allow the analyst to assess the overall condition of the lot quite rapidly. The analyst can quickly identify and isolate those portions of the lot which may contain defects and thus limit the amount of material which may need a more detailed, microscopic evaluation.

Although macroscopic methods have many positive aspects, they may not be the method of choice for every analytical situation. In fact, the very features which add to their usefulness may also limit their application in some situations. Because macroscopic procedures deal with defects which are discernible to the unaided senses, they are not appropriate for defects hidden from the senses such as those too small to be visible to the eye or those obscured through processing or other factors. In such cases, microscopic methods are essential for characterizing and evaluating the defects in the sample.

Microscopic methods of analysis involve the detailed examination of a very small portion of the sample; these procedures have been designed to provide a different type of information than macroscopic methods. They are used to describe and quantify defects on a different scale than macroscopic methods can and to identify "hidden" defects that cannot be detected through a gross evaluation of the sample. However, microscopic methods also have limitations; they tend to be more time-consuming and more expensive, and they require more specialized equipment. Also, because they are limited to the analysis of a very small sample, the results are not always representative of the overall condition of the lot.

It is apparent that macroscopic and microscopic procedures for characterizing defects in foods tend to supplement each other, and together provide a comprehensive evaluation of defects in the product. It is important that the analyst realize the close association of the macroscopic and microscopic methods for use as a joint approach in solving analytical problems.

(3) Scope of the Macroanalytical Procedures Manual (I-2)

This manual is intended to compile standardized macroanalytical procedures for identifying defects in food products. However, as discussed in the previous section, macroscopic procedures are frequently interrelated with and supplemented by microscopic ones, each providing the analyst with a different type of information. For this reason, the Macroanalytical Procedures Manual will refer to microscopic procedures in some situations. These microscopic procedures may be grouped in three categories:

  • Microscopic methods which have been published by the Association of Official Analytical Chemists in Chapter 16 ("Extraneous Materials") of the Official Methods of Analysis. Where required, this manual simply refers the analyst to the applicable section of the AOAC volume for the appropriate method.
  • Microscopic methods which have been published in the AOAC volumes, but which must be adapted by the analyst for a particular situation. In these cases, special instructions are provided in this manual so that the analyst can modify the microscopic procedure as necessary. Reference is made to the appropriate section of the AOAC.
  • Microscopic procedures which have been developed and are in use, but have not been subjected to collaborative study and thus are not yet published by the AOAC. These procedures are included in full in this manual so that they are not lost to the analyst.

Thus, when using this manual, the analyst may be instructed to combine both macroscopic and microscopic techniques. Examples of this can be seen in the method for determining decomposition in frozen strawberries, which utilizes macroscopic "pick-out" of defects (see Chapter V, Section 9.N.(4)b.) supplemented by the microscopic mold count technique (Chapter V, Section 9. N.(4)c.). Information provided by the microscopic techniques will aid the analyst in interpreting and evaluating the macroscopic findings and in determining the overall quality of the food.

(4) Legal Aspects (I-2)

The methods described in this manual are part of FDA's regulatory program to ensure that foods and other commodities are safe for human consumption. This regulatory program derives in part from Sections 402(a)3 and 402(a)4 of the Federal Food, Drug, and Cosmetic Act (FD&C Act) which deal with adulteration of food. Chapter III of the same act prohibits the manufacture, sale, and distribution of adulterated foods. Pertinent rules, regulations, guidelines, advisory opinions, and other notices issued under the statutory requirements of the FD&C Act provide further details on implementation and enforcement of these sections. The "Applicable Documents" section for each method refers to appropriate information for the particular foods covered by that method.

  1. Adulteration of Foods -- Many of the defects in foods and other commodities which are addressed by macroscopic methods are the result of attack by pests such as rodents, insects, molds, etc. These attacks encompass practically any living stage of animal or plant life which can directly or indirectly injure, cause disease or result in damage to food or other material. Defilement of a food by pests or contamination by other sources of extraneous foreign matter may render the food adulterated under section 402(a)3 of the FD&C Act. That section states that a food shall be deemed to be adulterated "if it consists in whole or in part of any filthy, putrid or decomposed substance, or if it is otherwise unfit for food." Thus the presence of macroscopic defects such as insect-damaged, moldy, animal-contaminated, rancid, and dirty material may comprise sufficient grounds to consider the food adulterated. Moreover, under Section 402(a)4, food shall be deemed adulterated "if it has been prepared, or packed or held under insanitary conditions whereby it may have become contaminated with filth, or whereby it may have been rendered injurious to health." Hence, to be adulterated, food need not be shown actually to contain filth or other contaminants; a demonstration that the food was prepared, packed, or held under conditions whereby it would, with reasonable possibility, become so is legally sufficient to prove adulteration and provide grounds for taking action against the lot. Macroscopic examination of factory samples and exhibits may provide such evidence.
  2. Defect Action Levels -- Defect action levels are limits set by FDA to define the extent of contamination acceptable in food. The action level represents the limit at or above which FDA will take legal action against a product to remove it from the market as adulterated ("unfit for food"). To be equitably administered, each individual Defect Action Level must be coupled to an acceptable standardized method for determining compliance or non-compliance with the specific Defect Action Level. This manual provides descriptions of such standard procedures for determining the extent of macroscopic defects in food such that legal action can be taken if appropriate.

    The FDA listing of "Food Defect Action Levels," which covers many of the products contained in this manual, includes approximately 200 action levels for various types of defects in some 75 individual food products. These levels have been established in recognition that it is not now possible, and never has been possible, to grow, harvest, and process crops that are totally free of natural defects. Accordingly, through the years, the FDA has established levels for natural or unavoidable defects in certain foods consistent with the technological capabilities of the affected industry and with acceptable standards of safety and security.

    It should be noted that the regulation relating to Defect Action Levels (21 CFR 110.110) clearly states that compliance with defect action levels does not excuse failure to observe two other important requirements of Section 402(a)4:

    • Food may not be prepared, packed or held under insanitary conditions
    • Food manufacturers must observe current good manufacturing practices.

    Thus, evidence obtained during factory inspections which indicates such a violation may lead to finding that the food is adulterated, even though the amounts of natural or unavoidable defects are lower than currently established action levels. According to the regulation, "The manufacturer of food must at all times utilize quality control procedures which will reduce natural or unavoidable defects to the lowest level currently feasible."

(5) Determination of Defects (I-4)

Each of the methods contained in Chapter V describes procedures to be followed in the examination of a particular food or commodity. Based on the results of this examination, a determination is made as to whether or not the material is "fit for food," using the Defect Action Level established by FDA as the standard. Particular defects which are likely to result in a determination that a given lot or shipment of material is not passable are described in Chapter V as a subsection of the method for that food item. This part of the introduction presents a discussion of two points which bear general relevance to the determination of defects by using macroanalytical methods.

  • Sources of defects (field vs. storage)
  • Discrimination between signs and symptoms of defects

For a more extensive discussion of defects in food, see Chapter 3, "Sources of Food Contaminants" in FDA Technical Bulletin No. 1, Principles of Food Analysis for Filth, Decomposition, and Foreign Matter, 2nd edition.

  1. Sources of Defects (Field vs. Storage) -- Insects, molds, and rodents are the principal causative agents for most of the defects covered by macroanalytical methods. In general these agents may be classified as either "field" or "storage" pests. In the field or orchard, a food commodity is more likely to be susceptible to different pest attacks than it is after harvest or during storage. During its movement from farm to the processor and through distribution channels, environmental conditions surrounding the commodity change significantly. Because of the different habitats, different species of organisms challenge the product's integrity.

    It may be important for the analyst to distinguish between these two types of defects. For example, the Method for Dried Fruits (Chapter V, Section 9.F.) specifies that field and storage insect infestation be reported separately. In many cases, these terms distinguish between pre- and post-harvest defects. Many of the defect action levels involve pre-harvest damage to crops from insects, fungi (molds), field rodents, birds, and other pests that are not completely avoidable under good agricultural practice. Processing of the commodity provides an opportunity to eliminate or control the extent of these defects through inspection, sorting, cleaning, and other steps to ensure production of an acceptable product. Because of this, field or orchard defects are different from defects which occur during processing under the close surveillance of the manufacturing establishment. Raw materials or ingredients stored on the premises of a processing facility should be maintained under controlled conditions so as to prevent spoilage, protect against contamination, and minimize damage.

    The distinction between field and storage defects, however, is not always sharply defined. In some instances, the same species of organism may attack the product in the field as well as in storage (for example, see the Method for Peas and Beans, Chapter V, Section 11.G.). Some produce may remain in the field or the orchard for further drying and/or holding (for example, the sun-drying of fruits). Thus, it is susceptible to the same pests since conditions have not changed.

    Macroanalytical methods of analysis therefore should include an identification of the sources of defects to the maximum extent possible. Such information may be useful not only in evaluating the acceptability of the product for consumption but also in assessing responsibility for identifying weaknesses in quality control or preventive sanitation programs.

  2. Signs and Symptoms of Defects -- It may be convenient to understand the defects in foods covered in this Manual as comprising a combination of "signs" and "symptoms." "Signs" refer to the direct causal agents of the defect while "symptoms" are the adverse effects observable in the product material. For example, the sign could be the presence of the specific causal factor, such as a species of fungi, bacteria, virus, insect, rodent, bird, nematode, or other pest. The symptom or observable adverse effect in the product may take various forms, such as different degrees and types of decomposition, tissue breakdown, lesions, or other abnormal conditions. In some instances, the symptom per se can conclusively identify the causal factor. For example, the circular, light brown, decayed lesions of "brown rot" on peaches are unique to Monilinia fructicola (Wint.) Honey. In this case, the sign or fungus is also present. It can be detected macroscopically and then identified or confirmed microscopically. If the fruit is pulped, however, the symptoms may be completely masked, leaving only the microscopic sign as evidence of its presence. The Method for Coffee Beans (Chapter V, Section 1.A.) illustrates vividly the signs and symptoms associated with the two species of insects that commonly attack green coffee beans.

Sensitivity to sources of various defects as well as an understanding of the distinction between signs and symptoms of defects provide a basis for evaluating important clues. Accurate evaluation of these clues in turn improves the significance of analytical findings.

(6) Sampling Methods (I-5)

The ultimate responsibility of the analyst is to determine the acceptability or unacceptability of a given lot or shipment of food material based upon his or her examination. For reasons of time and cost, it is clearly impractical for the analyst to examine every item in a shipment or lot. Thus the analyst must limit detailed examination of material to a sample collected from the lot. Since decisions about regulatory action are therefore necessarily made by extrapolation, it is important that sampling techniques used by inspectors are consistent with statistical theory.

Two sampling techniques, representative and selective sampling, are used in conjunction with the methods in Chapter V. These are discussed below.

  1. Representative Sampling -- Representative sampling is an objective sampling technique used when the sample of the material has been selected to maximize the probability that it contains the same proportion of defects as the entire lot. That is, the analyst wishes to make a determination about the condition of the entire lot. To assure this, a representative sample must always be drawn by using random selection. Random selection or sampling is sampling from a population such that each element is the population has an equal probability of being selected for inclusion in the sample.

    Another important element in representative sampling is size. The larger the sample size, the higher the probability that the representative sample contains the same proportion of defects as the entire lot. If perfect certainty were required, clearly the entire lot should be sampled. Statistical theory allows the analyst to work with relatively small representative samples while maintaining quite high levels of certainty that determinations made on the basis of the examination of a sample are accurate reflections of the condition of the entire lot. As an example of the power of statistical inference, consider the accuracy of prediction about Presidential election results. These projections are usually accurate to within a few percentage points but are based on samples of only a few thousand voters.

    When the analyst uses methods in this manual, questions of sample size and levels of certainty have been resolved in advance by agency statisticians applying the concepts of acceptance sampling. Decision rules about when to accept or reject an entire lot have been incorporated into the methods in Chapter V. Sampling plans called for in the manual are specified at the beginning of each procedure. The plan usually calls for a fixed sample size. Some procedures allow the analyst to examine the material in an iterative fashion using a sequential sampling plan. For sequential sampling, the decision rules indicating when to accept, reject, or continue sampling are built into the plan. For fixed sampling plans, the "Report" section of the procedure indicates when to accept or reject a lot. In some instances the lot sample itself may be so large that the analyst cannot effectively examine the entire sample. In this situation, unless evidence of defects dictates that the entire sample should be analyzed, an analytical sample must be taken by the analyst for examination. The analyst's responsibility here is to ensure that the analytical sample is representative of the lot sample. The sample preparation section of each procedure provides guidance as appropriate. (For example, in Chapter V Section 3.A, the procedure for determination of insect-damaged wheat kernels calls for use of a Jones sampler or Boerner divider to reduce the size of the lot samples to representative analytical units.)

  2. Selective Sampling -- Selective sampling is a subjective sampling technique where materials are drawn to confirm a suspected defect. Unlike representative sampling where material is drawn at random to assess the general condition of a lot, this technique is deliberately biased. It is used in cases where the task of the analyst is to confirm the presence of suspected defects. In these situations, representative sampling could result in the dilution of the contaminant to a point below the practical limits of measurement of a macroscopic method. Macroscopic examination of import samples, on the wharf, factory samples, or exhibits of defiled food material submitted for macroscopic examination are usually drawn by using selective sampling. For example, inspection of a food production facility may disclose damaged bags of dried beans with characteristic fluorescent rodent urine stains on the surface of the bag. The fluorescent material, often caked, and the adjacent beans are the best sample for use in laboratory verification of the presence of urine or related defects. Another example in which selective sampling would be appropriate is in sampling a shipment of bulk food material from the hold of a ship suspected to have previously carried a poisonous ore; portions of the shipment from the bottom of the hold would comprise the appropriate sample. Similarly, in a shipment of cocoa beans, any water-damaged bags are more likely to be attacked by molds than are sound bags. Thus an unrepresentative sample selected from the wet bags is the appropriate material to be sent to the laboratory for examination to confirm adulteration.

Because sampling is a practical necessity, an understanding of sampling techniques is important to the methods described in this manual. The two sampling techniques discussed here, representative and selective sampling, each play a significant part in application of these macroanalytical procedures to determine whether a lot meets regulatory standards.

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