Fuctions of Micro-organisms in Foods (Food Microbiology lecture 6)

Functions of Microorganisms in Foods

Microorganisms in foods perform four major functions. These functions can be 

categorized into three broad functions. These are:

1. Non-useful functions: 

i. Food Spoilage: The spoilage microbiota consists of microorganisms that can 

grow on a food, causing undesirable changes. The potential of micro- organisms 

to spoil food rests on their ability to produce metabolites that are associated with 

spoilage. The growth of spoilage microorganisms in foods may result in changes 

in sensory properties, such as colour, odour, texture, and appearance.

Spoiled foods may be safe to eat, i.e. they may not cause illness if there are no 

pathogens or toxins present, but changes in texture, odour, taste, or appearance 

may cause them to be rejected.

ii. Food Borne Diseases: Microbial foodborne illness is often divided into two 

broad categories: food intoxication and food infection. 

a) Food intoxication: This occurs when the pathogenic microorganism 

secretes a toxin in the food prior to consumption. Eating the food that 

contains the toxin disrupts a particular target, such as the gastrointestinal 

tract or the nervous system. The symptoms of intoxication vary from bouts 

of vomiting and diarrhea to severely disrupted muscle function, as with 

botulism. Botulism is a rare but serious illness caused by a toxin that 

attacks the body’s nerves and causes difficulty in breathing, muscle 

paralysis and even death. This toxin is made by Clostridium botulinum

and sometimes Clostridium butyricum and Clostridium baratii bacteria.

b) Food infection: Foodborne infection is caused by ingestion of food 

containing live microbes which grow and establish themselves in the 

human intestinal tract. This occurs when the microorganism multiplies in 

food until it reaches the minimum infective dose (MID), which is the 

number of microorganisms needed to cause illness in humans. When the 

food is ingested, the microorganism acts directly on the intestines. In some 

cases, the microbes infect the surface of the intestine; in other cases, they 

invade the intestine and other body structures. Most food infections result 

in some degree of diarrhoea and abdominal distress. 

In food infection, microbes growing in the infected tissue can release 

toxins, unlike food intoxication, where the toxins are already present in 

the food and the presence of live microbes is not required.

**Food poisoning is a general term usually referring to a gastrointestinal disease 

caused by the ingestion of food contaminated by pathogens or their toxins.

2. Useful functions:

i. Food Processing: Nature uses microorganisms to carry out fermentation 

processes, and for thousands of years mankind has used yeasts, moulds and 

bacteria to make food products such as bread, beer, wine, vinegar, yoghurt and 

cheese, as well as fermented fish, meat and vegetables; Saccharomyces cerivisiae

is used in the production of many fermented beverages e.g. wine, beer and cidar, 

Yeasts (Candida rugosa, Kluyveromyces marxianus) and lactic Acid Bacteria 

ii. Food Preservation: The use of non-pathogenic microorganisms and/or their 

metabolites to improve microbiological safety and extend the shelf life of foods 

is defined as bio-preservation. It can be defined as the extension of shelf life and 

food safety by the use of natural or controlled microbiota and/or their 

antimicrobial compounds.

There are also Inert function: The microorganisms present in the foods are 

neither useful nor non-useful. The inert microorganisms do not find the 

environment favourable for growth.