Effect Of Microorganisms On Food Quality And Safety

Project and Seminar Material for Microbiology

Effect Of Microorganisms On Food Quality And Safety

Chapter One

1.0 Introduction

Every food harbors its own microbiota that may be specific and characteristic of a given point in the production process and of storage conditions. In processed foods, the microbiota consist of microorganisms from raw materials that survived the processing, preservation and storage conditions as well as microorganisms that contaminate the foods during handling and processing (Ternstrom et al., 2003). In raw foods, their characteristics handling and environmental conditions as well as farming practices will dictate the predominating microbiota.

Some microorganisms can be considered useful, if the changes due to their growth in foods are deemed beneficial, for example, in terms of flavor, texture and appearance. But microorganisms can also be able to spoil foods. From the point of view of sensory rejection (deterioration), the spoilage microbiota consists of microorganisms that can grow on a food, causing undesirable changes. The potential of microorganisms to spoil food rests on their ability to produce metabolites that are associated with spoilage and that will lead to rejection of foods by consumers. In general, many microorganisms in a food are capable of producing undesirable metabolites when they grow above a certain level (Gram et al., 2002). The growth of spoilage microorganisms in foods may result in changes in sensory properties, such as colour, odour, texture and appearance. Additionally, some microorganisms pose a health risk and they are considered pathogenic. The characteristic of the disease will depend on a number of factors inherent to the food, pathogenic microorganism and affected individual. There are many microorganisms that are naturally present in foods, sometimes as contaminants. Bacteria stand out the most, both as pathogens and as spoilage microorganisms. For example Psedomonas species and other Gram – Negative Psychrotrophic microorganisms can be responsible for reduction of shelf life of high – protein, chilled foods stored under aerobic conditions, such as meat and dairy products. Pseudomonas is associated with post – processing contamination of pasteurized milk (Eneroth et al., 2000). Shewanella putrefaciens is an example of Psychrotrophic microorganisms responsible for the deterioration of chilled sea-food (Chai et al., 2006). Although vegetative forms of microorganisms play a vital role in food spoilage, spore – forming bacteria are of great relevance for processed foods, such as canned foods, vacuum – packaged meat, and thermally processed foods, because their spores survive lethal treatments (Ternstorm et al., 2003).

In addition to bacteria, fungi are very important group to be concerned with. Fungi are involved not only in food production but also in their spoilage and mycotoxin production, which may have several diverse effects to human and animal health. Viruses, protozoan and parasites play a major role as causes of foodborne diseases in several countries. These microorganisms have variable resistance to lethal treatments used in food processing. Although they all share a common characteristic of not being able to grow in foods, they may be able to survive in these substrates.

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Microorganism or microbe is an organism that is microscopic in nature (invisible to the naked eye and can only be seen with the aid of a microscope). Microorganisms can be bacteria, fungi, archaea or protist. Microorganisms have useful applications such as in food production, treatment of waste water, creation of biofuels and a wide range of chemicals and enzymes.

Microorganisms are found everywhere in our environment. Many types can be found in air and dust and can contaminate food at any time, during food preparation or when food is left uncovered. Microorganisms contaminate food through different sources such as; water, air, soil, spoilt raw materials, biofilms on the surface of equipment and personal hygiene of food workers. Most food serve as a good growth medium for many different microorganisms. Food utensils such as cutting boards, knives, spoons, bowls and other equipment used in food preparation which may become contaminated during food processing and preparation is another major source of microbial spoilage.

Microorganisms when it contaminates food has great effect on the food quality and safety. When they contaminate food, they produce substances that change the colour, texture, consistency, odour and flavor of the food, rendering the food unfit for consumption. When the quality of the food is affected or damaged, the food is unsafe for consumption as it may lead to food borne illnesses.

Microorganisms that can cause food borne illnesses are: Pathogenic microorganisms such as Clostridium botulinum, Clostridium perfringens, Staphylococcus aureus, Bacillus cereus, Listeria monocytogenes, Salmonella spp., Campylobacter spp. Escherichia coli, Shigella spp., Yersinia enterocolitica and many more. These microorganisms when they contaminate food, damage the food quality making the food unsafe for consumption.


Food is one of the basic necessities of human. Therefore, there should not be such problem that can cause serious health issues to protect consumers. As a result, there is need to control microbial spoilage of food by preventing access of microorganisms to food, inhibiting their growth and using thermal and non – thermal methods to inactive them. Good personal hygiene should be practiced, also good manufacturing and handling practices are very important means of reducing the baseline microbial load and increasing shelf life.

The implementation of good handling practices (GHPs) entails the use of appropriate sanitary measures to prevent microbial contamination and assurance of optimum sanitary conditions for processing food products. By implementing an effective good handling practices (GHPs) and good manufacturing practices (GMPs), microbial contamination will be avoided and this will ensure that food is of good quality and safe.


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