Quantitative Methods used to Determine Spoilage Microorganisms

Indicator organisms are microorganisms used to test for pathogens by introducing them into the body as markers. They indicate similar pathogens by indicating that the numbers are more than the numerical limits expected. Quantitative testing usually shows whether the food has undergone adequate processing and the quality of the food substance. Lacking the ability to maintain foodborne contaminants such as microbial toxins, food spoilage organisms, indicator organisms, and foodborne pathogens makes it challenging to trace food from when it is raw throughout the processing to consumption stage.

The indicator organisms can be divided into four categories as follows:

  • Metabolic products of pathogens that show health hazard
  • Those that determine the exact number of microorganisms and microbial activity
  • Those that indicate contamination during the post-heat processing stage
  • Those that demonstrate the potential presence of fecal contamination or pathogens

Food quality and food safety assessment involves the enumeration and detection of pathogens and spoilage microorganisms in consumable food products. The conventional testing methods can produce qualitative and quantitative results when identifying the type of pathogens present in a food sample.  Quantitative assessment of microorganisms focuses on the determination of the microbial cell concentration in a sample. The methods used usually involve establishing the bacterial count by first culturing and developing the bacteria on a plate then counting the number of colonies present in each ml or gram of the sample.

Quantitative methods are used to determine the number of microorganisms in a sample. The methods used for counting food microbes include

  1. Direct Cell Count

The counting of microbial cells in food can be done by placing the sample directly under a microscope or using an electronic particle counter. Microscopic counting is done by measuring a specific amount of sample and into a slide and counting the number of pathogens by determining the microscopic fields and relating them to the volume area properties of the surface. The other method used is applying fluorescent dyes to stain all the present bacterial species in a sample. Once the bacteria have been stained, they are observed under UV light, making them fluoresce orange and be counted.

  1. Indirect Count of Cells

This method of enumeration of bacterial counts involves the dilution of the sample, after which the sample is cultured in a medium before estimating the number of bacteria present. One of the methods used is called the viable count. A viable plate is needed in which the samples that have been diluted are placed before the bacterial sample is incubated. The number of colonies is then counted depending on the dilution factor.

  1. Measurement of the Bacterial Cell Mass

This method estimates the number of present bacteria by determining the cell mass of all the cells. The biomass of the bacteria present in a sample can be related to the number of cells by analyzing the wet weight and the dry weight. An indirect measurement method can also be employed in which the estimation of microbial cells is done by assessing the proteins, ATP, chlorophyll, or lipopolysaccharides.


Microorganisms usually cause adverse health problems and fast food spoilage. Hygiene is paramount when it comes to handling consumable food products. Therefore, control and maintenance methods are necessary to ensure that the production and processing stages are free from any contamination by microbes. By counting the total number of bacteria present in a food sample, we can tell the type of hygiene management in a company. Several methods can be employed in the counting of microbial species present in a food sample.

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