Microbiological Quality and Safety in Dairy Industry

Module 4. Microbiological risk profile and safety criteria for dairy products

Lesson 19
MICROBIOLOGICAL CRITERIA AND SAMPLING GUIDELINES

19.1 Introduction

Microbiological standards have been set where risk assessment has shown that the risk of food-borne illness associated with the consumption of certain foods is relatively high and that a standard could contribute to the management of the risks identified. Where the justification for a standard was not found, guideline criteria have been developed. These guideline criteria are intended to complement other risk-management strategies undertaken by government and industry. These are mandatory criteria that provide benchmark levels against which unacceptable microbial contamination of food can be identified and remedial action initiated when limits are exceeded. Failure to meet guideline levels generally indicates a failure in the process or hygiene procedures and requires action to identify the cause and remedy the problem.

19.2 Microbiological Criteria

A criterion is a yardstick on which a judgment or decision can be made. A microbiological criterion will stipulate that a type of microorganisms, group of microorganisms or toxin produced by a microorganism must either be not 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.

19.3 Components of a Microbiological Criterion

A microbiological criterion should include the following:

1. A statement describing the identity of the food
2. A statement of the contaminant of concern, i.e. the microorganisms or group of microorganisms and/ or toxin or other agent
3. The analytical method to be used for the detection, enumeration, or quantification of the contaminant of concern
4. The sampling plan
5. The microbiological limits considered appropriate to the food and commensurate with the sampling plan

19.4 Types of Microbiological Criteria

19.4.1 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 e.g., 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 judgment to be made when limits are not met.

19.4.1.1 Standards

A microbiological standard is a microbiological criterion that is a part of a law, ordinance, or administrative regulation. A standard is a mandatory 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.

19.4.1.2 Guidelines

A microbiological guideline is a criterion that often is used by the food industry or a regulatory agency to monitor a manufacturing process. Guidelines function as alert mechanisms to signal whether microbiological conditions prevailing at critical control points or in the finished product are within the normal range. Hence they are used to assess processing efficiency at critical control points with GMP. A microbiological guideline is an advisory criterion in that a given lot of food exceeding the limit for non-pathogenic organisms would not be taken of 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 persistent microbiological deficiencies be corrected without delay.

19.4.1.3 Specifications

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.

19.5 Microbiological Criteria for Acceptance or Rejection of Sample Lots

1. the food which must comply with the microbiological limits set in relation to that food;
2. the microorganism or group of microorganisms of concern;
3. the number of sample units to be taken and tested;
4. the level of microorganisms considered acceptable, marginally acceptable or critical (depending on the sampling plan specified) and
5. The number of samples that should conform to these limits.

19.6 Sampling Plans and FSSAI Microbiological Standards for Milk and Milk Products

Sampling plan and interpretation: The following terms, as used by the International Commission on Microbiological Specifications for Foods (ICMSF) are defined and used in development of FSSAI standards for different milk and milk products.

n = the number of sample units which must be examined from the batch/lot of food to satisfy the requirements of a particular sampling plan.

c = the maximum allowable number of defective sample units. This is the number of sample units, which may exceed the microbiological limit specified by m. These are considered marginally acceptable results provided they did not exceed the limit specified by M. When more than this number is found; the lot is rejected by the sampling plan.

m = Represents an acceptable level and values above it are marginally acceptable in terms of the sampling plan.

M = A microbiological criterion which separates marginally acceptable quality from unsatisfactory/potentially hazardous quality. Values above M are unacceptable in terms of the sampling plan and detection of one or more samples exceeding this level would be cause for rejection of the lot.

When 5 or more units of the same variety from a lot or consignment are analyzed (n = 5), no more than 2 units (c = 2) should exceed the maximum tolerance (m) for microbiological levels stated in the reference criteria and no 1 unit should exceed the stated level for the maximum tolerance (M).

Microbiological criteria and their interpretation: Three categories of microbiological quality have been assigned in standard based on Total plate count, levels of indicator organisms (Coliform count and yeast & mold count) and the number or presence of pathogenic bacteria. These are satisfactory, unsatisfactory and potentially hazardous.

1. Satisfactory: if a maximum of c/n value are between m and M, and the rest of the values observed are < m ---- means the results are within limits of acceptable microbiological quality and no action is required.
2. Unsatisfactory: If one or more of the values observed are >M or more than c/ n values are between m and M means the results are outside acceptable microbiological limits linked with hygiene indicators (Total plate count, Coliform count and Yeast and mold count) and are indicative of poor hygiene or poor handling practices. Under these conditions the premises producing such unsatisfactory product shall be stopped and will carry out the detailed investigations for nonconformity/ noncompliance during manufacturing. The manufacturing of such product will be re-started only after HACCP/ GMP audit clearance of the premises by the food safety authority and compliance of fresh product with the regulatory limits.
3. Potentially hazardous: If one or more of the values observed are >M or more than c/ n values are between m and M means the results are outside acceptable microbiological limits linked with pathogenic bacteria (E. coli, Salmonella, coagulase positive S. aureus, B. cereus, C. perfringens, L. monocytogenes) and are indicative of serious food safety concern and immediate remedial action should be initiated. Such results will attract enforcement/ prosecution by the concerned food safety authorities. Withdrawal of any of the food still available for sale or distribution and if applicable, recall action may be initiated. An investigation of food production or handling practices shall be investigated to determine the source/ cause of the potential of the problem so that remedial action can commence. A detail risk assessment shall also be done. Failure by an owner to either cease manufacture of product or withdraw/ recall product from sale when requested to do so shall result in seizure of that product where the officer has reason to believe that it is contaminated with pathogenic bacteria.

19.7 Sample Size, Storage and Transport Standards & Reference Methods of Testing

Each sample unit taken for submission to the laboratory should be of sufficient size to allow the appropriate analysis or analysis to be carried out and should, preferably, be much larger than the analytical size needed to allow for further testing if required. A minimum sample size of 100 g or 100 ml is usual. Food samples obtained by an authorized officer as a result of a consumer complaint, or as part of an investigation of a suspected food poisoning incident, may only be single samples. While this is less than the five sample units generally prescribed, the results of an analysis on such a sample is still considered valid. Food samples provided to the testing laboratory should have undergone only minimum change in their microbiological status since the point of sampling. It is very important, for example, that samples are not contaminated during the process. Knowledge of aseptic sampling techniques and the use of appropriate sampling tools may therefore be necessary.

It is also important that the temperature during transport and storage of the food samples is appropriate to minimize microbial growth. Chilled foods should, for example, be transported in an insulated container and frozen foods kept frozen. Every effort should be made to minimize the period between sampling and analysis. The sampling for microbiological testing as per the sampling plan in the standards is to be ensured at manufacturing units as per the guidelines given in IS: 11546:1999 (ISO 707:1997). The samples are to be stored, transported as per the guidelines proposed in Table 19.1 and processed for different microbiological parameters as per the approved test procedures given in Table 19.2 from an accredited laboratory within 24 hours of sampling. Otherwise even under cold storage conditions some psychrotrophic microorganisms can grow and change the microbial status of the food product. Preservatives shall not be added to samples intended for microbiological examination as being practiced for chemical testing. Product samples in duplicate (minimum) are to be tested from the different accredited laboratory. The final decision is to be drawn based on two test results obtained from the accredited lab.

Table 19.1 Guidelines for sample size, storage & transport temperature for milk & milk products

Table 19.2 Reference test procedure for different microbiological parameters proposed in draft standards

Note: ¹A lot means a quantity of food, which is prepared or packed under essentially the same conditions, usually:

• From a particular preparation or packing unit; and
• During a particular time ordinarily not exceeding 24hours

A lot of food does not comply with the standards if the number of defective samples units is greater than c, or the level of a microorganism in a food any one of the sample units exceeds M. sampling plans for different milk and milk products are presented in the format used by ICMSF.