3.1 Introduction

Unit 3 - Enumeration of microorganisms in foods

3.1 Introduction
The raw, semi-processed and processed foods as well as the ingredients used in the preparation of processed foods may contain several microorganisms. The microbial examination of foods is generally done to know the presence or absence of specific microorganisms, types of microorganisms, number of microorganisms and their products in foods. The information on the microorganisms associated with food will help in;
Estimating shelf life (suitability for human consumption) by determining microbiological quality of a food or constituent of food.
Identifying the cause of spoilage or presence of pathogens, when food is implicated in food borne illness.

Methods of enumeration
Several methods are available for the enumeration of microorganisms from food. These can be broadly divided in to direct methods or indirect enumeration methods based on whether the microorganisms are counted directly or the products released by them is estimated.

I. Direct enumeration methods

a. Direct counting methods
  • Direct microscopic count (DMC)
  • Direct counting on membrane filters
b. Culture based methods

Plate count method
  • Pour plate method
  • Spread plate method
Most probable number (MPN) technique

II. Indirect enumeration methods

a. Alternative Methods (chemical and physical methods)
  • Dye reduction test
  • Electrical methods
  • ATP determination
b. Rapid Methods
  • Immunological methods
  • DNA/RNA methodology

Last modified: Monday, 23 May 2011, 10:32 AM