This is the fifth session of the food science basics course developed by foodcrumbles.com. This session covers the fundamentals basics of microbiology, with a focus on microbiology in food. Both the concept of pathogens as well as useful micro organisms will be introduced. It is meant for those with a limited background in food science but with an interest in improving their understanding of food. For example: food bloggers, professionals in the food industry, (high school) students and chefs.

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Food Science Basics
Session 5:
Food Microbiology Basics

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Ready, to immerse yourself in
the world of food science?
• Ever wondered why bananas turn brown?
• Never sure which microorganisms in food can be harmful?
• Ever wondered why your chocolate mousse stays light and
fluffy?
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• Ever wondered why your pancake batter rises
and forms air bubbles when baked?
• Never understood why your newly developed
product changes color?

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Week 5
• This deck is part of a 6 week course on the basics of food science,
discussing all of these topics!
• It’s a course for, amongst others:
• Food Professionals
• Food Bloggers
• Chefs
• (High school) students
• Besides food microbiology (this week’s topic) we’ll be discussing: food
chemistry, food physics and some food packaging!
• Want to take the complete course (including quizzes)? Sign up at:
https://foodcrumbles.teachable.com/courses/food-science-basics/
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Let’s get going!
After two sessions packed with food chemistry, an introduction to food
physics it is time for a super relevant topic for making safe food: food
microbiology.
This week we'll be zooming in on the following:
• What are microorganisms?
• The three main types in food
• The bad stuff: pathogenic micro-organisms in food
• The good stuff: useful micro-organisms in food
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What are micro organisms?
• Micro organisms are very small living organisms. A single micro
organism can only be seen with a microscope. Only when very large
numbers of micro organisms are present will you be able to see them
(think of moulds growing on stale bread).
• In food there are three main types of microorganisms:
• Bacteria
• Moulds
• Yeasts
• (And some others, such as viruses, but we’ll focus on the three mentioned
above)
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Bacteria
• Bacteria are very simple micro organisms. The consist of only one simple
cell and have very simple shapes such as rods or little ball shapes. They
multiply by splitting themselves in two.
• There are a lot of different bacteria and they can be grouped in a lot of
different ways. One method is to group them based on their oxygen needs:
• Bacteria that grow without any oxygen are called anaerobic.
• Those that need oxygen are aerobic.
• Some bacteria need a little oxygen, but cannot stand large quantities:
microaerophilic.
• There are also bacteria who don't need oxygen, but can handle it, others don't need
it and cannot handle it either.
• Bacteria can also be grouped by their family names. However, for this
course, I prefer using a split based on their behavior and presence. It makes
it far easier to apply.
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Moulds
• Moulds have far more complex shapes than bacteria. They aren't simple
rods, instead, they'll often have hairy structures, or shapes like a plant.
They can form these structures since they don't exist of just one cell but
are multi-cellular. Of course, they're still small, generally about 5-10 micron
only.
• Moulds need oxygen to grow. There are only a few moulds which can grow
a little when there isn't any oxygen. However, not all moulds might need as
much oxygen in the air as we do.
• Whereas most of the bacteria are very sensitive to their environment, such
as pH or water activity, moulds are a lot less so. A lot of them are able to
withstand pretty harsh situations.
• Moulds (and yeasts from the next section) both belong to the group of
fungi.
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Yeasts
• Yeasts are very similar to moulds, they also belong to the fungi but consist
of just one cell instead of several. This means their structures are a lot less
complex. It is often just a ball or ellipse form.
• Just like moulds yeasts need oxygen to grow. However, more of them are
able to grow under anaerobic (thus without oxygen) conditions as well.
• Yeasts can handle a wide range of pH-values. Some yeasts can tolerate very
high sugar concentrations, this is often a challenging environment due to
the lack of available water (see previous slide deck on food physics).
• One of the most famous yeasts is Saccharomyces cerevisiae, which is used
when making bread.
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The bad stuff: pathogenic
micro organisms
Within these groups of micro organisms there’s an important spilt to
make when it comes to food:
1. Pathogenic micro organisms: these are micro organisms which can
make you sick
2. Non-pathogenic micro organisms: these don’t make you sick and
when used in food some of them even have very beneficial
properties.
We’ll start by discussing the ‘bad stuff’: the pathogens.
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The bad stuff: pathogenic
micro organisms
• The reason food microbiology is such an important topic when it comes to
food safety is due to the bad stuff: the pathogenic micro organisms. If too
high concentrations of such a micro organism are present on your food,
you might get sick.
• How sick you get, what type of sickness and how many micro organisms
are required to make you sick depends on the micro organism.
• There are a lot of different types of pathogenic microorganisms. We will
discuss just a few to give you a feel for the types of things you should take
into account. These are five of the most prevalent food infection causes
and a lot more common than you might think.
Please note, this information is provided for educational purposes only. In no way can I be held responsible for
any actions based upon this content. If you are looking for food safety guidelines/regulations, please refer to a
(local) expert.
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The bad stuff: pathogenic
micro organisms
• This is the main reason you shouldn't eat raw chicken. Salmonella can
often be found in chicken meats and can grow both with and without
oxygen, but not at temperatures above 7°C. Fortunately, Salmonella
cannot withstand heat well, heating them to 70°C for about a minute
will kill most.
• Salmonella can cause two types of diseases (depends on the type of
Salmonella present on your food):
• One occurs within only a few hours or days, causing nausea, fevers, diarrhea,
etc. This will probably only last for a dew days (assuming you were healthy
before).
• Or one that might not show until a week later. This one is more severe and
often has to be treated.
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Salmonella

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The bad stuff: pathogenic
micro organisms
• Listeria grow and live in the ground and can be found on all sorts of
raw products, such as dairy or meats. Listeria monocytogenes is a
quite strong and hardy bacteria, it can still grow in your refrigerator
and it can withstand high salt contents (which a lot of other bacteria
cannot). Only when the pH is as low as 4,5 does it stop growing. Just
like Salmonella, Listeria can be killed by a heat treatment of around
70°C.
• Once Listeria has entered the body it can cause quite an intense
infection, especially for those with a weakened immune system.
Also, Listeria monocytogenes is well known for pregnant women, it
can cause infections of the unborn, even leading to miscarriages.
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Listeria Monocytogenes

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The bad stuff: pathogenic
micro organisms
• E. coli is a family member of Salmonella, both belong to the
Enterobacteriaceae. E. coli is a regular bacteria in our own guts,
where it has several beneficial functions. However, a few specific
types of E. coli can be very harmful and cause disease.
• In animals E. coli is also commonly present. It is part of the natural
habitat. Therefore it is often hard to fully eliminate. The most
important job for manufacturers is to make sure it stays inside the gut
or on an animal’s hide instead of on the final product. The most
important ones regarding disease are: EIEC, ETEC, EHEC and STEC.
• Again, proper heating of your products will kill these bacteria.
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E. Coli – EHEC & STEC

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The bad stuff: pathogenic
micro organisms
• S. aureus is also a bacteria that is very common in and on the human
body. Contamination of food with this bacterium can often occur
simply from the person handling the food.
• This bacterium doesn't grow at temperatures below 6,5°C.
• S. aureus causes disease through the Enterotoxins it produces.
Whereas S. aureus can be killed by heat treatment, this is a lot harder
when it comes to Enterotoxins. These can often resist 100°C for up to
an hour.
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Staphyloccocus Aureus

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The bad stuff: pathogenic
micro organisms
• This anaerobic bacteria produces one of the most toxic toxins we
know of. Even a very small dose of this toxin is sufficient to initiate a
very severe disease which in many cases will be deadly. Even more
tricky is the fact that these bacteria can form so called spores. These
spores can be highly heat resistant and can withstand harsh
situations, such as low pH-values and high salt and sugar
concentrations.
• Therefore, all products with a risk of C. botulinum contamination
should be sterilized (heat treatment at high temperatures for a
prolonged duration) or have a pH value lower than 4,5.
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Clostridium botulinum

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The bad stuff: pathogenic
micro organisms
• There is a lot more to learn about micro-organisms, but I've tried to
stay clear from too many disease discussions and focus on the
influence of the foods on their growth.
• One topic that has to be mentioned though is cross-contamination.
Micro-organisms can easily go from one food product to another,
simply through touch or when you use the same cutting board or
knife for a product.
• Foods that have a high risk of contamination (e.g. chicken) should be
kept away from food you're planning to eat raw (since they don’t gt
the heat treatment to kill the micro organisms).
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Cross contamination

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The good stuff – Useful micro
organisms
• Luckily, it's not only bad stuff when it comes to food microbiology. We
also need micro-organisms in quite a lot of cases when making food.
We will discuss a few of the most important and common examples.
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The good stuff – Useful micro
organisms
• Yeasts are probably the most well known positive micro-organisms.
Loads of us use yeast regularly when baking bread or other baked
goods. Yeast sold in stores is often a dry powder. Just realize, there's
life in these powders!
• During the rising process of bread, the yeast consumes sugar and
transforms this, amongst others, into ethanol and carbon dioxide. The
carbon dioxide is a gas and will cause expansion of the dough. The
ethanol produced will evaporate again during the baking process.
• Without yeast it wouldn't be as easy to make the well known fluffy
breads we commonly eat nowadays.
• Read more on foodcrumbles.com on yeast & fermentation!
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Yeasts & Bread

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The good stuff – Useful micro
organisms
• Lactic acid bacteria are very common in a lot of foods, especially
when foods start getting bad. Souring of milk as well as sour meat are
caused by lactic acid bacteria. They do not necessarily cause disease,
but are a good sign of when a product is starting to go bad.
• They are anaerobic and form lactic acid (hence the name) when
growing and digesting their 'food'. There are a lot of different types of
lactic acid bacteria.
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Lactic acid pickles

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The good stuff – Useful micro
organisms
• Proper pickles are made using lactic acid bacteria. The pickles are
immerged in a liquid with spices, herbs and salt and left in this liquid
for up to several weeks at a comfortable temperature for the bacteria
to grow (18-20°C). Some bacteria might be added at the start of the
process, but otherwise the process will proceed by itself. The pH of
the pickles will sink during this process due to the acids produced by
the bacteria.
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Lactic acid pickles

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The good stuff – Useful micro
organisms
• There are a lot of other products for which micro-organisms play an
important role. We won't discuss all, but let's name a few:
• Cocoa (fermentation of the beans)
• Coffee
• Beer
• Sauerkraut
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Others

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The good stuff – Useful micro
organisms
• This has been a very quick and basic coverage of food microbiology.
It’s a huge topic and we’ve only scratched the surface. Hopefully it
has given you the tools and knowledge to proceed from here.
• Do not forget to take the quiz of this week's course topic (if signed up
for the course)! The quiz will not only test whether you've understood
what we've discussed, but will also include some nice assignments to
help you improve your understanding and knowledge.
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The good stuff – Useful micro
organisms
• When it comes to food disease and prevention there's a well known
book, made by the FDA outlining all the most important food
pathogens. It's appropriately called the 'bag bug book' and can be
downloaded online. It's one of the sources I've used for this course.
• For those speaking German, I would also recommend
'Lebensmittelmikrobiologie', a nice concise book discussing a wide
variety of topics.
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Further reading

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