Читать книгу Analytical Food Microbiology - Ahmed E. Yousef - Страница 50

How can one evaluate the microbiological quality of a food? Enumeration of microorganisms in the food is the answer that often comes to mind. The important follow up question then is: Can this enumeration be done accurately so that the results are used reliably to measure the microbiological quality? Reliability of the results, obviously, depends on how the enumeration is executed. This chapter addresses this topic with the goal of familiarizing the analysts with the methods and techniques used in enumeration and helping them apply these to produce repeatable and reliably results.

Foods vary in microbial load depending on how they are produced, processed, transported, stored, and handled. Microbial load, which is sometimes referred to as microbial burden, bioburden, or microbiota, is made of a predominant microorganism, a group of microorganisms having common characteristics, or a number of unrelated microorganisms. Determining the microbial load involves counting or enumerating the population of microorganisms in the food. “Counting” or “enumeration” in food microbiology refers to process of determining the concentration of a population of a microorganism (or microorganisms) of interest in a food. The counting exercise, therefore, determines the number of microbial cells, the number of colony forming units (CFU), or the most probable number of CFU present in a unit volume, weight, or surface area of a given sample. There are several methods used in counting or enumerating microbial populations in food. Counting using the “plate count” and the “most probable number” methods will be discussed, as these are the primary means of enumeration presented in the remainder of this book. Other counting techniques are also used in quality control laboratories (e.g., direct microscopic count and spiral plating); however, these techniques will not be discussed in this chapter.