What is Food Microbiology?

The subdivision of microbiology that deals with the interaction between microbes and food particles are called food microbiology. This scientific study incorporates both beneficial and harmful microbes and their effect on the food production, food storage, and health of human beings.

How do microorganisms contaminate food?

There are multiple sources that the microbes can reach the food. Some of the major ones are as follows:

  • Dust particles and air
  • Soil
  • Impure water
  • Contaminated and unwashed utensils
  • Skin and fur of animals
  • Plants or products derived from plant parts
  • People who handle food products
An Image of a spoon and a fork contaminated with microbes.
CC-BY RF I Image Credits: https://www.mauritius-images.com

Intrinsic and extrinsic components of microbial growth in food

Intrinsic factors can be defined as related or inherent to the food. Several intrinsic factors influence the probability of microbial growth in food substances. Microorganisms lack internal regulatory functions and thus are severely affected by the food's pH level. Optimally, most microbes favor a pH near 7, and their growth is inhibited in acidic pH. Along with the pH, other intrinsic factors such as the food's moisture content, nutritional composition, and the presence or absence of antimicrobial components also determine the growth rate of microbes.

Extrinsic components are the ones that determine the growth of microorganisms and are external to the food. They include factors related to the environment where food is stored. The temperature range, humidity, and the storage environment's gaseous composition are extrinsic factors. Microbes generally require a moderate temperature range for growth. Extreme temperature inhibits microbial growth.

Roles of microorganisms in food microbiology

In general, the microorganisms related to food microbiology are grouped into three categories depending on their roles. Some microbes are important as they help in fermentation and also serve as probiotics. These are beneficial microbes such as Lactobacillus. The other two groups of microorganisms have harmful actions; one causes the transmission of diseases via food. They are foodborne pathogens such as Human Norovirus. The other group is the one that results in the deterioration of food particles or spoilage, such as Streptococcus spp.

Positive roles of microbes

Beneficial microorganisms help improve the health of an individual and play an essential role in the production of various food products. These roles can be better understood with the following examples:

  • Role in food production: Several microorganisms are used for preparing food products through fermentation; thus, that food is called fermented food products. The dairy products derived from bio-processing milk, beverages such as wine, and other edible substances like bread are examples of fermented foods. They also help to improve the quality of the food products.
Name of the MicrobeType of MicrobeFood Product
Acetobacter malorumBacteriumVinegar
Aspergillus oryzaeFungusSoy sauce
Saccharomyces cerevisiaeFungusBread
Saccharomyces cerevisiae and LactobacillusFungus and bacteriaWine
Streptococcus thermophilus and Lactobacillus bulgaricus (lactic acid bacteria)BacteriumYogurt
Saccharomyces cerevisiaeFungusBeer
Streptococcus salivarius ssp. thermophilusBacteriumMozzarella cheese
Penicillium roquefortiFungusBlue cheese
Leuconostoc mesenteroidesBacteriumVegetable pickles
A microscopic image of Penicillium roquefortii; the fungus used in the production of blue cheese.
Penicillium roqueforti
  • Probiotic microorganisms: The microorganisms that reside within the body and function to improve physiological activities or health conditions are called probiotics. Generally, the intestinal region of the digestive tract comprises a unique set of probiotic microbiota in every individual. These microorganisms help improving digestive functions, provide defense against harmful microbes, and enhance the absorption of digested nutrients. Microbes such as Lactobacillus and Saccharomyces boulardii are probiotics commonly found within the body. Fermented food products such as yogurt are a good source of probiotic organisms. Other than these, probiotics are also taken as food supplements. Yakult is an example of a commercial probiotic supplement that is available in the form of fermented milk.

Negative roles of microbes

The negative impact of microorganisms in food storage and production can be grouped under food spoilage and the spread of disease via food.

  • Spoilage of food: Certain microorganisms or enzymatic products of microorganisms lead to the spoilage of food products. The growth of these microbes in food drastically changes the nutritional and chemical composition of the food. Both bacterial and fungal groups have members that lead to food spoilage. The spoilage can be observed by uncontrolled growth of microbes on food, deterioration of food structure, alteration in color, and rotten smell. The bacterium Clostridium botulinum is a bacterial species that causes the spoilage of meat products or poultry products. Fungal molds are common causes for the spoilage of fruits and bread.
A two-part image shows fresh and edible strawberries and strawberries spoiled due to microbial growth
Comparison between fresh and contaminated fruits
  • Spread of diseases: The spread of infectious diseases by consuming contaminated food products is the common cause of illness. Such diseases are termed foodborne diseases, and the pathogens are termed foodborne pathogens. Microbes can inhabit food in multiple ways, and once these contaminated foods are consumed, it causes diseases. Some common examples of microorganisms that cause foodborne diseases are listed below.
MicroorganismDiseases/Disorders caused by them
Clostridium botulinumBotulism, disruption in swallowing, eye movements and breathing issues are related to it.
Salmonella spp.Diarrhea, fever, pain in the stomach and watery stools are related to this disease.
Toxoplasma gondiiToxoplasmosis is characterized by fever and pain in the muscles.
Vibrio vulnificusGastroenteritis's symptoms include nausea, pain in the abdominal region, diarrhea, and fever.
Listeria monocytogenesListeriosis, nausea and pain in muscles are common symptoms.
CampylobacterCampylobacteriosis, diarrhea (mostly bloody), vomiting, fever and nausea are associated with this disease.
Cronobacter sakazakiiEnterocolitis, the digestive tract is inflamed.

Why is food safety important?

The assurance of the safety of food products before consuming them is very important. Food safety includes checking food at different stages, namely, the preparatory, handling, and storage. Quality checking of food to ensure it is fit to be consumed and free from pathogenic microorganisms is crucial for the food industry. Every country has its own set of guidelines and laws to ensure food safety. All these guidelines are under two concepts: HACCP (Hazard analysis and critical control points) and GMP (Good manufacturing practices).

HACCP focuses on preventing potential risks in food products, and GMP is a standard guideline for food production.

Microbiologists have developed several methods to ensure food safety. Food preservation, processing technique, and packaging technique are common methods.

Food preservation

Food preservation refers to all the methods utilized for preventing microbial growth and increasing the shelf-life of food products. It incorporates heating, dehydration, fermenting, freezing, alcoholic immersion, and the addition of oil, salt, sugar, or some preservative agent.

Processing techniques

Processing techniques include how food products are handled. The methods of handling raw ingredients, cleaning food products, and cooking are part of food processing.

Packaging techniques

Packaging techniques discuss how food (both raw and cooked) packed influences the microbiome of the food. The use of vacuum packing, canning, and proper selection of packaging material enhances food safety.

Common Mistakes

Generally, it has been observed that people assume food microbiology to be only associated with the spoilage of food and methods used for preventing spoilage. In reality, the microbiology of food is a broader field associated with food science. It also incorporates microbes important or beneficial in food production and preservation.

Context and Applications

This topic is significant in the professional exams for both undergraduate and graduate courses, such as

  • Bachelor of Science in Biology
  • Bachelor of Science in Microbiology
  • Bachelor of Science in Food Science and Nutrition
  • Master of Science in Microbiology
  • Master of Science in Food Microbiology
  • Master of Science in Food Science and Nutrition
  • Food Industry
  • Food Production and Quality
  • Application of Microbes in Food

Practice Problems

Q1: What intrinsic factors regulate the growth of microorganisms?

(a) Nutritional content of the food.

(b) Food's pH value.

(c) Moisture content of the food.

(d) All of the above

Correct choice: (d)

Q2: Which of the following is not a technique for preserving food?

(a) Cooking

(b) Freezing

(c) Fermenting

(d) Dehydration

Correct choice: (a)

Q3: Which microbial species cause the disorder of botulism?

(a) Salmonella

(b) Clostridium

(c) Vibrio

(d) Listeria

Correct choice: (b)

Q4: ______ is a  commercially prepared probiotic supplement.

(a) Cheese

(b) Curd

(c) Yakult

(d) Rice

Correct choice: (c)

Q5: Which is a fermented food product that is formed by the action of a bacterial organism?

(a) Blue cheese

(b) Soy sauce

(c) Beer

(d) Vinegar

Correct choice: (d)

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